Study of large interior organs in any of the four great bodily cavities especially those in the abdomen.

Digestive Organs of the Horse.—The digestive organs comprise the alimentary canal and the accessories by which the alimentary matter is received and subjected to specific actions, which adapt it for purposes of nutrition. Digestion, therefore, embraces the collective operations and changes which the food undergoes in the alimentary canal.

The whole digestive track from the mouth to the anus which is situated just below the tail, is sometimes called the alimentary canal.

The mouth is an oval cavity at the commencement of the alimentary or digestive canal. In front of the mouth are the lips, one above and one below; at the sides are the cheeks. The mouth is lined with what is known as the mucous membrane, in which are several small openings, from the glands, which are situated about the mouth. Through these the saliva is poured. On the upper part of the mouth the mucous membrane is thrown into ridges, or folds, from 18 to 20 in number. This is a point of importance in connection with bleeding a horse with lampas. It is never safe to bleed back of the third bar because there is a large artery which runs down through the roof of the mouth and enters the hole in the bone just before it reaches this bar. The tongue, which has the chief nerves of the sense of taste, is situated in the mouth; this organ also has a very important part to perform in masticating the food and mixing it with saliva. The teeth, which also take a very active part in the masticating of food, are dealt with under the heading of “Teeth.”

Salivary Glands.—These glands secrete the saliva that is poured into the mouth while the animal is eating. There are only three pairs of much importance. One large pair, one on each side of the throat below the ears, known as the parotid glands, fill up the space between the jaw bone and the neck. This pair has tubes passing around and under the lower jaw and up into the cheek muscles entering the mouth opposite the fourth molar tooth. These tubes, known as steno’s ducts are about an eighth of an inch in diameter and convey the saliva from the glands into the mouth. The next pair are situated under the pair just mentioned. Their tubes enter into the bottom part of the mouth. The third pair are situated under the tongue, one on each side. They pour their secretion into the mouth by several small openings near the front under the tongue. This can be seen by examining the under surface of the tongue closely. This is very important fluid in connection with the digesting of the food.

The gullet is a cavity situated just back of the mouth. It is chiefly made up of muscles which perform the act of swallowing the food. It is lined with the continuation of the mucous membrane of the mouth.

The oesophagus, or the continuation of the gullet, is a tube extending from the gullet to the stomach, and is used to convey the food to that organ. It is made up of two coats, the muscular and the mucous. The former contains fibers which, when once the food enters the tube, contract behind it, forcing it down to the stomach. Its lining is a continuation of the mucous membrane of the mouth and the gullet. In tracing the oesophagus or tube down the neck from the gullet, note that it passes down the left side of the neck, entering the thoracic, or chest cavity, between the lungs over the heart through the large muscular curtain known as the diaphragm, then enters the stomach an inch or two after passing the diaphragm.

The Stomach.—This organ is very small in the horse in comparison with that of the ox. It holds only about four gallons, and is situated just back of the curtain which separates it from the lungs. It lies mostly to the left side. The walls of the stomach being composed of three coats. That on the outside is called the serous membrane, a name applied to membranes which line closed cavities, such as the abdominal cavity. The inside lining is a continuation of the mucous membrane lining the organs before mentioned. The lining in the left part of the stomach or the part where the food is prepared for digestion is the same color as that of the mouth. The lining of the right part of the stomach, which is the true digestive part, is of a deep red color resembling velvet, and when placed under a microscope has the appearance of a honey-comb. When the stomach is empty this membrane is thrown into loose folds. Several small openings may be noticed through which the gastric juice and pepsin from the glands, situated in the walls of the stomach, enters. These are very important fluids as they assist greatly in digesting the food. The third coat is known as the muscular coat already mentioned. Its action is to give the stomach a churning motion, rolling the food around and mixing it with the juices. The opening to the stomach is guarded by a valve which prevents the food from passing back through the gullet. There is also a valve at the opening of the bowels, preventing any coarse, undigested food from entering them. The stomach is held in its place by five large ligaments, and is well supplied by blood-vessels and nerves. Digestion of the food takes place very quickly in the horse in comparison to other animals. Frequently a change of food or working too soon after eating will interfere with the digestion, thus setting up what is known as indigestion. This is a very painful disease in the horse. After the food is acted upon by the juices in the stomach it changes into what is known as chyme, which passes into the bowels.

