  The following appendix on the dissection and study of the cat is not intended as a general treatise on methods of preservation and dissection, but attempts only to give the application of well-known methods to the dissection and study of the particular animal with which the book deals. General methods which are referred to but not described must be looked up, if unfamiliar, in the manuals of general methods. Aids to Dissection and Study of the Cat.—A copy of Jayne’s “Mammalian Anatomy” should be in the laboratory for reference. Only the volume on the Bones of the Cat has been issued thus far. Wilder and Gage’s “Anatomical Technology” will be found very useful for methods of work. The plates of Strauss-Durckheim’s “Anatomie du Chat” are exceedingly valuable for the bones and muscles, and should be in the laboratory if possible. Outline reproductions of these plates have been published by H. S. Williams (G. P. Putnam’s Sons, New York, 1875). The use of both the original plates and the reproductions is made difficult by the antiquated nomenclature used for the structures figured. Method of Use of the Present Directions.—Except in the case of the Bones, the order of study of the structures is usually not the same as the order in which they are described. This is of course due to practical difficulties in dissection. The present directions give the order of study, or at least the order of dissection; of course after dissection the structures can be reviewed in the logical order given in the descriptions. But in the first study and dissection, the student is to use these directions for the order of work, while using the body of the book for the descriptions. It will be necessary therefore to keep the book opened in two places,—one in the appendix, for the directions; one in the body of the book, for descriptions. In studying the muscles, for example, the student will follow the order of dissection given in the appendix, but as every muscle is dissected he will find, confirm, and study the description of that muscle given in the body of the book. Other organs are studied in a similar manner. Before commencing the study, read that portion of the preface which explains the use of terms of direction (page VII). Note that the page on which any figure is found may be determined by consulting the list of figures given in the Table of Contents. THE BONES.The bones will of course be studied from dried specimens. These may be prepared once for all and kept in the laboratory from year to year. A number of mounted skeletons of the cat should be at hand; these must be prepared by some one who has skill in such work. Preparation of Separate Bones.—For preparing the separate bones the liquid-soap process recommended by Wilder and Gage (“Anatomical Technology,” p. 107) will be found most convenient. This is as follows: The skin and soft parts are removed as far as possible without injury to the bones. Make the following “liquid-soap” mixture:
Heat these together till a homogeneous mixture is formed. Now immerse the bone or bones to be cleaned in a liquid composed of four parts water to one part of the above liquid-soap mixture. Boil forty minutes; pour off the liquid and renew it. Boil about half an hour longer; then remove soft parts with fingers, scalpel, and brush. The bones may be boiled as much longer in the mixture as is necessary to make the soft parts come away easily. If they are boiled too long, however, the epiphyses will separate from the bones. This is especially likely to occur in young skeletons, which must therefore not be boiled so long as the bones of an old cat. Skeletons prepared in the following rough way are useful for many purposes. The entire body of the cat, or a single limb, is placed in the liquid-soap mixture (after partial removal of soft parts), and boiled till the muscles may be removed, but the ligaments, holding the bones together, remain. Clean thoroughly without removing the ligaments, and allow to dry. The bones are thus held together in their natural positions. Skeletons so prepared are not elegant, but are frequently useful. Disarticulation of Skulls.—The bones of the skull may be separated as follows: Clean the skull in the liquid-soap mixture, as above described. Then fill the cranial cavity with dry rice, beans, corn, or some other seeds that swell much on imbibition of water. Cork up the foramen magnum, and place the skull for twelve to twenty-four hours in water. The swelling of the grain will partially Entire skulls, and longitudinal sections, as represented in Fig. 43, p. 60, should be at hand. Study of the Bones.—The bones should be studied in the order in which they are described. No further special directions for their study are necessary. Study of Ligaments.—It will usually not be practicable for each student to make the dissections and preparations necessary for studying the ligaments. Rather should these be examined on demonstration preparations preserved in the laboratory. Such preparations may most easily be made by using fresh material, and dissecting away muscles and other tissues, leaving only the ligaments connecting the bones. The preparations are then preserved in one or two per cent. formalin. It is difficult to prepare the ligaments satisfactorily on preserved material, because they do not stand out clearly from other tissues in such material, so that they are not easily distinguishable. MUSCLES.Preparation and Preservation of Material.—Formalin forms by far the most satisfactory preservative for anatomical material. It is much better in almost every respect than alcohol, and has the additional advantage of being much cheaper. After injecting with formalin, the cat may be preserved either immersed in a weaker solution of the same substance, or may be kept for a long time simply wrapped in a cloth dampened with formalin. The details of preparation differ according to which method is to be used. In either case, the cat should be killed with chloroform, by placing it in a tight jar or box with a cloth or bit of cotton saturated with chloroform. It is not necessary to bleed the specimen. When the cat is dead, remove it to a tray, place it on its back, and tie the limbs loosely so that they will remain outspread. Expose the femoral artery in the thigh, as follows: Make a median longitudinal incision through the skin of the abdomen, from a point an inch or two caudad of the xiphoid process to the pubis. Make an incision passing from near the middle of this obliquely laterad onto the thigh, for about three inches. Reflect the two flaps in the angles between these cuts, then with forceps and tracer isolate the femoral artery just as it passes into the thigh (Fig. 127, a). Make with scissors an oblique incision in one side of the artery, one-half to one inch from the point where it leaves the abdominal cavity. Introduce a canula directed toward the body, and tie it in place. 1. If the cat is to be preserved immersed in a solution of formalin, it should now be injected with a five per cent. solution of commercial formalin in ordinary water (commercial formalin 5 parts; The cat may now be preserved in a one per cent. solution of formalin. Before immersing it in the formalin it is well to remove the hair in some way, otherwise this will hold much water and be very inconvenient in dissection. The neatest method is to cut off the hair with scissors; this takes some time, however. If the skin-muscles (p. 93) are not to be dissected, the skin may be removed. It is well in this case to leave the skin on the sides of the head and on the feet. It is not necessary to open the abdominal cavity, after injecting with the five per cent. formalin. If there is at any time reason to suspect that the viscera are not keeping well, the abdominal and thoracic cavities should be filled with five per cent. formalin by making a small hole through the body wall into the cavity, introducing a canula, and injecting till the cavity is full. The specimen should be kept in a jar or other vessel and should be completely immersed beneath the one per cent. formalin. Any parts projecting above the fluid may be attacked by mould. If a part is found to be moulded, it should be submerged, when the mould will be killed. The mould injures the specimen if allowed to grow for a long time, but if discovered soon, no very serious harm results. During dissection, exposed parts of the body should be kept from drying by covering with a damp cloth. Specimens preserved in formalin dry out much less quickly than those preserved in alcohol. 2. For some purposes it is much more convenient to preserve the material without immersing it in a vessel of formalin. Specimens injected with five per cent. formalin, as above directed, would usually keep perfectly without further treatment, but for two difficulties: (1) the specimen may dry; (2) it may be attacked by mould. The drying may be prevented as follows: Use for injecting a mixture of the five per cent. formalin with one-sixth its volume of glycerine. This will dry only very slowly, and if pains are taken to keep exposed parts covered with cloths dampened with the mixture of formalin and glycerine, there will be no trouble from this source. The skin should not be removed from such specimens except as necessary in the course of dissection. The hair will give little trouble, because dry. The specimens should be kept in a tight box, that the fluid may not evaporate rapidly from the cloths used for wrapping. The attacks of the mould present a difficulty not so easily overcome. As long as the specimens are in daily use for dissection, and exposed parts kept covered with cloths saturated with the glycerine and formalin mixture, little or no trouble is to be anticipated. But if the specimens are left untouched for some days, and particularly if exposed surfaces are not kept covered in the manner above recommended, If mould is found at any time to be attacking the material, the attacked part should be cleaned and well wrapped in cloths saturated in the formalin-glycerine mixture. If such means are unavailing, the specimen should be immersed in a vessel of one per cent. formalin and preserved for the future in this. Recourse should be had at once also to this method of preservation if the specimen shows signs of decomposition by having a strong odor. It seems probable that the attacks of the mould might be prevented by mixing some fungicide with the injecting fluid; experiments should be made in this direction. There are many advantages in preserving the material if possible without immersing it. All parts retain their color and pliability much more completely, so that the different structures are much more easily distinguishable. The method above described, by the use of formalin and glycerine, is to be recommended when the material is to be worked on every day or so and is not to be kept longer than a few weeks. It is usually not very satisfactory in warm weather, however. If some method can be devised of entirely preventing the attacks of the mould, this will be an excellent method of preserving anatomical material. The same specimens used for the study of the muscles will serve also for the spinal cord and brain if prepared by one of the methods above described. (For the viscera, blood-vessels, and nerves, other specimens will have to be prepared; for these, directions are given later.) Muscles to be Dissected.—It will probably usually be impossible in a given course of study to dissect all the muscles of the cat. The instructor will of course select such as seem most advisable to him. The following may perhaps be recommended as a good selection for a fairly extensive course: Muscles of the Fore Limbs (pp. 436-439); Muscles of the Neck and the Deep Muscles of the Head (pp. 439-441); Muscles of the Wall of the Thorax and of the Abdomen (pp. 441-442); Muscles on the Ventral Side of the Neck (p. 442). If the superficial facial muscles (excluding those of the ear) can be studied from a preparation, this will be a valuable addition to a course (pp. 434-435). DISSECTION OF MUSCLES.General.—In dissecting muscles a prime requisite of successful dissection is to keep the muscles clean. Fat, connective tissue, etc., is to be carefully but thoroughly cleared away from the surface of muscles and from between them. Frequently when it seems impossible to distinguish the structures described, all difficulty will vanish as soon as the dissection is thoroughly cleaned. In transecting a muscle, work under it completely from one edge to the other (except in case of very wide muscles), then introduce the scissors or scalpel, and cut it by a smooth clean cut. Always leave the entire origin with one-half of the muscle, the entire insertion with the other half. The student must be prepared to find in some cases considerable variations from the conditions described. The descriptions attempt to give an account of the usual structures, but specimens showing no variations whatever are undoubtedly rare. DIRECTIONS FOR DISSECTING THE MUSCLES OF THE CAT.I. The Skin-muscles (pp. 93-96, and Fig. 62).These will perhaps not usually be dissected. If they are to be dissected, proceed as follows: Make a ventral median longitudinal incision of the skin from the cranial end of the manubrium to a point opposite the crest of the ilium. Connect the cranial end of this incision with the middle of the lambdoidal ridge by a similar incision through the skin. Make another incision from the manubrium to the spinous process of the thirteenth thoracic vertebra. Connect the caudal end of the first incision by an oblique cut with the root of the tail. Make another incision from the convexity of the knee-joint along the fold of skin which connects the hind limb and body, as far as the incision which leads to the root of the tail. Make an incision surrounding the base of the forelimb. Now reflect these flaps one at a time, working in general from the ventral side toward the dorsal middle line. Take great pains not to take up the thin skin-muscle with the skin. In this way all of one side of the body will be uncovered. The cutaneus maximus (Fig. 62, b) and a part of the platysma (Fig. 62, a) will be thus exposed. Read and verify the descriptions of these muscles (pp. 93-96). The cranial portion of the platysma cannot be seen at this stage, but should be dissected in connection with the muscles of the face. II. Superficial Muscles of the Face and Head (pp. 96-107, and Figs. 63 and 64).These will perhaps not usually be dissected by the student. They should be studied on a well-dissected laboratory preparation, if possible. If they are to be dissected, this should be done if possible on a fresh specimen, as it is very difficult to dissect them on preserved material. Proceed as follows: The skin should be removed with care from the sides and top of the face and head, without injury to the external ear. 1. The platysma (p. 95, and Fig. 62, a). Determine its cranial attachments. 