The Bowels.—They are divided into two parts—the large and small.

The small bowels are 72 feet in length, about one inch in diameter, and are made up of three coats, same as the stomach. The serous coat on the outside contains small glands which secrete an oily material to lubricate the outside of the bowels, which comes in contact with the inner wall of the abdominal cavity. The muscular coat, made up of muscular fibers, is situated between the other two coats, the same as in the stomach; its action is to contract the bowels, giving them motion to convey the food along through them. The mucous coat is a continuation of the mucous coat of the stomach. Along this coat are found small glands known as villi lacteal; these absorb the nourishment from the food as it passes along through the bowels and pours it into the blood. The small intestines or bowels are attached on the upper side to what is known as the mesentery, which is attached above to the roof of the abdominal cavity. It can be seen in any of the smaller animals upon examination. About six inches from the stomach, in the bowels, are found two openings. One of these receive the hepatic duct, a tube for the purpose of carrying the bile from the liver to be poured in on the food as it passes through the bowels. The other opening is for the duct of the gland known as the pancreas. It secretes a clear fluid known as the pancreatic juice. These juices act on the food in the first part of the small intestines, changing it into chyle. After this, the action of the rest of the intestines is to absorb the nourishment out of the food as it is passing back. The small intestines and stomach, when in a healthy condition, should be found empty one hour after food has been eaten. The small bowels or intestines are situated mostly on the left side just behind the stomach.

The large bowels have three coats, the same as the small ones. The first part of the large bowels is known as the blind bowel or caecum, and is about three feet in length; this is generally the first thing to protrude when opening a horse’s abdominal cavity. Its use is to act as a reservoir to hold the water and fluid of the food; from this organ the water and fluid parts are mostly taken up into the system. The next part of the large bowels is known as the large colon; it lays along the floor of the abdominal cavity, is about nine feet in length and is doubled on itself three times. In this bowel the solid part of the food is found. Here digestion is brought about by the contraction and expansion of the muscles of the bowel and the nourishment taken from it, after which it is worked back out of this bowel and enters what is known as the floating colon. This is about ten feet in length and about two inches in diameter, or double the size of the small bowel. It is thrown into folds or pleats, and as that portion of the food containing no nourishment passes through it is worked into balls which pass back and are emptied into the rectum or back bowel. This is situated at the back part of the abdominal and pelvic cavity back of the small bowels or intestines and like them, is suspended by a fold paritoneum.

The rectum or back bowel is sometimes known as the straight bowel. It is about 18 inches long and forms the last part of the bowels or intestines. Its coats are a continuation of those of the large bowel, but each is thicker and heavier. Above this bowel are the bones of the sacrum, below it, in the horse the bladder and other small glands. Below the rectum of the mare are situated the womb and the vagina, the latter being the passage into the womb from the outside. The bones which help to form the pelvic cavity are situated at the sides, and at the back immediately under the tail is what is known as the annus. The use of the rectum is to hold the balls as they pass back from the floating colon. When the rectum becomes so full that there is pressure on the sides of the wall thus stimulating the nerves the muscular coat contracts and forces the contents back towards the annus. At the same time the muscles of the annus dilate, causing the faeces to pass out.

Accessory Organs of Digestion.—In the abdominal region these organs are the Liver, the Pancreas, and the Spleen.