2. The intermedius scutulorum (p. 96, and Fig. 63, a). 3. The corrugator supercilii medialis (Fig. 63, b). 4. The orbicularis oculi (Fig. 63, c; Fig. 64, s). 5. The corrugator supercilii lateralis (Fig. 64, k). 6. Notice the frontoauricularis if it exists. 7. The levator auris longus (Fig. 63, g, g'). Transect and reflect. 8. The auricularis superior (Fig. 63, k). Transect. 9. The abductor auris longus (Fig. 63, m). Transect. 10. The abductor auris brevis (Fig. 63, l). Transect. 11. The epicranius (Fig. 63, h, h'). In dissecting this muscle the intermedius scutulorum and corrugator supercilii medialis may be cut by an incision parallel to the middle line but a short distance to one side of it. 12. The zygomaticus (Fig. 64, d). This and the two following muscles may usually be best seen running beneath the fibres of the platysma, without reflecting the latter. If necessary, however, the platysma may be transected and reflected, though this can be done only with great difficulty. 13. The submentalis (Fig. 64, c). 14. The depressor conchÆ (Fig. 64, b). The zygomaticus, submentalis, and depressor conchÆ should now be transected one or two centimeters from the external ear. The corrugatores supercilii lateralis and medialis may be cut across between the eye and the ear, and reflected. There is thus exposed: 15. The frontoscutularis. Transect near the scutiform cartilage. 16. The adductor auris inferior (Fig. 64, o). Transect near its insertion. The external ear is now attached to the head only by the external auditory meatus and the tragicus lateralis muscle. Read the description of the latter (p. 418, and Fig. 67, a), find it beneath the fat which surrounds the proximal portion of the external ear, and cut it as far ventrad as possible. Now cut across the cartilaginous auditory meatus as near to the tympanic bone as possible, and remove the external ear, preserving it for future study. (The remainder of the muscles of the external ear may be studied in connection with the study of the auditory organ.) 17. The orbicularis oris (p. 105 and Fig. 64, i). 18. The zygomaticus minor, if it exists (p. 105, and Fig. 64, e). 19. The quadratus labii superioris (p. 105). a. The levator labii superioris proprius (Fig. 64, f). b. The levator labii superioris alÆque nasi (Fig. 64, g). 20. The caninus (p. 106, and Fig. 64, f'). 21. The buccinator (p. 106). 22. The myrtiformis (p. 106, and Fig. 64, h). 23. The “moustachier” (p. 107). 24. The quadratus labii inferioris (p. 107). III. Muscles of the Fore Limb.A. Muscles connecting the Arm with the Body.—If the skin-muscles have been dissected, as above, cut the cutaneus maximus near its insertion, and reflect it toward the median dorsal line; in this way remove it completely. Remove the platysma in the same way. The first layer of body-muscles is thus exposed. If the skin-muscles are not to be dissected, these may be removed with the skin. If the skin has not yet been removed, proceed as follows: Beginning at the cranial end of the manubrium make two incisions in the skin, one passing to the lambdoidal ridge and the other to the spinous process of the thirteenth thoracic vertebra. Raise the triangular flap thus formed, taking up the skin-muscles with it. 1. The trapezius group of muscles (pp. 115-117, and Fig. 68, d, h, and j) is now exposed and may be dissected. Begin with the spinotrapezius (Fig. 68, j). Read the description of the muscle, then raise its caudal border and work under it until its cranial border is reached and the middle of its inner surface is free. Then transect it, and reflect the two halves of the muscle toward the origin and insertion, clearing the fat, etc., from the inner surface of the muscle and the parts covered by it. Determine origin and insertion. 2. The acromiotrapezius (Fig. 68, h). Dissect in the same manner, being careful not to injure the broad thin tendon which connects the two muscles across the middle line. 3. The clavotrapezius (Fig. 68, d). Separate it carefully, from the cleidomastoid (p. 120). Transect and reflect, as before. 4. The occipitoscapularis (Fig. 73, a, p. 149). Note the strong fascia which separates it from the deeper muscles of the neck. Be careful not to injure adjacent muscles in tracing this toward origin and insertion. Transect. 5. The rhomboideus. Transect. Recognize the levator scapulÆ ventralis (Fig. 68, f), the sternomastoid (Fig. 68, c; Fig. 65, g), and the cleidomastoid (Fig. 65, h). Then dissect— 6. The levator scapulÆ ventralis (Fig. 68, f). Its origin (Fig. 72, c, c') cannot be seen at this stage and should be left until the cervical muscles are dissected. Be careful in transecting this muscle to separate it well from the cleidomastoid. Transect. 7. The cleidomastoid (Fig. 65, h). Its origin cannot be fully seen at this stage. Transect. Make a midventral incision of the skin from the cranial end of the manubrium to a point opposite the crest of the ilium. From the caudal end of this incision make an incision to the root of the tail. From the cranial end of the incision in the ventral middle line make a cut around the base of the fore limb on its caudal side, thus connecting Make another incision from the convexity of the knee at the joint along the fold of the skin which connects the hind limb and body, to the incision which leads to the root of the tail. Reflect the flaps thus formed so as to expose the body and flank, removing the skin-muscle with the skin. 8. The latissimus dorsi (p. 121, and Fig. 68, m). Dissect it up and transect it. Work carefully toward its insertion and note the origin from its outer surface in the axilla of a part of the cutaneus maximus, and at about the same place of a thin muscle, the epitrochlearis (p. 164, and Fig. 65, r), without determining the insertion of the latissimus. 9. Dissect the pectoralis group of muscles (Fig. 65, and p. 144), i.e., the pectoantibrachialis (Fig. 65, m), the pectoralis major (l), pectoralis minor (o), and xiphihumeralis (p). Determine the border of each muscle before lifting it, then work it up at its middle, transect it, and work toward its ends, determining origin and insertion. Refer constantly to the skeleton. 10. Then recognize the teres major (p. 163, and Fig. 75, d; Fig. 77, c) and the common insertion of the teres major and latissimus (Fig. 79, d'); find the bicipital arch (Fig. 65, t') and determine its composition (p. 166). 11 and 12. The serratus anterior and levator scapulÆ (Fig. 73, h and i, and p. 122). In order to expose the origin of these muscles, the external oblique muscle (Fig. 68, p) must be recognized, and that part of it which has its origin from the fourth to the ninth rib should be transected about an inch and a half from its origin and reflected. The thoracic portion of the rectus abdominis (Fig. 73, k) and of the scalenus (Fig. 73, f-f?) should also be recognized and then raised at their outer borders and displaced toward the median line. No part of any of these muscles should be removed or cut except as directed. The serratus anterior and levator scapulÆ should be transected and reflected to get at their origin and insertion. B. Muscles of the Arm(p. 156).—The arm is thus removed from the body and the dissection may be continued on the separated arm. 13. The clavobrachial (Fig. 65, k, and p. 157). Its origin is best seen later. Dissect it up, but do not transect it. Search now with great care for the coracobrachialis. Consult the figures (Fig. 79, c) and descriptions (p. 164), and be especially careful not to injure the long head of the muscle and its tendon. 14. Dissect the coracobrachialis (Fig. 77, f). Cut and reflect it. 15. The subscapularis (Fig. 77, a, and p. 161). Near its glenoid end, its glenoid and coracoid borders are separated by triangular intervals from the adjacent muscles. Transect the muscle by a line connecting the apices of these triangles. Carry an incision from the 16. Dissect the supraspinatus (Fig. 75, a, and p. 159). Cut the strong fascia free from the border of the scapula and its spine. Then transect the muscle and reflect it, being careful not to injure the capsule of the joint. 17. The spinodeltoideus (Fig. 75, e, and p. 156). Find its two borders, beginning with the caudal one. In freeing the very short cranial border do not injure the acromiodeltoideus (Fig. 75, f). Transect and reflect the spinodeltoid. 18. The acromiodeltoideus (p. 157, and Fig. 75, f). Transect and reflect. 19. The infraspinatus (p. 160, and Fig. 75, c). Locate the borders in the region of the great scapular notch. It is difficult to separate the glenoid border from the adjacent teres minor (Fig. 80, c). The separation should be begun at the humerus. Transect the muscle at the great scapular notch and reflect. Be careful not to injure the teres minor (Fig. 80, c). 20. The teres major (p. 163, and Fig. 75, d; Fig. 77, c) should be cut near its junction with the latissimus dorsi (Fig. 77, e). 21. The teres minor (Fig. 80, c, and p. 161) need not be cut. 22. The epitrochlearis (p. 164, and Fig. 65, r). 23. The triceps (p. 166). (a) The long head of the triceps (Fig. 77, i; Fig. 75, g). Find first its medial border and separate it from the medial head. Note the union of its lateral surface with the dorsal border of the lateral head by strong fascia, and then cut the fascia. (b) The lateral head (Fig. 75, h). (c) The medial head (Fig. 79, g, h, and j). 24. The anconeus (p. 170, and Fig. 80, l). 25. The brachioradialis (p. 173, and Fig. 75, k). Reflect it carefully to its origin and insertion. 26. The biceps (Fig. 77, g, and p. 165). The capsule of the shoulder-joint may be opened in order to expose its origin. Its insertion cannot be seen at this stage. 27. The brachialis (Figs. 75 and 79, i, and p. 166). Work under it near its union with the clavobrachial; cut it at that point and reflect it. 28. Extensor carpi radialis longus (p. 173, and Fig. 75, l). Note the oblique tendon on the radial side of the wrist near the insertion of the brachioradialis. A second tendon passes beneath its distal border. This tendon may be separated into a deep and superficial portion. The latter may be traced proximad to its muscle, the extensor carpi radialis longus. 29. Extensor carpi radialis brevis (p. 174). Its tendon is the deeper of the two tendons seen when isolating the tendon of the extensor longus. 30. Extensor communis digitorum (p. 174, and Fig. 75, m). 31. Extensor lateralis digitorum (p. 175, and Fig. 75, n). 32. Extensor carpi ulnaris (p. 176, and Fig. 75, o). 33. Extensor indicis (p. 176, and Fig. 85, c). 34. Pronator teres (p. 179, and Fig. 77, q). 35. Flexor carpi radialis (p. 179, and Fig. 77, r). The tendon of the flexor carpi radialis should not be traced to its insertion until the deep muscles of the palm of the hand have been dissected. 36. Abductor brevis pollicis (p. 184, and Fig. 77, w). 37. Flexor carpi ulnaris (p. 180, and Fig. 77, t). 38. Palmaris longus (p. 179, and Fig. 77, s). In dissecting this muscle be careful not to injure the part of the flexor sublimis (Fig. 77, x) that rises from its surface (see flexor sublimis, p. 181). Cut the palmaris proximad of the origin of the flexor sublimis and reflect it. 39. Flexor sublimis digitorum (p. 181 and Fig. 77, x). Trace one or two of the tendons through the sheaths on the ventral surfaces of the first phalanges. Cut and reflect the radial portion. 40. Flexor profundus digitorum (p. 181, and Fig. 77, u). After recognizing the parts cut through the tendons of the first and fifth parts and reflect them to determine their origin. Then cut through the common tendon so as to reflect the other three parts together. Trace one or two of the tendons to the distal end of the digit. 41. The supinator (p. 177, and Fig. 85, b). 42. The extensor brevis pollicis (p. 178, and Fig. 85, a). 43. Pronator quadratus (p. 183, and Fig. 87, a). The insertion of the brachialis and clavobrachial (Fig. 87, c) and of the biceps (Fig. 87, b) should now be examined. There remain to be dissected the small muscles of the palm of the hand. If these have been injured on the side dissected, the hand of the other side may be used. 44. The lumbricals (p. 184, and Fig. 88, f). 45. The flexor brevis pollicis (p. 184, and Fig. 89, a). 46. The adductor pollicis (p. 185, and Fig. 89, b). 47. The abductor digiti quinti (p. 185, and Fig. 89, i). 48. The flexor brevis digiti quinti (p. 186, and Fig. 89, h). Cut and reflect it. 49. The opponens digiti quinti (p. 186, and Fig. 89, g). Cut and reflect it. 50. The interossei (p. 185, and Fig. 89). IV. Muscles of the Neck and the Deep Muscles of the Head.If the superficial muscles of the head have been dissected according to the directions above given (p. 434), the skin of the head and neck, and the external ear, will have been removed, and the specimen is ready for further study. The parotid and submaxillary glands If the superficial muscles of the head have not been dissected and are not to be, remove the skin from the side of the neck, head, and face to the median dorsal line, removing the thin superficial muscles with the skin. Remove also the parotid, submaxillary, and lymphatic glands (Fig. 65, 1, 2, and 3), and cut through the ear-muscles and the cartilaginous auditory meatus (under direction) and remove the external ear. Clean fat, connective tissue, etc., from the surface of the muscles of the thorax, neck, and head; then dissect as follows: 1. The sternomastoid (p. 139, and Fig. 65, g). Transect and reflect it. 2. The cleidomastoid (p. 120, and Fig. 65, h). This has already been transected; examine now its origin. Remove the large lymphatic gland beneath the sternomastoid and close to the tympanic bulla, and clean the surface of the muscles in this region. 3. The levator scapulÆ ventralis (p. 120, and Fig. 72, c, c', c). This has already been cut; study now its origin. 4. The sternohyoid (p. 140, and Fig. 65, e). In raising it begin at the cranial end and take care not to injure the subjacent sternothyroid (Fig. 65, g'). Transect. 5. The sternothyroid (p. 141, and Fig. 65, g'). Transect. 6. The stylohyoid (p. 112, and Fig. 65, d). Transect. 7. The digastric (p. 107, and Fig. 65, b). Transect, and reflect completely, to the origin and insertion. 8. The mylohyoid (p. 114, and Fig. 65, c). Transect and reflect. 9. The geniohyoid (p. 113, and Fig. 67, g). 10. The jugulohyoid (p. 113, and Fig. 67, b). (The extrinsic muscles of the tongue (p. 228, and Figs. 67 and 96) may be dissected at this point, if desired. (a) The styloglossus; (b) the genioglossus; (c) the hyoglossus. They need not be cut.) 11. The masseter (p. 108, and Fig. 65, a). Cut the superficial and middle layers near their insertions by incisions parallel to the border of the jaw. Cut the deep layer near its origin. Look for the origin of fibres of the temporal muscle from the inner surface of the middle layer. 12. The temporal (p. 110, and Fig. 63, n). Clear its outer surface completely. Cut the temporal fascia transversely and reflect it toward the insertion of the muscle, with the superficial portion of the muscle. Cut through the zygomatic arch at its two ends and remove it, dissecting the fibres of the temporal free from their origin on its inner surface. Then examine the insertion of the temporal. (The muscles of the pharynx (p. 232) may be dissected at this point; for directions, see page 451.) 13. The ceratohyoid (p. 115). To uncover this, the middle constrictor of the pharynx (Fig. 67, j) must be cut and reflected. Cut the mylohyoid, geniohyoid, genioglossus, and the mucosa of the floor of the mouth free from the mandible on both sides, so that the tongue and the floor of the mouth may be drawn ventrad and turned out of the way, exposing the roof of the mouth (as in Fig. 66, p. 112). Cut through one side of the pharynx near the ventral surface and turn the tongue toward the uncut side. The roof of the mouth is thus exposed. Dissect next— 14. The pterygoid muscles (Fig. 66). Remove the mucosa of the roof of the mouth, especially at the sides of the soft palate, and the two pterygoid muscles (p. 111) are exposed. The lower jaw may be removed on one side to get at their origin. (The muscles of the soft palate (p. 230, and Fig. 66, d and e), and the superior constrictor of the pharynx (p. 233, and Fig. 66, f) may be observed at this point, if desired.) V. Muscles of the Wall of the Thorax and of the Abdomen.1. The scalenus (p. 141, and Fig. 73, f-f?). To trace its cervical portion, cut the trachea and oesophagus just craniad of the first rib, cut the pharynx and hyoid free from the ventral side of the head and neck, and remove the pharynx, larynx, oesophagus, and trachea (these should be preserved for future study of the larynx). 2. The transversus costarum (p. 150, and Fig. 73, j). 3. The serratus posterior superior (p. 148, and Fig. 73, l). Transect this at about the middle of the muscle-bundles, and reflect it in both directions. 4. The serratus posterior inferior (p. 148, and Fig. 73, n). Transect and reflect as in the last. 5. The external oblique (p. 153, and Fig. 68, p). Transect it by an incision parallel to its tendon of origin and about an inch from it, and reflect in both directions. 6. The internal oblique (p. 154, and Fig. 73, o). Transect and reflect as above. 7. The transversus (p. 155, and Fig. 69, l). Requires no further dissection. 8. The rectus abdominis (p. 155, and Fig. 73, k). Open its sheath by a longitudinal incision near the linea alba. 9. The external intercostals (p. 150, and Fig. 73, m; Fig. 69, i). To see these, remove the origins of the levator scapulÆ and serratus anterior; also the serratus posterior superior. 10. The internal intercostals (p. 151, and Fig. 69, k). To uncover these, remove the external intercostals from between two or three pairs of ribs. 11. The transversus thoracis (p. 151). To see this muscle, which lies on the inner surface of the thoracic wall, it is necessary to cut through the ribs on one side one or two inches from the sternum, and open the thorax. The muscle can then be observed directly. (The levatores costarum will be dissected later.) VI. Muscles on the Ventral Side of the Vertebral Column in the Neck Region (Fig. 72).Clean the surface of these muscles, removing pharynx, larynx, oesophagus, and trachea, if this has not been done. 1. Longus capitis (p. 142, and Fig. 72, a). 2. Longus colli (p. 144, and Fig. 72, g', g). 3. Levator scapulÆ ventralis (p. 120, and Fig. 72, c', c). Observe its origin. 4. Rectus capitis anterior minor (p. 143, and Fig. 72, b). To see this, cut through on one side the longus capitis and one head of the levator scapulÆ ventralis, and remove the proximal portions, as in Fig. 72. 5. Obliquus capitis superior (p. 136, and Fig. 72, e). 6. Rectus capitis lateralis (p. 143, and Fig. 72, d). VII. Muscles of the Back (p. 123).Remove what remains of the dorsal portion of the latissimus dorsi, serratus posterior superior, and serratus posterior inferior. See that the skin is removed completely to the dorsal middle line, or even for a little distance over onto the other side. There is thus exposed the lumbodorsal fascia (p. 126), covering the muscles of the back. Cut the superficial layer of the lumbodorsal fascia (that from which the latissimus dorsi and obliquus externus abdominis have origin) by an incision parallel to the dorsal median line, and remove it. The muscles of the back are thus exposed (Fig. 69). Observe in the lumbar region the longissimus dorsi (f, f', f); in the thoracic region the longissimus dorsi, the spinalis dorsi (g), and the iliocostal (h); in the cervical region the splenius (Fig. 73, b). 1. The longissimus dorsi (p. 126, and Fig. 69, f, f', f). Notice in the lumbar region the strong deep layer of the lumbodorsal fascia, by which this muscle is covered, and from the under side of which many of the fibres of the muscle take origin. Cut this fascia by an incision parallel to the dorsal median line and about two centimeters from it, from the level of the crest of the ilium as far craniad as the fascia can be cut without cutting into the muscle-fibres (usually to about the level of the last rib). Reflect the medial division of the fascia to the middle line. Reflect the lateral division of the fascia until it passes into the muscle and cannot be farther reflected. Observe then in the lumbar region the medial (Fig. 70, a) and lateral (Fig. 70, b) divisions of the longissimus dorsi, and the portion (b') of the lateral division taking origin from the lumbodorsal fascia (c). Dissect apart some of the muscle-fibres of the longissimus and observe their origin and insertion. Trace the longissimus dorsi into the thoracic and cervical regions 2. The extensor caudÆ lateralis (p. 137, and Fig. 70, f). Uncover this by cutting the lumbodorsal fascia over the sacral region. 3. The iliocostalis (p. 128, and Fig. 69, h). Uncover this completely; note its connection with the longissimus dorsi at the caudal end. Dissect apart some of its muscle-bundles, to see origin and insertion. 4. The splenius (p. 131, and Fig. 73, b). Transect this by an incision beginning at its lateral border about four centimeters from the cranial end of the muscle and extending obliquely craniodorsad to the craniomedial angle of the muscle. Be careful not to injure the longissimus capitis (Fig. 73, g). 5. The longissimus capitis (p. 131, and Fig. 73, g). Transect. 6. The spinalis dorsi (p. 129, and Fig. 69, g). Separate some of its muscle-fibre bundles and trace to origin and insertion. 7. The biventer cervicis (p. 132, and Fig. 69, a). Raise its lateral border, turning it toward the middle line, and transect it near its caudal end. 8. The complexus (p. 133, and Fig. 69, b). Raise its medial border, and transect it near its cranial end. 9. The longus atlantis (p. 134, and Fig. 71, f). 10. The multifidus spinÆ (p. 130, and Fig. 70, d). Remove a part of the longissimus dorsi in the lumbar region, and trace the course of the fibres of the multifidus spinÆ. (If desired the entire longissimus may be removed and the multifidus spinÆ completely uncovered.) 11. The extensor caudÆ medialis (p. 136, and Fig. 70, e). 12. The semispinalis cervicis (p. 133, and Fig. 71, c). Dissect apart some of its fibre-bundles to see origin and insertion. 13. The interspinales and intertransversarii (p. 131) may be seen in the region from which the longissimus dorsi was removed, by removing the bundles of the multifidus spinÆ. 14. The rectus capitis posterior major (p. 134, and Fig. 71, a). Transect. 15. The obliquus superior (p. 136, and Fig. 71, e). 16. The obliquus capitis inferior (p. 136, and Fig. 71, b). 17. The rectus capitis posterior medius (p. 135). Transect. 18. The rectus capitis posterior minor (p. 135). 19. The levatores costarum (p. 150). Remove in a part of the thoracic region a portion of the iliocostal and longissimus dorsi, so as to expose the dorsal ends of the ribs. The levatores costarum will be seen as but slightly separated bundles continuous with the external intercostals. VIII. Muscles of the Hind Limbs (p. 186).Remove the skin and superficial fascia from the lateral surface of the thigh. Examine the fascia lata (p. 186, and Fig. 68, z). Dissect: 1. The biceps femoris (p. 194, and Fig. 68, t). Work under its cranial and caudal borders. Find the tenuissimus (Fig. 90, g) passing obliquely beneath it and reaching its caudal border in its distal half. Transect the biceps without injuring the tenuissimus, and reflect its halves. 2. The tenuissimus (p. 195, and Fig. 90, g). Transect. 3. The caudofemoralis (p. 195, and Fig. 68, s). Transect. 4. The gluteus maximus (p. 187). Transect. 5. The sartorius (p. 197, and Fig. 68, q; Fig. 91, a). Transect. 6. The tensor fasciÆ latÆ (p. 187, and Fig. 68, r). Cut the fascia lata along the distal end of the muscle-fibres and reflect the muscle. 7. The gluteus medius (p. 188, and Fig. 90, b). Work under it carefully, separating it from underlying muscles; cut it close to its tendon of insertion, and reflect it. 8. The pyriformis (p. 188, and Fig. 163, 7, p. 401). Cut and reflect it. 9. The gemellus superior (p. 189, and Fig. 163, 6). This and the next muscle will sometimes be found to be completely united. Transect. 10. The gluteus minimus (p. 189, and Fig. 163, 5). Transect. 11. The obturator internus (p. 192, and Fig. 90, e). Cut it at the dorsal border of the ischium in order to reflect it. The whole origin cannot be seen at this stage. 12. The gemellus inferior (p. 190). 13. The gracilis (p. 198, and Fig. 91, b). Transect. 14. The semitendinosus (p. 196, and Figs. 90 and 91, j; Fig. 92, i). Transect. 15. The semimembranosus (p. 196, and Figs. 90 and 91, i; Fig. 92, h, h'). Transect. 16. The adductor femoris (p. 198, and Figs. 90 and 91, h; Fig. 92, g). Transect. 17. The quadratus femoris (p. 191, and Fig. 90, f). Transect. 18. The obturator externus (p. 191). 19. The adductor longus (p. 199, and Fig. 92, f). This and the following will sometimes be found to be almost completely united. Transect. 20. The pectineus (p. 200, and Fig. 92, e). Transect. 21. The iliopsoas (p. 193, and Fig. 91, c; Fig. 92, d). Only its distal part, near the insertion, can be seen at present. 22. The capsularis (p. 190). Transect. 23. The quadriceps femoris (p. 201). Isolate the rectus femoris (Fig. 92, b) as far as its junction with the vastus lateralis; cut it at 24. The gastrocnemius (p. 203, and Fig. 90, m; Fig. 91, k). It may be raised cautiously near its middle and divided. Care should be taken not to divide the underlying plantaris (Fig. 90, l). After noting the connection of the outer head with the plantaris, the latter may be divided and reflected, together with the outer head. 25. The plantaris (p. 205, and Figs. 90 and 91, l). 