The Liver is the largest gland in the body and is situated between the stomach and the diaphragm. The liver of the horse weighs from ten to twelve pounds. It is of a dark brown color, well supplied with blood and nerves, and is held in place by several strong ligaments. A bitter, greenish colored fluid called the bile is secreted from the liver and emptied into the digestive system, where it plays an important part in its action on the food. There is no gall bladder in the horse, but simply a tube passing from the liver to the small bowel into which it empties the bile about six inches back of the stomach. It is important to note that it is in this tube that gall stones sometimes collect.

The Pancreas is another very important gland. It is of a grayish, fatty color, and may be found near the roof of the abdominal cavity in front of the kidneys. The Pancreas secretes a clear, colorless fluid called the pancreatic juice. This fluid, like the bile from the liver, also plays an important part in the digestion of food. It is carried down from the Pancreas by a duct or tube emptying into the small bowel just back of that of the liver.

The Spleen is a long, flat gland about fifteen inches in length, situated along the left side of the stomach and to which it is closely attached. It is of a grayish red color and feels quite soft. It is ductless, there being no secretion passing from it. The function of this gland is not clearly understood, but by many it is supposed to regulate the temperature of the stomach during the process of digestion and to act as a reservoir for the blood. Some speak of it as the burying ground of the red corpuscles. It is well supplied with blood vessels and nerves and weighs about two pounds in an average sized horse.

RUMINANTIA.

Digestive System.—The lips of an ox are thick and hard. The upper has no hair on it and varies in color with the color of the animal. When cattle are in good health this space is always moist.

The cheeks on the inside are covered by many small rough processes, which give them a very rough appearance.

The Tongue of the ox is stronger than that of the horse and is more movable. It is very thick and heavy at the back, pointed at the front end and the upper part of it is very rough. It is by means of the tongue that the ox takes most of the food into the mouth.

The Salivary glands are similar to those of the horse.

The Teeth differ very much from those of the horse.

The ox has no front teeth in the upper part of his mouth, their place being taken by a pad of cartilage or gristle. This pad takes the place of the upper row of front teeth. The lower row of teeth press against it when the animal is cropping grass. This accounts for the fact that cattle do not do as well on short grass as horses.

The front teeth in the lower jaw also differ from those of the horse. They are eight in number, chisel-shaped, and are loosely set in the gum.

The molars, or back teeth, are similar to those of the horse, only they are smaller and not so smooth on their upper surface. The ox has twenty-four molars or back teeth, and eight incisors or front teeth, making thirty-two in all.

The Gullet of the ox is much larger than that of the horse.

The Oesophagus or tube, which carries the food down from the mouth to the stomach is well developed, the fibers in it being very strong and possessing a double action. When the animal is eating they carry the food from the mouth to the stomach, and when chewing the cud they act the very opposite, carrying the food from the stomach back into the mouth.

The Stomach.—The student will do well to give some time to the study of this important organ of the ox, as it is very frequently the seat of disease.

The stomach has a capacity of fifty-two gallons and is divided into four separate and distinct compartments: the Rumen or Paunch, the Reticulum or Honey Comb, the Omasum or Many-plies, and the Abomasum or the true Stomach. In the first three of these the food undergoes a sort of preparatory process, while in the fourth the process of digestion is complete.

The Rumen or paunch is very large, and in an aged animal fills three-quarters of the abdominal cavity. It lies up against the left side of the wall of the abdomen, where it is attached and held to its place by the ligaments. Its situation being an important matter, as many diseases of the rumen, or paunch, are first noticed on the left side. Tapping for bloating is always done on the left side because of this fact. The walls of the paunch of an ox resemble those of the stomach of the horse, but are not so sensitive, and stand a great deal of abuse before inflammation sets in. The paunch has two openings, both of which are at the front; through one the food enters, while through the other it passes out into the next division.

The Reticulum, or honey comb, is the smallest division and resembles a honey comb in appearance. This part has little to do with preparing the food. It is provided with two openings, one in front, where the food enters, the other at the back, where it passes through into the third division. In the reticulum, or honey comb, the food is softened further by the water that the animal drinks which passes directly into the second division. The food is here pressed into balls and prepared to be forced back into the mouth to be further masticated.