26. The flexor brevis digitorum (p. 212). In tracing its tendon note the three branches of the common plantar ligament which emerges from between the second and third tendons. The outer branch is inserted into the fascia covering the base of the fifth digit, while the other two spread out into the bilobed pad of the sole. 27. The soleus (p. 205, and Fig. 90, o). Cut and reflect. 28. The popliteus (p. 206, and Fig. 92, k). Cut very near the origin and reflect. The three following deep muscles on the ventral surface of the shank are covered by the deep crural fascia (p. 206) which separates them from the overlying muscles. It should be removed. 29. The flexor longus hallucis (p. 207, and Fig. 91, m). Divide the muscle at its junction with the tendon. Open the canals on the astragalus and calcaneus and reflect the tendon, cutting the tendon of the flexor longus digitorum near its insertion and dividing at the middle the quadratus plantÆ (p. 213) which may be found inserted into its ventral surface. 30. Flexor longus digitorum (p. 208, and Fig. 91, n). This may be divided very near its origin. 31. Tibialis posterior (p. 208, and Fig. 91, o). This may be divided near its tendon. 32. Peroneus longus (p. 209, and Fig. 90, q). The overlying tendons may be cut in tracing its insertion. 33. Peroneus brevis (p. 210, and Fig. 90, s). 34. Peroneus tertius (p. 210, and Fig. 90, r). 35. Extensor longus digitorum (p. 210, and Fig. 90, p). 36. Tibialis anterior (p. 211, and Fig. 90, n). 37. The extensor brevis digitorum (p. 212, and Fig. 90, u). 38. The quadratus plantÆ (p. 213). It was cut in dissecting the flexor longus hallucis. 39. The lumbricales (p. 213). 40. The interossei (with the muscles of the fifth digit) (p. 214). 41. The tarsal muscles (p. 215). The overlying ligaments must be removed in order to expose the scaphocuneiform. IX. The Diaphragm and the Muscles on the Ventral Side of the Vertebral Column in the Lumbar and Pelvic Regions.Remove the ventral and lateral walls of the thorax completely, as far back as the diaphragm,—leaving only a ring attached to the margin of the diaphragm. Remove the abdominal walls in the same way, as far back as the pubis, leaving the diaphragm in position. Remove the thoracic viscera (the heart and lungs may be preserved for future study). Remove also the abdominal viscera as far back as the beginning of the pelvis, cutting the large intestine where it passes into the pelvis. The dorsal wall of the abdominal cavity should be cleared of fat, blood-vessels, etc., without injury to the crura of the diaphragm. 1. The diaphragm (p. 151, and Fig. 74). Study by transmitted light, to see the tendons, etc. 2. The psoas minor (p. 139, and Fig. 162, 9, p. 398). Find its tendon and separate it from the iliopsoas (Fig. 162, 8) as far craniad as this can be done without tearing the fibres. 3. The iliopsoas (p. 193, and Fig. 162, 8). Find both portions; isolate them as far as it can be done. 4. The quadratus lumborum (p. 139). Free the lateral edge of the iliopsoas from the abdominal wall and turn the whole muscle mediad as far as possible. The bundles of the quadratus lumborum will be found beneath it, against the transverse processes of the lumbar vertebrÆ. With a heavy cartilage-knife separate the two innominate bones along the pelvic symphysis. This is easily done if the knife is inserted exactly into the line of junction of the two bones. Divaricate the edges some distance, so as to make a ventral opening into the pelvic cavity. If necessary, part of the innominate bone of one side may be removed to make the opening larger. Find the thin sheet of fibres forming the levator ani muscle (Fig. 162, 11) at the side of the rectum, attached to the edge of the symphysis. Carefully free the rectum and urogenital organs from this and remove them as far as the anus, leaving the levator ani intact. 5. The iliocaudalis (p. 137, and Fig. 162, 11'). 6. The levator ani (p. 269, and Fig. 162, 11). Remove with great care the levator ani and iliocaudalis of one side, by cutting first the attachment to the symphysis and the ilium, turning the muscle mediad, then cutting the attachment to the tail. There are thus exposed on the lateral wall of the thorax the medial surface of the obturator internus, craniad of it the pyriformis, caudad of it the quadratus femoris. Dorsad of these is the abductor caudÆ internus. 7. The abductor caudÆ internus (p. 137). On the ventral surface of the tail are exposed the following: 8. The flexor caudÆ longus (p. 138, and Fig. 162, 12). 9. The flexor caudÆ brevis (p. 138, and Fig. 162, 13). X. Muscles of the Tail (p. 136).By removing the skin of the tail, all the muscles of the tail are now easily seen. 1, 2, 3, 4, 5—see 5, 6, 7, 8, 9, above (IX). 6. The abductor caudÆ externus (p. 137, and Fig. 113, b; Fig. 70, g). 7. The extensor caudÆ lateralis (p. 137, and Fig. 70, f). 8. The extensor caudÆ medialis (p. 136, and Fig. 70, e). THE VISCERA.Kill the specimen with chloroform and inject with the five per cent. formalin, or the mixture of formalin and glycerine, as for the muscles. (It is an advantage if the preliminary examination of the viscera can be done in a perfectly fresh, uninjected specimen; such a specimen can be kept but a day or two, however. After one day’s examination the skin may be removed and the specimen placed in two per cent. formalin; it will usually be fairly well preserved by this, though the formalin is too strong to make the later dissection pleasant. The specimen cannot be preserved in this manner unless the skin is removed, and a sufficient quantity of formalin used.) Preliminary Examination of the Viscera.(In this preliminary examination the descriptions in the text need not be read, except when this is specially directed.) Wet the hair along a line from the symphysis of the jaw to the pubis. Part it and make a longitudinal incision through the skin along the line. Make a transverse incision of the skin five centimeters caudad of the xiphoid process and reflect the flaps. Incise the body wall from the last rib to the pelvis along the same line as above and also transversely. Reflect the flaps without injuring the ligaments of the bladder. Make an incision through the pectoral muscles between the first rib and the ventral attachment of the diaphragm and about one centimeter from the median line. Make a second incision of the muscles from the cranial end of the first incision along the angles of the ribs to near the dorsolateral attachment of the diaphragm. Cut the ribs and thoracic wall along these incisions with strong scissors; connect the two incisions at their caudal ends, and remove the lateral thoracic wall thus circumscribed. Note the thoracic and abdominal cavities, separated by the diaphragm. Note the following viscera in their fresh condition: A. In the abdominal cavity (without injuring anything) 1. The liver, dark red and lobed, in the cranial part of the cavity, lying against the diaphragm. 2. The gall-bladder partly imbedded in the right median lobe. 3. Displacing the liver craniad, the stomach is seen dorsad of its left lobe. It may extend dorsad of the right lobe, its size depending on the degree of distension. 4. The duodenum or first part of the small intestine leaves the stomach at its right side craniad and makes a U bend, the head of which is directed caudad; it then turns toward the middle line dorsad of the remaining part of the small intestine. 5. The great omentum is a thin fold of peritoneum with many bands of fat. It passes like a curtain from the great curvature of the stomach ventrad of the coils of the small intestine (ileum). It is tucked beneath the mass of coils at the sides and caudally, and folds of it extend between the individual coils. Turn it craniad and note— 6. The numerous coils of the third part of the small intestine or ileum. Turn these to one side and note— 7. The connection of the ileum with the duodenum across the middle line. An indefinite part of the intestine between the ileum and duodenum is called the jejunum, because in man it is found empty after death. 8. The passage of the ileum into the side of the large intestine which begins on the right side just caudad of the loops of the duodenum. The first part of the large intestine is the colon. It may be traced first toward the head (ascending colon), then sinistro-caudad (transverse colon) and then caudad (descending colon). The descending colon returns to the middle line and the large intestine then continues to the anus as the rectum. The blind pouch of the colon which lies caudad of the opening of the ileum is the cÆcum. 9. Turn the duodenum toward the left and note the pancreas, a light red, elongated organ which stretches along the greater curvature of the stomach and thence between the two lines of the duodenal U to its bottom. 10. The spleen, parallel to the gastric portion of the pancreas. It is deep red (darker than the pancreas and not so brown as the liver) and is held against the great curvature of the stomach by a part of the great omentum. 11. The kidneys, close against the dorsal body wall and in contact with the caudal part of the liver. 12. The bladder, in the median line at the caudal end of the cavity, held in place by the suspensory ligament, which passes to the midventral line, and by the lateral ligaments. 13. The mesenteric glands, large grayish-red glands one to four centimeters long, more numerous in the mesocolon. 14. In the female, lying against the ventral surface of the rectum, the uterus. It divides into two horns which diverge. Near the end of each horn the ovary. 15. The peritoneum. Study and understand the description of it (p. 218). Dissect some of it free from the body wall. (Trace the folds by aid of a diagram and model.) B. In the thoracic cavity: 1. The lungs. Each is divided into lobes, three on the left, four on the right. The caudal right lobe pushes the mediastium toward 2. The pleurÆ. Each pleura is a membrane like the peritoneum. It covers the diaphragm and the thoracic walls and is reflected onto the lungs. Hence it is divided into costal and pulmonary portions. Read the description (p. 217) and trace their connection. Each pleura forms a closed sac. 3. The mediastinal septum or median vertical portion formed by the apposition of the medial walls of the two pleural sacs. It divides the thorax into halves. 4. In the mediastinum or space between the halves of the mediastinal septum are seen— a. Ventrally (i.e., in the anterior mediastinum), blood-vessels and fat, and craniad the pink thymus gland. Read the description of the thymus (p. 254, and Fig. 107). b. Dorsally (i.e., in the posterior mediastinum) the trachea (best seen craniad), the oesophagus (best seen caudad), and the aorta. c. In the middle (reckoning in a dorsoventral line) (i.e., in the middle mediastinum) the heart, with the inferior vena cava approaching it from the rear. Prick into the mediastinum and inflate it. Remove the thoracic wall opposite the one already removed, so as to stretch the mediastinum and show it more clearly. Expose the trachea beneath the caudal end of the sternomastoidei. Note the thyroid gland (Fig. 96, 6, p. 229). Insert a blowpipe without injury to the thyroid, and inflate the lungs. Cut the sternum at its caudal end and turn it craniad, cutting the mediastinal septum and noting its double character. Dissect the mediastinal septum from the thymus so as to expose this organ. d. The pericardium, a relatively thick-walled sac, within which the heart lies. The pericardium is covered by the mediastinal septum on each side, but not dorsally and ventrally. Dissect the mediastinal septum from the pericardium. Prick and inflate the pericardium. Open it and expose the heart. Dissection of the Alimentary Canal.Study and verify the descriptions of the organs as they are dissected. I. Salivary glands (p. 223). 1. Keep the mouth open by a cork between the teeth. Find the papillÆ upon which open the sublingual and submaxillary ducts (pp. 223 and 224); remove the mucosa and enlarge the opening and insert a black bristle into either duct. Trace the duct by the bristle as far as possible on the floor of the mouth. 2. Find the white ridge formed on the cheek by the parotid duct (p. 223). It is opposite the molar tooth, and at its cranial end the 3. Remove the skin and the skin-muscles from the side of the face, beginning at the caudal end and working craniad. At the cranial border of the carotid on the ventral side look carefully for the parotid duct with the bristle in it. The duct is then easily traced by the removal of the skin and muscles. Study the parotid gland (Fig. 131, 10, p. 322). 4. Remove the facial vein (Fig. 131, b and c) and lymphatic gland (Fig. 131, 12) covering the submaxillary gland (Fig. 131, 11) and clean its outer surface. Raise it and find the submaxillary duct leaving its inner surface. Reflect the digastric and mylohyoid muscles and trace the duct to the oral mucosa. The remainder of its course is shown by the bristle on the inside of the mouth. 5. The sublingual gland is uncovered in dissecting the submaxillary. Its duct is seen by the side of the submaxillary. It may be pricked near the gland and a bristle passed to its opening. 6. The infraorbital gland. Expose it by removal of the zygomatic arch and masseter muscle. Find its duct by dissecting apart the lobules at its ventral end. Prick the duct and insert a bristle to find its inner opening. 7. The molar gland. Find it by raising the orbicularis oris of the lower lip. By raising its ventral border and dissecting between it and the mucosa the ducts may be found and perhaps pricked and bristles inserted. II. The mouth-cavity. Study the general description (p. 221); the lips and the cheek. Then remove the masseter muscle and the caudal part of the zygoma. Cut through the mandible between the first premolar and the canine tooth. Then disarticulate the mandible, cut the cheek and also the mylohyoid muscle and oral mucosa parallel to the medial border of the mandible, and remove the mandible with the parts thus left attached to it. The organs in the mouth-cavity are thus left exposed and should be studied. To demonstrate the incisive ducts (p. 222) pass a bristle into them. The teeth (p. 224). These should be studied on a skull in which the roots of the teeth have been laid bare by means of the bone-forceps, as in Figs. 93 and 94. The tongue (p. 226, and Fig. 95). Study its dorsal surface, the papillÆ, etc. Then dissect its muscles (p. 228) from the ventral side. The stylohyoid, digastric, and mylohyoid muscles must be removed. Then dissect (a) the styloglossus (Fig. 96, e), (b) the genioglossus (Fig. 96, f), (c) the hyoglossus (Fig. 96, h). Make a transverse section of the tongue to see the intrinsic muscle-fibres. III. The thyroid gland (p. 254, and Fig. 96, 6). Clean the sternomastoid muscles. Cut their interdigitating portions along the median line and reflect them. Find the lateral lobe of the thyroid gland beneath the lateral borders of the sternohyoid muscles. Dissect it, being careful not to destroy the delicate isthmus. IV. The pharynx (p. 231). Remove the large lymphatic gland between the atlantal transverse process and the larynx. Clean the outer surface of the pharynx. Dissect the muscles of the pharynx (p. 232) as follows: (a) The inferior constrictor (Fig. 96, k). (b) The middle constrictor (Fig. 96, j). (c) The glossopharyngeus (Fig. 96, i). (d) The stylopharyngeus (Fig. 96, l). The superior constrictor cannot well be seen at this point; it will be examined later. Disarticulate the cranial cornu of the hyoid from the bulla tympani and make an incision the length of the lateral wall of the pharynx so as to expose its cavity; study. Examine its opening into the mouth-cavity and study the general description (p. 231). Find and study the soft palate (p. 230). Dissect the tensor and levator palatini muscles (p. 230, and Fig. 66, d and e, p. 112), using, if necessary, the specimen on which the other muscles were dissected. Then slit the soft palate lengthwise at one side of the median line to expose the nasopharynx (p. 231). Bring the choanÆ into view by use of a bit of mirror-glass. Pass a bristle into the nares and out at the choanÆ. Pass a bristle through the Eustachian tube into the middle ear. V. Œsophagus (p. 234). After completing the study of the pharynx, leave the larynx and lungs in position and by displacing them toward the right follow the oesophagus to its termination. Open it to see the folds of the mucosa. VI. Cut through the duodenum at its distal end and through the duodenal mesentery so as to separate the stomach and duodenum, with the liver, pancreas, and spleen, from the remainder of the alimentary canal. Float the parts in a dish of water. VII. Study the stomach (p. 234, and Fig. 97). Cut out the ventral wall of the stomach and wash it out, so as to study its cavity, and then continue the cut so as to expose the pyloric valve (p. 235). VIII. Study the duodenum (p. 236). Cut away the ventral walls of the duodenum far enough to expose the ampulla of Vater. IX. Study the liver (p. 239, and Figs. 100 and 101). Expose the hepatic duct of the left lateral lobe near its entrance into the lobe, and follow it so as to expose it fully. If necessary, prick it and inflate with blowpipe in order to follow it. Then expose the cystic duct and other hepatic ducts and follow them to or from the common bile-duct. Trace the latter to the duodenum. If the air does not enter any duct readily, it may be made to do so by manipulating the duct so as to break up the precipitated bile which obstructs it. X. Study the pancreas (p. 241, and Fig. 102). Expose the pancreatic duct near its entrance into the ampulla of Vater, by removing the peritoneum from the pancreas just caudad of the end of the common bile-duct, and by dissecting apart the pancreatic lobules until the duct appears. (If possible, expose also the accessory XI. The ventral wall of the duodenum should now be removed. Cut out a small piece, clean its mucosa with a fine brush and examine the villi with a lens. Demonstrate the coats of the duodenal wall by stripping them off with forceps. XII. The ampulla of Vater (p. 236). Pass bristles through openings in the common bile-duct and pancreatic duct into the duodenum through the ampulla. Slice away the duodenal wall parallel to the bristles until the bristles are exposed. XIII. The spleen (p. 242, and Fig. 102). XIV. Cut the mesentery from the small intestine and colon and slit them both lengthwise, but do not destroy the ileocolic valve. Wash and brush the mucous membrane clean and study the villi, solitary glands, and Peyer’s patches. Study the ileocolic valve (Fig. 99) and open it to study its inner surface. DISSECTION OF THE ORGANS OF RESPIRATION.I. The nasal cavity (p. 243). Review the description of the nasal cavity given under the Bones (p. 59). Study the cartilaginous framework that supports the external nose (p. 243); make a cross-section of the framework near the end of the nose and verify the description (p. 244, and Fig. 103). Without injuring the larynx or tongue saw through the head in a vertical plane and a little to one side of the median line. (If desired, the brain may first be removed from the specimen and preserved for future study. For directions, see page 462. The removal of the brain does not injure the head for the study of the nasal cavity; the skull may be sawn lengthwise in the same way as before.) Wash out the cut surfaces before examining. Find the ventral conchÆ (p. 40), the labyrinths of the ethmoid (p. 43), the inferior meatus of the nose (p. 243), and by bristles the lachrymal duct or canal (p. 245). The lachrymal duct is conveniently found by passing bristles into the openings of the lachrymal canals. One of these is to be found on the border of each eyelid, two or three millimeters from the inner angle of the eye (see p. 410). Cut the oesophagus and trachea at the point where the blowpipe was inserted into the trachea. Separate the tongue, hyoid, larynx, oesophagus, and first part of the trachea from the adjacent parts and remove them. II. The larynx (p. 246). (1) Read the description, studying the cartilages (p. 247) on a preparation (Fig. 104). Then very carefully remove the pharynx and its constrictor muscles, the sternothyroid and remains of sternohyoid muscles, and (2) dissect the muscles of III. The trachea and lungs (p. 251, and Fig. 106). The distal end of the trachea and lungs may now be removed with the heart from the body. The lungs may be inflated with the bellows. The bronchi should then be exposed, cleaned, and followed as far as possible into the lungs. The heart should be preserved for future study. DISSECTION OF THE UROGENITAL ORGANS.A. Excretory Organs.1. Expose the kidney (p. 255, and Fig. 108) by removal of the peritoneum and the surrounding fat, taking care not to open the capsule of the kidney. In removing the fat from the cranial end do not injure the suprarenal body (p. 257), which should be studied. 2. Open the capsule of the kidney and slice away its ventral wall to expose the sinus. After dissecting the contents of the sinus open the pelvis and study the papilla. Pass a bristle from the pelvis into the ureter. 3. Make a median section of the kidney parallel to its ventral surface and study structure (Fig. 109). 4. Trace the ureter to the bladder, being careful not to injure the vas deferens. Study the bladder and its ligaments, structure of its wall, etc. Pass a bristle through the ureter into it and then open it to see the openings of the ureter. Trace the neck of the bladder to the pubis. B. Male Genital Organs.1. Study the external genital organs (p. 257). 2. Carefully remove the integument about the anus and expose the external sphincter ani muscle (p. 268, and Fig. 113, i). Trace it to its origin. Remove the integument of the scrotum and dissect the intercolumnar fascia, the levator scroti muscle (p. 271, and Fig. 113, j), the tunica vaginalis communis, and propria (p. 258). 3. The testis; the epididymis with great care, especially in uncovering the vasa efferentia; the vas deferens and spermatic cord (p. 259, and Figs. 110 and 111). 4. Follow the cord to the external inguinal ring (p. 259) and expose the ring. Dissect off in order from the inguinal canal: (a) The external oblique muscle; (b) the internal oblique muscle; (c) the transversus. In this way the cord is followed with its tunica communis and tunica propria to the internal inguinal ring. 5. Trace the vas deferens (p. 260, and Fig. 111) within the abdominal cavity as far as it can be seen dorsad of the neck of the bladder. 6. The penis (p. 262, and Figs. 111 and 113). Cut the skin along the dorsum of the penis and reflect. Dissect the ligamentum suspensorium penis. Then introduce a bristle into the urethra and remove the integument from the whole penis and identify the corpora cavernosa and corpus spongiosum and the urethra. 7. Remove the fat at the side of the rectum and find the levator ani muscle (p. 269, and Fig. 162, 11). Transect and reflect it. The internal sphincter ani (p. 269, and Fig. 113, h). Find the external opening of the anal gland (p. 239); slit and examine it. 8. Dissect the ischiocavernosus (p. 269) and bulbocavernosus (p. 271) muscles (Fig. 113), and find the bulbus of the corpus cavernosum beneath the former. Cut it free from the ischial ramus. 9. Clean the muscles from the pelvis on the side from which the crus penis is removed, and remove with bone forceps the body of the pubis and the ramus of the ischium. Then trace the neck of the bladder to its junction with the vasa deferentia, and the urethra from that point to the external opening (Fig. 111). Study the compressor urethrÆ muscle (p. 271, and Fig. 113, n). Find Cowper’s glands (p. 261) and the prostate gland (Fig. 113). Dissect the other muscles of the urogenital organs (pp. 268 to 273, and Fig. 113). 10. Slit the urethra on one side throughout its length and find the veru montanum (p. 261); the openings of the vasa deferentia (p. 261), by bristles passed into the urethra from them; the openings of the prostate gland and the openings of Cowper’s glands. 11. Study the structure of the penis (p. 262) by making a cross-section, and that of the glans by making a longitudinal section. Note, if possible, the os penis. C. Female Urogenital Organs(p. 263, and Fig. 112). The kidney and its ducts and the bladder are like those of the male (p. 255), except the neck of the bladder, which will be seen in dissecting the uterus and vagina. a. Without cutting anything examine— 1. The ovaries (p. 264); the ligaments of the ovary (p. 264, and Fig. 112). 2. The uterine tube. Its ostium (p. 264). 3. The body of the uterus (p. 266) as far as exposed. 4. The cornu of the uterus. 5. The broad and round ligaments of the uterus (p. 266). 6. Slit open one Fallopian tube, cornu, and body of the uterus as far as the junction of the divisions of the body of the uterus. b. Remove the ventral wall of the pelvis on one side only and find the vagina and urogenital sinus (p. 267). The levator ani muscle (p. 269, and Fig. 162, 11) must be cut and reflected. 1. Note the constrictor vestibuli, caudovaginalis, and urethralis muscles (p. 272, and Fig. 114). 2. Introduce a probe from the uterus into the vagina and feel with the finger for the hard cervix uteri (p. 266). Then open the vagina on the side, but do not cut the os uteri (p. 266). 3. Examine the cervix uteri and os uteri (p. 266). 4. Introduce a probe through the neck of the bladder and note its emergence into the urogenital sinus. 5. Find the end of the clitoris (p. 267), and its prepuce, and then dissect the integument carefully from about the external opening of the urogenital sinus and note an external sphincter of the sinus (M. levator vulvÆ) (p. 272, and Fig. 114), equivalent to the levator scroti in the male and continuous with the external sphincter ani. 6. Find (if possible) the corpora cavernosa of the clitoris (p. 267) and the ischiocavernosi muscles (p. 269). DISSECTION OF THE CIRCULATORY SYSTEM.I. The Heart (p. 274, and Figs. 115-117).Use the heart from the specimen dissected for the muscles, or from the specimen on which the viscera were studied. 1. Study the outside (p. 275, and Figs. 115 and 116), and learn to recognize all parts. Find the pulmonary veins (p. 275, and Fig. 116, g, h, i) and cut them, thus separating the heart from the lungs. 2. The Pericardium (p. 279). In a specimen the thoracic contents of which have not been injured, dissect the mediastinal septum from the pericardial sac and remove fat about the great blood-vessels so as to expose them all fully. Study their relations. Prick and inflate the pericardium. Slit it lengthwise over the ventricles and reflect it so as to expose its contents. Study the attachment of serous and fibrous layers to the heart and their relation to one another. 