The Omasum, or many-plies, is the second largest division of the stomach. When full it is ovoid in shape. It is placed just behind the second division and at the right side of the paunch. The inside is full of folds, or layers of membrane, into which all the coarse parts of the food pass and roll about until it is fine and well prepared to pass into the last division. When this part of the stomach becomes deranged and the food becomes dry and hard between the folds, the disease called impaction of the many-plies, or dry murrain, is the result.

The Abomasum, or fourth stomach, is the true digestive part. In it the food is completely digested. The walls are redder in color than those of the three first divisions and contain the glands which secrete the acids and gastric juices. This stomach has two openings, one through which the food enters and the other through which it passes into the small bowels.

The Bowels, or intestines, of the ox are divided into large and small bowels. This, together with their structure and action resembles that of the horse. The small bowels are only half the size of the horse, being about one-half inch in diameter, and about one hundred and fifty feet in length. The large bowels are not nearly so long as those of the horse and are thirty-five feet in length.

The Liver of the ox resembles that of the horse, except that it is provided with a gall bladder which resembles a pear in shape. This acts as a sac in which to store the gall during the time it is not required in digestion. When digestion is going on the wall of the gall sac contracts and forces the gall down to the food. The other glands, the pancreas and spleen, resemble those of the horse. The juices from these glands have the same action in cattle as they have in the horse.

Rumination, or Chewing the Cud.—Food when first taken into the mouth of a ruminant is but lightly masticated and mixed with the saliva from the salivary glands, after which it is swallowed, passing through the oesophagus into the rumen or paunch (first stomach). This division acts as a reservoir or storehouse for food thus eaten quickly. When the animal has time, so to speak, he lies down or stands quietly and completes the process of mastication of his food by chewing the cud. This peculiar act is performed as follows: After being softened and moistened by warmth, the food passes from the rumen or paunch into the second division—the reticulum, honey comb or second stomach. In this small globe-like compartment the food is moistened and compressed into pellets—the cud. By a peculiar reverse action of the oesophagus or gullet these pellets are taken back into the mouth for further mastication or chewing. When re-mastication is completed it is again swallowed, but this time it passes directly into the omasum, many-plies or third stomach, and thence to the fourth or true stomach.

Process of Digestion After Rumination.—Following rumination which, strictly speaking, is the first step in the digesting process, the food passes into the third stomach. The fine parts pass right along to the fourth stomach while the coarser parts are drawn between the folds of the membrane in this division and worked about until it is fine and ready to pass into the fourth stomach, where it becomes fully digested by the action of acids and gastric juices which are secreted in this part. It then passes into the small bowels, and is acted upon by the bile from the liver and the pancreatic juice from the pancreas. These juices are emptied into the first part of the small bowels through little ducts or tubes, which lead from the glands down to the bowels, just on the same principle as that of the horse. After this, throughout the rest of the bowels, the nourishment of the food is taken into the system by means of little glands which are situated in the coating of the bowels. The nourishment when once in the blood goes to supply the different parts of the body, while the part containing no nourishment or undigested passes off through the back bowels in the form of feces.

TEETH.

Teeth are objects situated in the upper and lower jaws. They are made of the same tissues as bone but contain 10¹/₂ per cent. more of earthy salts. This fact accounts for their extreme hardness. Unlike bone they can stand exposure to air and friction without becoming diseased. Teeth are used to masticate or chew the food, and because of the constant change in their formation and appearance they serve as a guide in telling the age of the horse.

There are three hard structures that enter into the formation of the teeth—Dentine or Ivory, Enamel, and Cementum, or Crusta Petrosa.

The Dentine, or ivory, is situated in the upper part around the pulp or nerve cavity. It is of yellowish color and largely supplied with nerves which pass through it from the pulp cavity.