3. In dissecting the heart follow the course of the blood, studying each cavity with the aid of the descriptions (pp. 275-279) as you proceed. Dissect as follows: a. Remove the dorsal wall of the right auricle (p. 275) and of its appendage except that part of it to which the venÆ cavÆ are attached. b. Introduce the probe from the right auricle into the right ventricle, and feel with the probe the line along which the ventricular wall joins the septum. Cut along this line so as to turn back the ventricular wall as a flap, which remains attached at the base of the ventricle. c. Introduce a probe through the conus arteriosus into the pulmonary artery and cut along the probe. d. Remove the dorsal wall of the left auricle and its appendage, but do not remove that part to which the pulmonary veins are attached. e. Make a longitudinal incision beginning at the apex and divaricate the lips of the cut as you pass toward the base, thus avoiding injury to the lateral flap of the bicuspid valve. Without injury to the flap or the columnÆ carneÆ, remove the heart-wall at the sides of this incision near the base of the ventricle, as much as necessary to expose the cavity. f. Pass a probe into the aorta. Introduce scissors behind the septal flap of the bicuspid valve and slit the aorta without injury to the bicuspid valve. II. Dissection of the Blood-vessels.Preparation and Injection.—A new specimen must be prepared for the dissection of the blood-vessels. The same specimen may be used, if necessary, for the dissection of the peripheral nervous system,—one side being used for the blood-vessels, the other for the nerves,—but it is much better to use separate specimens for the two systems. Inject the femoral artery of the specimen with either five per cent. formalin, or with the mixture of five per cent. formalin and glycerine, exactly as for the muscles. Then, without removing the canula or waiting, inject the artery with red starch. This is prepared as follows: Mix together equal volumes of vermilion (or red lead), glycerine, and five per cent. formalin. Grind these together in a mortar, so as to destroy the lumps; strain the resulting mixture through fine muslin. This color mixture can be preserved in a closed bottle till it is to be used. Then mix together one volume of dry starch, one and one-fourth volumes of five per cent. formalin, and one-fourth volume of the color mixture. See that no lumps are present. Inject the above red starch mass into the femoral artery. It will drive into the veins the formalin already injected, and the arteries will be filled with the red starch. The veins need not be injected, as they will be found to be filled with the formalin mixture, colored by the blood, so that they can be traced without great difficulty. Dissection of Blood-vessels.—In general the arteries and veins will be traced together. It is an excellent plan to make a sketch of each vessel as it is dissected, showing its origin, branches, and name. This will be a great aid to the memory and will be of much assistance in reviewing the vessels. The sketches can later be combined into a well-ordered drawing. The description of each vessel must of course be studied as the vessel is dissected. In tracing blood-vessels do not grasp them between the forceps-blades, but handle them by taking hold with the forceps of the connective-tissue coats of the vessels. Do not use the scalpel, but pull away the connective tissue and fat with fine forceps, using two pairs of forceps or one forceps and the tracer. Variations are especially common in the blood-vessels, and the student must not be surprised to find considerable deviations from the conditions described and figured in the text. These variations usually present nothing new in principle and are easily understood by comparing them with the structures described. Directions for Dissecting the Blood-vessels.—Make a median longitudinal Find the axillary artery and vein (Fig. 122, f and g) emerging from the thorax just craniad of the first rib, along with the nerves of the brachial plexus. Remove connective tissue, etc., so that the vessels and nerves are well isolated as they pass out of the thorax. Take great pains not to puncture the vessels, particularly the veins. Then remove the left side of the thorax by cutting through the first rib near its sternal end and then near its dorsal end, without injury to the vessels and nerves, cut the other ribs in the same way, and take out the thoracic wall. Now find with tracer and forceps the great blood-vessels leaving the cranial end of the heart (see Fig. 118). Take the greatest pains not to injure them. Find the aorta and aortic arch (p. 281); the left subclavian artery (p. 283) (continuous with the axillary); the innominate artery (p. 282), and the beginnings of its three branches (see Fig. 115). Find also the superior vena cava, the innominate veins, and the subclavian vein, continuous with the axillary vein. I. Study the smaller branches of the thoracic aorta (p. 283, and Fig. 118)—the intercostals, the bronchial and oesophageal arteries, and the first pair of lumbar arteries. (The coronary arteries will be examined later.) II. Dissect the subclavian and its branches (p. 290) as follows: 1. The internal mammary (p. 292). Follow it onto the ventral wall of the abdomen. Follow the vein at the same time (p. 318). 2. The vertebral artery (p. 291). Find its beginning, but do not trace it at present. 3. The costocervical axis (p. 292). Find its beginning, and trace the superior intercostal branch some distance The other branches are not to be followed at present. 4. The thyrocervical axis (p. 293). Find its beginning, but do not trace it at present. 5. The axillary artery (continuation of the subclavian) (p. 294). Follow its branches, tracing at the same time the axillary vein (p. 318). (Consult Fig. 122.) In tracing the blood-vessels, separate the muscles, but do not cut them except where absolutely necessary. (The muscles should be reviewed as the vessels are traced.) The following notes may be of assistance in following the different branches: (a) The anterior thoracic was probably cut in dissecting the pectoral muscles; it may be found, but its distal end is probably cut off. (b) The long thoracic is easily followed. (c) The subscapular. Follow the main artery before dissecting its branches. Where the subscapular disappears between the long head of the triceps, the latissimus dorsi, and the scapula, it may be traced and found again as follows: Remove the skin from the outer side of the shoulder,—taking great pains to remove only the skin and not to injure the vena cephalica (p. 319), a large vein that lies just beneath the skin on the lateral surface of the shoulder, coming from the elbow. The branches of the subscapular will be found appearing on the lateral surface of the arm in the angle between the spinotrapezius, the long head of the triceps, and the infraspinatus. The distal branches may then be followed. (d) The posterior circumflex (p. 296) may be traced distad in a similar manner, by seeking it beneath the caudal border of the spinotrapezius. (Do not injure the vena cephalica.) (e) The other branches of the brachial artery and vein present no difficulty till we come to the collateralis radialis superior (Fig. 122, x). This must be traced with great care, along with the vena mediana cubiti (p. 319, and Fig. 122, y). Remove the skin from the extensor side of the forearm, taking great pains not to remove anything more than the skin. The artery and vein lie beneath the skin and should be traced to the hand (see Fig. 130). Along with the collateral radial artery trace the vena cephalica (p. 319, and Fig. 130, a and c). Follow it across the shoulder, noting the branch to the posterior circumflex vein. The remainder of the blood-vessels of the arm present no special difficulty (see Figs. 123 and 124). Make a diagram of the subclavian artery, as far as dissected. III. Remove the skin from the sides of the neck, exposing the sternomastoid muscles and the external jugular veins crossing them (see Fig. 131). Clean the surface of the sternomastoid muscles, without injuring the vein; separate the two muscles caudad, and cut each close to the attachment to the sternum. Find the sternohyoid and sternothyroid muscles, and cut them close to their attachment to the first rib. Uncover the right side of the thorax in the same way as the left, cut the ribs without injury to the nerves and vessels of the right axilla, cut the internal mammary artery and vein (after tying the latter), and thus remove the sternum with nearly the entire thoracic wall. The blood-vessels of the thorax may now be more completely exposed. (If the nerves are to be dissected on the same specimen, find the phrenic, vagus, and sympathetic nerves (Fig. 157), and take the greatest pains not to injure them.) 1. The coronary arteries and the veins of the heart (pp. 281 and 316). 2. The superior vena cava (p. 316). Find its branches. Trace the azygos as far back as the diaphragm without dissecting it at all. Find the division of the innominate (p. 318) into subclavian and external jugular. Trace next— 3. The external jugular (p. 319). Remove the skin from the side of the face and trace its branches (Fig. 131). The internal jugular, vena facialis profunda, the submentalis, and the deep terminal branches of the posterior facial cannot be followed at this time; veins shown on Fig. 131 should all be found, however. 4. Trace the thyrocervical axis and its branches (p. 293). Add them to your diagram of the subclavian. 5. Follow the common carotid artery (p. 283) and internal jugular vein (p. 320). Find the division of the common carotid into its terminal branches and then dissect its lateral branches and those of the internal jugular (see Fig. 119). 6. The external carotid (p. 285, and Fig. 119). Follow its branches with the exception of the internal maxillary. 7. The internal maxillary (p. 287). Find its inferior alveolar branch first and follow it by cutting away with bone-forceps the ventral border of the lower jaw. To follow its other branches and those of the carotid plexus, remove the zygomatic arch, cut the temporal, masseter, and pterygoid muscles, and cut the mandible behind the incisor teeth and remove it. The branches which pass into the skull are not to be followed at present. The posterior facial vein (p. 323), the vena facialis profunda (p. 323), and the submental vein (p. 323) may be followed at the same time. 8. The internal carotid (p. 285). Follow it to the point where it enters the cranium. 9. Trace the other branches of the costocervical axis (p. 292). To do this, cut the arteries and nerves of the axilla on the side on which they have been dissected, allowing the arm to fall backward. Then trace the branches of the costocervical axis with tracer, scalpel, and bone-forceps, taking care not to injure the vertebral artery. Add these branches to your diagram of the subclavian. 10. The vertebral artery (p. 291). Trace it to the foramen transversarium of the sixth cervical vertebra. Then with bone-forceps follow it to the atlas and into the atlantal foramen. Add this to your diagram of the subclavian. 11. The basilar artery (p. 291) and the other arteries of the brain (p. 289) are best studied on a preparation, similar to that shown in Fig. 121. To obtain such a preparation it is only necessary to remove the brain (for directions, see p. 462) of a specimen in which the arteries have been injected. (12. Veins of the brain and dura mater (p. 324). These can be worked out only with much difficulty, except on specimens injected with gelatine. The skull must be chipped away and the veins followed without destroying them.) 13. Trace the pulmonary veins (p. 315) (filled with red injection) and the pulmonary artery (p. 280). IV. Vessels in the abdominal cavity. 1. Open the abdominal cavity; find the superior mesenteric vein (p. 326, and Fig. 132) in the duodenal mesentery near the border of the pancreas. Inject this in both directions with white starch and then dissect the portal vein and its tributaries without injuring any of the structures in the abdomen (p. 326, and Fig. 132). 2. Follow the inferior vena cava (p. 325) from the heart to the diaphragm and then follow it to its tributaries in the abdominal cavity. 