The Enamel is the hardest substance of the tooth, and covers the outside of all the exposed part. This substance is characterized by its whiteness and, unlike the dentine, contains no blood vessels or nerves. If part of the enamel is broken off it is never replaced, and the tooth below the broken part generally becomes decayed.

The Cementum, or crusta petrosa, is found in the fang or root and the parts situated below the gum. It is the softest part of the tooth.

Teeth may be simple or compound. Simple as in the dog, where the entire exposed surface is covered by a solid cap of enamel, which alone is in wear; compound or complex, as in the horse, where various tissues are in wear. A tooth consists of the following anatomical parts: The body, or crown, that part above the gum; the table, the part that comes into wear on the top; the neck, the part to which the gums are attached; and the fangs or roots, the parts situated down in the bone.

There are three kinds of teeth found in the horse, the incisors, the canine and the molars.

The Incisors, or front teeth, situated in the front part of the mouth just inside the lips, are twelve in number, six above and six below.

The Canine, or bridle teeth, are often absent in the mare. They are four in number, two in the upper and two in the lower jaw, one on each side about two inches back from the incisor teeth. They are from a quarter to three-quarters of an inch above the gum, are round and pointed and of no particular use. They resemble the eye teeth of other animals.

The Molars, or back teeth, are twenty-four in number, six on each side in the upper and six on each side in the lower jaw. With these the food is ground and masticated.

Wolf Teeth are two small, round, pointed temporary teeth which vary in size in different animals, situated one on each side in front of the molars or back teeth in the upper jaw.

Temporary and Permanent Teeth.—The horse has two sets of teeth. The milk are temporary and are those that the colt sheds; while those that come in and remain without being shed are called the permanent teeth. The cutting of the teeth of the foal varies, but at or within nine days after birth he has four front teeth, two in the center above and two below, and in the back part of the mouth twelve molars. At from seven to nine weeks four more incisors or front teeth appear, one at each side of the two center teeth in each jaw. At nine months he gets the last of his milk or temporary teeth, these being the corner teeth, two in the upper side and two in the lower side of the jaw. At this time he has his full set of milk temporary teeth, consisting of twelve molars or grinders and twelve incisors or front teeth, six above and six below, making twenty-four in all. As the colt advances in age he sheds all these teeth. He then commences to get permanent teeth. When the age of one year is reached, four permanent molars appear, two in each jaw, one on each side, behind the three temporary teeth. At two years of age he gets four more back molars, one on each side of each jaw. When the age of two years and nine months is reached the two middle teeth of the temporary incisors, or front teeth of each jaw fall out, and are replaced by two permanent incisors in each jaw; thus at the age of three years these four permanent incisors are up and in wear. At this age, the first eight molars, two on each side of each jaw, are shed and replaced by eight permanent molars. At four years of age he sheds four more front or incisor teeth next to those shed at three years, and these are replaced by four more permanent incisors or front teeth. At this age, too, he sheds the four remaining temporary molars, or grinders, which are replaced by four more permanent molars. He also gets four more permanent molars at the back of the mouth. Thus at the age of four years the colt has a full set of permanent molars, consisting of six on each side of each jaw, making twenty-four in all. At five years of age he sheds the four remaining temporary incisors or front teeth, which are replaced by four permanent incisors, known as the corner teeth. It is important to become familiar with the time at which the colt sheds his different teeth, for sometimes the caps or shells of the teeth do not fall off when they should. These should be watched, for they greatly interfere with feeding and should be removed with forceps. At five years of age the canine or bridle teeth make their appearance; thus at the age of five years the colt has all his teeth or what is known as a full mouth.

The following table shows the various changes taking place in the mouth of the horse from the time of birth up to the age of five years:

Hence the horse has—

RUMINANTS

RESPIRATORY SYSTEM OF THE HORSE.