3. Dissect the branches of the abdominal aorta (p. 301) and of the inferior vena cava (Fig. 126). Make diagrams of the vessels dissected and review as far as necessary the viscera concerned. V. The external iliac and its branches (vessels of the hind limbs) (pp. 309 and 329, and Figs. 127, 128, and 163). Follow the branches of the external iliac arteries and the corresponding veins in the same manner as the vessels of the arm were traced, cutting the muscles only so far as absolutely necessary. Make diagrams of the vessels dissected. Make a diagram (a) of the arterial system as a whole; (b) of the venous system as a whole. THE LYMPHATIC SYSTEM (p. 330).It will hardly be found practicable to have each student make a dissection of the lymphatic system, and such parts of it as are to be studied may best be shown on a specimen prepared for demonstration purposes. The thoracic duct and the receptaculum chyli may be demonstrated by the following well-known method: A lean cat is fed with milk about two hours before killing it. An egg may be beaten up with the milk to advantage. Kill the cat with chloroform, and inject the arteries with colored starch through the femoral, in the usual way. The thoracic duct, the receptaculum chyli, and the lymphatics leading to the receptaculum chyli will be colored white by the milk, and can therefore be easily followed. For this purpose the abdomen should be opened, and the left side of the thorax removed, as in the dissection of the blood-vessels. The thoracic duct will be found at the left side of the aorta and may then be traced in both directions. For a more complete study of the lymphatics they should be injected. This is done as follows: Make a glass canula with a small point, and leave the point sharp. Connect this to the syringe by means of a rubber tube. Use a saturated solution of soluble Prussian blue as injecting fluid. Employ a freshly killed animal. For injecting the lymphatics of the limbs, make with some pointed instrument, as the tracer, a small hole in one of the pads on the sole of the foot. Introduce the point of the canula into this opening and The lymphatics of the head may be injected in a similar manner, the canula being introduced into the upper and lower lip, or into the bare surface at the end of the nose. The internal lymphatic vessels may be injected by injecting the lymphatic glands with which they are connected. This may conveniently be done as follows: Draw out to a fine point the tip of an ordinary pipette or medicine-dropper. The point should be fine, but should taper rapidly in a conical fashion, so that when the point is inserted the part of the glass tube behind it will close up the opening. Fill the pipette with soluble Prussian blue; insert the point into the gland, and inject the fluid slowly. The lymphatic vessels passing from the glands will be filled. By injecting thus the large lymphatic gland (“pancreas Aselli”) in the mesentery, the abdominal lymphatics, the receptaculum chyli, and the thoracic duct may be injected. By using thin gelatine colored with Prussian blue as an injecting fluid permanent preparations may be obtained; of course the process of injection is then less simple, and should be looked up in some manual of methods. NERVOUS SYSTEM.I. The Spinal Cord (p. 335).Use the specimen on which the muscles were dissected. (Or if the peripheral nerves are not to be dissected on the specimen used for the blood-vessels, that may be employed.) Make a longitudinal dorsal median incision of the skin, between the back of the head and root of the tail. Reflect the skin for one or two inches on each side of the incision and cut away the muscles covering the neural arches of the vertebrÆ from the third cervical to the seventh or eighth thoracic inclusive. Remove with bone-forceps the neural arch of one of the last cervical vertebrÆ and find the spinal nerve emerging from the intervertebral foramen. Isolate the nerve for a short distance, then proceed craniad, removing the neural arches on one side and isolating the nerves until the third has been uncovered. The ganglion of the second nerve should be sought among the muscles on the dorsal surface between the atlas and axis, and after it has been isolated the The ganglion of the second nerve should be isolated in or near the atlantal foramen, the muscles to which it passes turned aside, and the arch of the atlas removed. Having thus uncovered the first two or more spinal ganglia, proceed caudad, removing the vertebral arches, until the whole cord and its nerves are exposed. Then— 1. Study the cord, enlargements, filum terminale, etc. (p. 334, and Figs. 133 and 136). 2. Slit open and reflect the dura mater (p. 337) for an inch or two. 3. Demonstrate the arachnoid by pulling it off with forceps. 4. Reflect the pia mater in the same way as the dura mater. 5. Study the fissures and grooves of the cord. 6. Cut across the cord with fine scissors at the point where it is freed from its membranes and examine the section. Note the arrangement of gray and white matter and the fissures and grooves, particularly the anterior or ventral. Demonstrate the central canal with the blowpipe. 7. Study the origin of the spinal nerves (p. 337). Count them. Direction of exit? Carefully clean one in the thoracic region from dura mater and connective tissue, with fine scissors, and study dorsal and ventral roots and ganglion (see Fig. 135). Then follow it out and find its dorsal ramus and ventral ramus and the communicating branch of the latter with the sympathetic system. Do not trace the peripheral branches of the nerve at present. II. The Brain (p. 339).The brain will usually be found to be in an entirely satisfactory condition for study in any specimen injected with five per cent. formalin or the glycerine and formalin mixture. The brain is a little swollen, but all parts are well preserved, and the white and gray matter are clearly marked off from each other. Either the specimen used for the muscles or that employed for the blood-vessels may therefore be used,—or if the brain was removed from the specimen employed for the viscera, that will be satisfactory. The following directions for removing the brain are designed for specimens preserved as above. For removing the fresh brain the process is essentially similar, but as the brain is then very soft, care should be taken not to tear it. The fresh brain should be preserved in the alcohol-formalin mixture given below, and should be allowed to rest only on some soft substance, as absorbent cotton. Remove the head from the body by cutting through the neck a little craniad of the first rib if this has not already been done. Remove all skin, muscles, and other soft parts from the head and cervical vertebrÆ, as far as possible. Remove the structures in the orbit by cutting through the zygomatic arch at each end, and removing it. The lower jaw should also be removed, if this has not Have at hand dissecting-instruments and a dish containing alcohol and formalin in the following proportions (Parker and Floyd’s mixture):
In the bottom of the dish should be placed a little absorbent cotton, to support the brain. In removing the brain have at hand entire and dissected skulls and note the relations of parts on these as far as necessary before cutting the specimen. With bone-forceps make a small opening in the parietal bone so as to expose the dura mater, but do not cut through the dura mater. With some blunt instrument free the dura mater from the bone about the opening, and continue to cut away the bone until the dorsal and lateral faces of the cerebrum are fully exposed craniad of the tentorium. The olfactory bulbs (Fig. 137, I) should be exposed carefully and as fully as possible. Cut away the dorsal arch of the atlas and carefully insert the forceps in the foramen magnum and, working as before, remove the squamous portion of the occipital and the parietal bones as far as the tentorium and as far ventrad as possible. Leave the dura mater intact if possible. Free the surface of the tentorium from the dura mater, carefully separate slightly the cerebellum and cerebrum; insert the bone-forceps (not too far) with the blades inclined from without ventromediad, and cut the tentorium on each side. Remove it slowly, cutting adhesions to the dura mater. That part of the dura mater which dips between the cerebral hemispheres is the falx cerebri. Cut the dura mater along both sides of the falx cerebri and remove it by turning it down at the sides and cutting it at the level of the cut edge of the bone. Remove it also from the cerebellum and notice how it dips down on both sides of the tentorium and in close contact with it. Cut the falx at the cranial end between the olfactory bulbs and cut the tentorial dura (cut its adhesions, but do not remove with it the pineal body). The falx and tentorial dura may then be removed. Allow the head to hang sideways over the dish of alcohol-formalin in such a way that the brain will tend to fall out of the cranium. Free the olfactory bulbs from the bone. Then begin at the caudal end and tilt the brain out with the handle of a scalpel. In doing this note carefully and cut the cranial nerves. They should be left with central ends as long as possible, and those on the side which is uppermost should be cut first. In doing this refer to the foramina in the base of the skull and to Fig. 138. Take especial pains also not to break off the hypophysis, which is lodged in the sella turcica. The brain falls out and rests with its dorsal surface on the cotton. Now remove the remainder of the dura mater, carefully cutting all adhesions to nerves. Remove also the pia mater, as far as that can be done without pulling off at the same time parts of the brain-substance. Preserve the brain in the alcohol-formalin mixture. Study of the Brain.—In the study of the brain demonstration specimens are to be used as much as or more than your own specimen. See everything on a demonstration preparation before attempting to expose it in your own specimen. I. Examine the brain of a shark or of a frog. Cranial nerves may be neglected, but the divisions of the brain should be recognized in dorsal and ventral views and in longitudinal sections, and sketched. II. Read the general description of the cat’s brain (pp. 339-343), using your own specimen and a longitudinal section. Cut nothing on your own specimen except when especially directed to do so. Study the cavities on a preparation. Compare the diagrams (Figs. 139 and 140) and the figures of the brain. III. Study the individual parts as follows. To avoid errors make constant reference to preparations and figures. 1. The medulla (p. 344 and Figs. 138 and 141). Use your own specimen and a preparation and dissect out carefully the cranial nerves on your own specimen. 2. The cerebellum (p. 347). Study it entire, then to expose the fourth ventricle (p. 349) slice away with a very sharp scalpel one-half of the cerebellum by making a median longitudinal incision and then horizontal incisions. 3. The pons (p. 347). 4. The mesencephalon (p. 351, and Figs. 141 and 142). Study it first in a preparation. Then study the floor on your own specimen; origin of third nerves. 5. The diencephalon (Figs. 141 and 142). Study the roof and thalami and the pineal body on a preparation and on a longitudinal section; the floor on your specimen. 6. The telencephalon (p. 357). (Note that only one side of this is to be dissected.) a. Study it externally; sulci and gyri (Figs. 145 and 146). b. Examine a preparation showing the corpus callosum (Fig. 147). Then slice away with a very sharp scalpel the top of one hemisphere nearly to the corpus callosum (see the preparation). Expose the corpus callosum on this side to its cranial and caudal borders, by tearing away the brain-substance at its side and above it. c. Raise the corpus callosum at the side and remove it, thus exposing the lateral ventricle in which note the septum pellucidum and fornix, the corpus striatum, and choroid plexus of the lateral ventricle (Fig. 148). (These are to be exposed on one side only, the other being left intact.) d. Expose the anterior and inferior horns of the ventricle and find the hippocampus, the fimbria, caudal part of the fornix, the e. Remove the occipital and parietal portions of the cerebrum, on the side already dissected, so as to expose the roof of the third ventricle and the midbrain in your specimen, and note the pineal body, choroid plexus of third ventricle, and structures on the roof of the midbrain (Fig. 141). f. Remove the choroid plexus or roof of the third ventricle and study again the thalami (Fig. 141). g. Make a longitudinal section of the brain, in the following manner: Use a very sharp large scalpel, or a razor. Have this wet with the alcohol mixture at the time of using. Place the brain ventral surface down on a sheet of cork or a block of soft wood, the long axis of the brain coinciding with the direction of grain of the wood. Holding the brain firmly with one hand, place the wet knife between the hemispheres with its edge resting on the corpus callosum. See that it is in the median plane and parallel with the long axis of the brain. See also that it is not inclined to one side or the other, so that it will make on cutting a median section throughout. The point of the knife should just reach the cork or wood between the olfactory bulbs. Now draw the knife caudad, keeping its point against the cork: the brain will thus be divided. If the section is not exactly median, observe the amount of divergence by placing the two halves together and finding the median ventral line. Then on the half that has too much slice away thin shavings until the cavities are exposed, showing the section to be median. Compare with a demonstration section or Fig. 143. Draw the section and compare with a section of shark’s brain (see Fig. 143). h. Study a series of transverse sections, identifying parts. Observe especially in these sections the fornix, corpus callosum, and ventricles, and the distribution of white and gray matter (see Figs. 149-153). III. PERIPHERAL NERVOUS SYSTEM.(There are some advantages in dissecting the eye with its muscles before dissecting the nerves, as a knowledge of the eye-muscles is presupposed for dissecting some of the cranial nerves. For directions on the eye, see p. 469.) A new specimen should be used, if possible, for the peripheral nervous system, though that used for the blood-vessels can be employed, at considerable disadvantage. Prepare as for the blood-vessels. The arteries should be injected with red starch, to aid in tracing the nerves. 1. The Cranial Nerves (p. 369) and Sympathetic System (p. 404).1. Reflect the skin covering the sternomastoid muscle, and make a longitudinal incision of the muscle so as to expose the carotid artery. Lying along the artery find the combined trunk of the 2. Follow the vagus (p. 378) caudad to its termination. To do this it is necessary to remove one side of the thorax, as in dissecting the blood-vessels. Do not injure the nerves of the axilla, nor the phrenic or sympathetic nerves. For the vagus in the thorax, compare Fig. 157. Find the branches of the nerve; in dissecting them, pull on them to make them tense. They are then more easily visible. To dissect the abdominal portion of the vagus, open the abdominal cavity, and compare Fig. 164 (p. 407). 3. Dissect the sympathetic (p. 404), following it and its branches to the pelvic region (Figs. 156, 157, and 164). 4. The hypoglossal (p. 383, and Fig. 156, b). 5. The glossopharyngeal (p. 378, and Fig. 156, a). 6. The accessory nerve (p. 382, and Fig. 156, c; Fig. 158, 1). Cut away a portion of the tympanic bulla and the base of the skull, sufficient to follow these nerves in the jugular foramen, to the brain. 7. Locate the stylomastoid foramen and pick away overlying tissue until the facial nerve is found emerging and then follow its branches to their distribution (p. 375, and Fig. 155). 8. Expose the ventral surface of the pterygoid muscles just mediad of the angle of the jaw. Divide and reflect them, and the mandibular division of the fifth nerve (p. 373, and Fig. 154) will be found dorsad of them and of the internal maxillary artery. The chorda tympani (p. 375) passes ventrad of the artery to join the lingual. Follow out (1) the lingual branch (p. 375) (with the chorda tympani), and (2) the inferior alveolar (p. 375) by cutting away the ventral border of the mandible. Then cut the mandible near the canine tooth, and pull it to one side, and follow out the muscular branches of the mandibular nerve. 9. Remove the mandible and find the maxillary nerve (p. 371) emerging from the foramen rotundum. Follow its branches and find the sphenopalatine ganglion (p. 372). 10. Remove the zygoma so as to expose the whole ventral aspect of the orbit. Carefully pick away the fat in the orbit without injuring any nerves, so as to expose the four recti muscles and the inferior oblique (see p. 411, and Fig. 166). Find the abducens nerve (p. 375, and Fig. 154), entering the dorsal edge of the lateral rectus, and follow it back. Look on the inner surface of the inferior rectus for the branch of the third nerve (p. 369) which supplies it. Find 11. Trace the third nerve (p. 369) to its foramen of exit and find its branches. Where it passes between the superior and lateral recti, find the ophthalmic nerve (p. 370) by its side and trace its branches. 12. Find the fourth nerve (p. 370), passing outside of the lateral rectus at its origin and entering the superior oblique. 13. Follow the third, fourth, fifth, and sixth nerves into the skull by chipping away the bone and removing the dura. Note the semilunar or Gasserian ganglion (p. 370, and Fig. 138, k) and the origin of the fifth nerves from it, and the relation of the ventral root of the fifth nerve to the mandibular nerve. 2. Spinal Nerves.The spinal nerves may be dissected on the same side used for dissecting the cranial nerves. (If an undissected specimen is used, remove the skin from the side of the neck, and cut the sternomastoid, sternohyoid, and sternothyroid muscles, as directed for the vagus and sympathetic.) Cervical Nerves (p. 383).—The ventral rami of the cervical nerves are to be sought as they pass out between the bundles of the scalenus, or between the scalenus and longus capitis, in the neck. This region has already been uncovered in dissecting the vagus and sympathetic (Fig. 156). Dissect first the second cervical (p. 385). Find its ventral ramus as it emerges between the levator scapulÆ ventralis and cleidomastoid (Fig. 158, 2), and follow its branches,—the auricularis magnus (5) and cutaneus colli (6). Find its dorsal ramus, the great occipital nerve (p. 384), by reflecting the clavotrapezius muscle; the nerve will be found emerging from the underlying muscles close to the craniomedial angle of the clavotrapezius, near its origin. Trace the nerve in both directions. The ventral ramus of the first cervical (p. 385) will be found emerging from beneath the wing of the atlas, a little distance craniad of the second (Fig. 156, j). Trace it. To find its short dorsal ramus, the suboccipital nerve (p. 384), it is necessary to dissect apart the muscles on the dorsal side of the atlas till the nerve is found passing from the atlantal foramen. Dissect the third, fourth, and fifth nerves (p. 385, and Fig. 158). Brachial Plexus (p. 386, and Figs. 159 and 160).—The brachial plexus has been partly uncovered in dissecting the vagus and sympathetic. (If a new specimen or the opposite side is used, reflect the skin from the ventral surface of the thorax and arm, and cut the pectoral muscles, thus uncovering the vessels and nerves of the axilla.) Reflect the skin from the ventral surface of the upper arm. (Do not use scalpel, but tear the skin from the muscles. In this Tie the axillary vein or its two branches in two places, and cut the vein between the tied regions. Leave the arteries as guides for dissection, but remove the veins. Now clean thoroughly the nerves forming the brachial plexus as they pass from the thorax or neck. Be careful not to injure any of the fine nerves or the interconnections of the nerves in doing this. Find and distinguish clearly the fifth, sixth, seventh, and eighth cervical nerves and the first thoracic, as they emerge from the neck or thorax. (Compare Fig. 159 and Fig. 157, V-VIII and I'.) Follow out the branches of the plexus, noting the origin and distribution of each branch, in order to determine its name. To follow the phrenic (p. 388, and Fig. 157, f), remove a portion of the thoracic wall. In following the other branches of the plexus, pull back the skin wherever an exposure is to be made, and separate the muscles. The epitrochlearis may be cut near the elbow, and the clavobrachial near the shoulder. In following the interosseous branches of the median nerve the fifth head of the flexor profundus, and the extensor brevis pollicis, may be cut. As a rule it will not be necessary to cut other muscles. Thoracic and Lumbar Nerves.—One or two of the thoracic nerves (p. 393) should be dissected from the outside by finding the intercostal nerve along the caudal border of one of the ribs and tracing it in both directions. The nerve may be exposed by removing the external muscles covering the rib, and cutting the external intercostal muscles. The dorsal ramus should be traced after the ventral ramus has been studied. The first lumbar nerve (p. 395) should be dissected in the same way. The other lumbar and sacral nerves (pp. 395-400) are best dissected from within. The alimentary canal and its appendages should be removed from the abdomen, leaving only five or six centimeters of the caudal end of the rectum. The kidneys and urogenital organs may be left, to be removed during dissection. (Compare Fig. 162.) Turn one of the kidneys to the other side, and find the second lumbar nerve (Fig. 162, a) appearing at the lateral border of the iliopsoas muscle. Trace it to its origin; trace it also distad, following both branches. It will be necessary to trace the nerves through the abdominal wall, then find them from the outside, and follow them to their distribution. The third nerve (Fig. 163, b) may be found by dissecting apart the fibre-bundles of the iliopsoas and psoas minor, and following in the same way. The kidneys, ureters, vena cava, and aorta may be removed as occasion arises. The remainder of the lumbar nerves may be found in order, in a similar manner. Follow the saphenous nerve and its branches ( SENSE-ORGANS.I. The Eye (p. 410).Use any specimen on which one side of the head has been left intact. Remove the head from the body by cutting through the neck a little craniad of the first rib. Study the eye externally. Observe the eyelids, the conjunctiva, nictitating membrane with its cartilage, and the Harderian gland (Fig. 165); the two openings of the lachrymal duct, the Meibomian glands if possible. Remove the zygomatic arch and expose the orbit and the structures which it contains. Study the periorbita (p. 409), and find the lachrymal gland (p. 410). Study the muscles of the eyeball (p. 411, and Fig. 166). The lateral rectus on the lateral surface will perhaps be first found, and its tendon traced beneath the inferior oblique. Use great care not to injure the levator palpebrÆ superioris. After studying the muscles, find the optic nerve. Cut it and the muscles, and remove the eyeball for farther study. The Eyeball (p. 412, and Fig. 167).—For an examination of the eye it is well to have a fresh specimen and one hardened in formalin or alcohol. The hardened specimen is more essential, however. An eye from one of the specimens used in dissection is usually satisfactory. All accessory portions should be trimmed from the eyeball, leaving only the spherical ball with a short stalk formed by the optic nerve. Observe such features of the eye as can be seen externally: the optic nerves, sclerotic, cornea, iris, and pupil. This should be done Dissection.—Examine the internal structures on a preparation. Then with fine scissors and forceps remove from the eye about one-fourth of the wall, in the form of a quadrant having one point at the optic nerve, the other at the centre of the cornea. The coats of the eye can then be studied on the piece removed, while the other structures will be visible within the eyeball. No special directions are necessary for observation of the structures described, unless it be the capsule of the lens and the zonula ciliaris. The capsule of the lens may be demonstrated by tearing a bit of it off with fine forceps. The zonula ciliaris is easily seen by divaricating the edges of the cut made in removing the quadrant, so as to stretch the fine fibres of which the zonula is formed. II. The Ear (p. 415).(The muscles of the external ear are of little practical importance, and will doubtless usually be omitted.) (1) The External Ear. Read the description of the external ear (p. 415), verifying it by examination and comparison of an ear still covered with integument, in the natural condition, and of a preparation of the isolated cartilages of the ear (Fig. 168). The latter may be obtained by dissecting the skin and muscles from a fresh ear. (2) The scutiform cartilage (p. 418) should be observed in the natural position, and as isolated. (3) The muscles of the external ear (p. 418, and Fig. 169). Those connecting the external ear with other parts of the head have been studied in connection with the facial muscles. The remainder will be studied on an external ear removed according to the directions given on page 435. Remove the integument from the convex surface of the auricle, sufficiently to expose the entire extent of the muscles. 1. The rotator auris. Transect. 2. The adductor auris superior (Fig. 169, 1). 3. The adductor auris medius (2). 4. The transversus auriculÆ (Fig. 63, i, p. 97). 5. The auricularis externus (Fig. 169, 10). 6. The helicis (Fig. 169, 3). To expose this it will be necessary to remove the integument from along the cranial border of the inner surface of the auricle. 7. The antitragicus (Fig. 169, 6). Remove the integument farther if necessary. 8. The tragicus medialis (Fig. 169, 5, 5'). 9. The conchÆus externus (Fig. 169, 9). (4) Remove the tympanic bulla and petrous bone from the rest of the skull, by the use of bone-forceps and scalpel. Trim away all (5) Find the Eustachian tube and study it (p. 423). (6) Study specimens of the bones of the middle ear (p. 423, and Figs. 171 and 172). (7) The middle ear should be studied on a demonstration preparation, then dissected as follows: Remove with bone-forceps the medial side of the tympanic bulla (the entotympanic). Note the two cavities within the bulla, with the shelf separating them. Observe the fenestra cochleÆ. Now remove with the forceps the shelf, first breaking through the middle part, then removing the rest with care. Remove part also of the membranous lining of the cavity, till the inner surface of the tympanic membrane, with the malleus crossing it, is visible. Observe the tensor tympani muscle (p. 424) attached to the malleus by its small tendon. Next, with bone-forceps, fracture the thick, bony portion uniting the caudal end of the petrous with the caudal part of the ring of bone surrounding the external auditory meatus. These two parts may then be separated with the fingers, leaving the petrous bone on one side, the meatus, tympanum, and malleus on the other (Fig. 170). The head of the malleus may then be observed, with the incus attached to it. Note also the stapes, in the fenestra vestibuli, with the stapedius muscle (p. 424) attached to it. (8) The internal ear (p. 424). Note the fenestra vestibuli and fenestra cochleÆ and the promontory (p. 34). Study the cochlea and vestibule on a demonstration preparation and compare with Fig. 173. Then remove the wall of the promontory and find the cochlea. Open the vestibule and find as many of the openings of the semicircular canals as possible. Study the semicircular canals on demonstration preparations, consulting Fig. 173. The semicircular canals may, if desired, be exposed on your own specimen, by cutting away the surface of the bone in places indicated in the description (p. 426), and inserting fine bristles (those from the sensory hairs on the face of the cat are excellent for this purpose). The membranous labyrinth (Fig. 173) may be isolated by decalcifying the petrous bone with ten per cent. nitric acid, then dissecting out the labyrinth. This is an operation of considerable delicacy, but at least one or two specimens for demonstration should, if possible, be prepared thus and kept in the laboratory. [472] |
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