Organs of Respiration.—By the action of these organs certain chemical and physical changes take place in the blood, the chief of these consisting of absorption of oxygen from, and giving off carbonic acid to the atmospheric air, the former change being necessary for the elaboration of the fluid, the latter for the elimination of a substance which, if retained, would prove injurious. The organs of respiration are invariably adapted to the wants of the animal and the medium in which it lives. Thus insects breathe by air-tubes, opening on the surface of the body; in the oyster breathing is performed by fringes; in fishes by gills; in the mammalia by means of elastic air-receptacles, called lungs, which are enclosed in special cavities, and communicate with the atmosphere by means of an air-tube.

In the horse, who breathes only through his nose, the organs of respiration are the nostrils, nasal-chambers, larynx, trachea, and in the thoracic cavity, the bronchi, bronchial tubes, and the lungs.

Nostrils.—The nostrils are two openings, one on each side of the nose. They are held open by the aid of cartilage and muscles. About one and one-half inches up the nostril on the under side is a small opening about the size of a grain of shot. Through this opening the duct or tube which carries the tears down from the eyes empties into the nose. The nostril is lined with a thin, delicate skin which changes into mucous membrane as it passes up into the chambers of the head.

Nasal Chambers.—These give passage to the air from the nostril into the larynx. There are two of these chambers, divided in the center by a thin partition or cartilage called the septum nasi. These communicate with the sinuses of the head. The horse cannot breathe through the mouth on account of the formation of the throat, and this compels him to always breathe through the nostrils. This is a point which should be remembered.

Larynx.—This is a cavity made of cartilage. It gives passage to the air and also the organ of voice. It is situated in the floor of the gullet. This cavity has an opening on its upper side, guarded by a valve, which is always opened except when the animal is swallowing food or water. When the food is being swallowed it passes over the valve which closes the opening while the food passes over it. This is important, for if the valve does not close properly, thus allowing either food or water to drop into the windpipe, the animal will have a fit of coughing. This is sometimes referred to as “the food going down the wrong way.” On the outside of this cavity of cartilage are found several small muscles which help to hold it in its place. It is lined inside by a continuation of the same membrane as that of the chambers of the head. The vocal cords which come into play when the animal is whinnying are found along the inside of this cavity. These cords are not nearly so well marked as in the human being, and if they or the cartilage of the larynx become affected it generally gives rise to the disease called wind-broken or roaring.

Trachea (Windpipe).—This is a tube which conveys the air down from the larynx to the bronchial tubes in the lungs. It is made up of forty or fifty rings of cartilage which are united to each other by strong elastic ligaments. They give to the windpipe its flexibility, that is, the power to bend in any direction almost like a piece of elastic. From the larynx the windpipe enters the chest where it terminates into two small tubes, one going to the right lung and one to the left. These are called the bronchial tubes.

Bronchial Tubes and Air Cells.—These are made up of the same material as that of the windpipe, but are only about half the size. After passing into the substance of the lungs they break up into small tubes which pass all through the lungs and terminates into what is known as the air-cells. These small tubes and air cells are lined inside by a very thin mucous membrane, a continuation of the membrane lining the other organs already mentioned. Just inside this thin mucous membrane is found the capillary network of the lungs, and while the blood is slowly passing through this network of vessels it gives off to the air in the air cells carbonic acid gas and takes in the oxygen from the pure air while it is in the lungs.

Lungs.—Lungs are the most important organs of respiration. They are spongy, yellowish organs, two in number, one situated on the right side, and the other on the left. The right lung is the largest because of the left one having a hollow in its side for the heart. The lungs are separated by a partition known as the mediastinum, by the heart which is in the folds of this partition, and also the large blood vessels and oesophagus. They are made up of light elastic tissue and are full of air cells and tubes. While the animal is alive they are very large and fill up nearly the whole chest cavity, but after death they collapse and are not nearly so large. Between the lungs and the ribs is found a serous membrane called the pleura or the lining membrane of the chest. It is made up of two folds, one being attached around the outer surface of the lungs, while the other is attached to the ends of the ribs at the side and at the back to the large curtain which separates the lungs from the bowels. The little glands situated in this membrane secrete an oily fluid which serves to lubricate these parts while the lungs are working in the chest so as not to cause friction. When this membrane becomes inflamed from a chill or injury it sets up the disease called pleurisy.

Respiration.—The number of respirations per minute varies with the different classes of animals; as a rule, the larger the animal the slower the respiration.

The rate of breathing is increased from the process of digestion immediately after eating, or may increase from exercise.

RESPIRATORY SYSTEM OF THE OX.

The nostrils are narrow and capable of little dilation compared to those of the horse. The nasal chambers differ chiefly in there being an additional turbinated bone. The nasal chambers communicate with the mouth, therefore cattle can breathe through the mouth to a certain extent. The larynx is simpler in construction, the true vocal cords being only slightly developed. The trachea or windpipe presents no important variation. We may note the presence of a third bronchus, which passes to the right lung to supply a lobe which is wanting in the horse.

The Thoracic Cavity is relatively smaller in the ruminants, and the pleurae present a very important deviation from the arrangement found in the solipede—viz., the back or posterior mediastinum is imperforate and strong, completely separating one pleural sac from the other. This arrangement exists in all the domesticated mammals but the solipede. The left lung is divided into two lobes, the right into four, the front one recurving over and almost covering the front of the heart. The interlobular or cellular tissue is exceedingly thick, the separation between the lobules being distinctly visible. This arrangement explains perfectly the special nature of pneumonic lesions in the large ruminants.

URINARY SYSTEM OF THE HORSE.

The organs of this system secrete the urine from the blood, and excrete or expel it from the body. These organs are chiefly the kidneys, ureters, bladder and urethra. The urine, which is a watery fluid, is secreted by the kidneys, and carried off by their ducts, the ureters, to a special reservoir, the bladder, where it accumulates and from which it is finally expelled at intervals through the urethra.

The kidneys are two compound tubular glands, one on the right side and one on the left side, and are situated just below the small of the back (sublumbar region), the right one being the fartherest ahead. In shape they are long and narrow and resemble the liver in color. In cutting one of the kidneys open, it is found to be full of glands and tubes, which secrete the urine from the blood while it is passing through the kidneys. These tubes pass to the center of the kidneys, where they empty the urine into what is called the pelvis. The glands are largely supplied with blood vessels and nerves. The use of the kidneys are to secrete the urine from the blood, which contains a large amount of what is known as ureaic acid, and if not taken out of the blood by these glands, acts as a poison to the system.

The Ureters are tubes which carry the urine down from the pelvis of the kidney to the bladder. They are two in number, one situated on the right side of the pelvic cavity and the other on the left side, close to the walls—they enter on each side at the upper surface of the bladder. They are only about one-sixteenth of an inch in diameter.

The Bladder is situated in the pelvic cavity. When it is full it sometimes stretches out into the abdominal cavity. It consists of a body and neck. The body is the large part, and is placed in front; the neck being at the back part of the bladder. This is where the urine passes out of the bladder. The bladder is made up of three coats, somewhat similar to that of the bowels. The serous coat is a continuation of the serous coat found in the abdominal cavity lining the bowels. The inside is lined with mucous membrane which is thrown into folds when the bladder is empty. Another coat is found between the two membranes above mentioned, called the muscular coat, the action of which is to contract the bladder when the animal wants to urinate. The bladder is held in by ligaments. The rectum lies above the bladder, which in the horse rests on the floor of the pelvic cavity. Its position in the mare differs from that of the horse. Instead of the rectum or back bowel being immediately above it, as in the horse, the womb is just above the bladder or between it and the rectum. The bladder acts as a reservoir in which to store the urine until it is full; it then presses on the walls and nerves, giving a peculiar sensation to these parts, causing the walls to contract, forcing the urine into a tube which carries it from the body. This is called the urethra. The neck of the bladder is simply an opening at the back part, and is guarded by a valve which prevents the urine from dripping out except when the animal is passing its urine or water.

The Urethra is the tube which carries the urine from the bladder out of the body. It is situated much differently in the mare than in the horse. In the mare it is very short, passing from the neck of the bladder along below the womb and vagina, which is the passage from the outside into the neck of the womb. It opens up into the underside of this passage about four inches in from the outside. This opening is guarded by a small, thin valve, and can be felt by passing the finger along the under side of the passage which leads into the womb. In the horse this tube is a great deal longer than in the mare. It commences at the bladder, passes along below the rectum or back bowel to just below the anus. Here this tube bends downward and forward and passes into the penis, continuing down to the end where it terminates. Its purpose is to carry the urine from the bladder out of the body and to perform certain actions in connection with the genital organs. Its lining is a continuation of the membrane of the bladder.

URINARY ORGANS OF THE OX.

The chief difference in these organs occurs in the kidneys, which in the ox are larger, and in place of being smooth, like those of the horse, are rough, resembling a bunch of grapes. The bladder and the urinary organs resemble those of the horse.

GENERATIVE SYSTEM OF THE HORSE.

Animals possess the faculty of reproducing or propagating their species, and this function may be non-sexual or sexual, the former being confined to certain lowly-organized classes of animals.

In all the higher animals the generation of a new being is dependent upon two individuals, a male and a female, the female furnishing a germ, or ovum, the male a fecundating fluid, or sperm, which animates the germ and renders it fit for development.

Both the ovum of the female and the sperm of the male are secretions of glands, which are termed the genital glands, male and female; and in either sex the generative system may be said to consist of these glands, with certain accessory organs. The act of coition brings the two secretions into contact.

We have two systems of genital organs to consider—the male and the female.

Male.—The genital organs of the horse are as follows: The scrotum or bag, the testicles, the spermatic cord, the vesiculae seminales or pouches which hold the semen or sperm, the urethra, the penis and the sheath.

The Scrotum is a sac or bag which contains the testicles. It is situated between the hind legs, and is covered on the outside by a very fine, soft skin. Passing up in the center under the sheath the scrotum is a well marked line in the skin called median raphe. This can be plainly seen when the horse is on his back. It continues up, gradually getting fainter until it reaches the anus. Under the skin are layers of white fascia or tissue which can be seen by cutting through the scrotum. There is a partition in the scrotum separating the two testicles. The size of the scrotum is affected very much by the weather. In cold weather its fibres contract, causing it to get very much smaller, while in warm weather the fibres relax, causing it to become very much larger. The scrotum contains, supports and protects the testicles.

The Testicles are the glands which secrete the semen or sperm. They are two in number, one situated on the left side and the other on the right. They are oval in shape, and are attached above to the spermatic cord. Before the animal is born the testicles are situated in the abdominal cavity and attached to the serous membrane which has already been spoken of in connection with that cavity. At or about the time of birth, there takes place what is known as the descent of the testicles into the scrotum. In their downward course they pass through a slit or small opening at the back part of the muscles of the abdomen, where they are attached to the under part of the hip bone. These slits or openings are known as the inguinal rings. They can be felt in the horse by pressing the fingers well up into the groins. The descent of the testicles is an important point to remember. If the testicle does not descend into the scrotum the horse is known as a ridgling. In this case the testicle is not found in the scrotum. At the front part of the testicle there is a small ridge called the globus major and at the back of it is another smaller ridge called the globus minor. Passing between these two ridges is another well marked ridge called the epididymis. These can be easily seen by examining the testicle after the animal is altered or castrated. The substance of the testicle is made up of small glands and fine tubes.

These tubes, as they pass towards the back of the testicle, form into larger tubes and finally unite to form one called the vas deferens.

The Spermatic Cords, or the cords of the testicles, are attached above to the inguinal rings or openings mentioned before. They are about five or six inches long and have the testicles attached to them below. In each cord is found a small muscle which goes by the name of the spermatic muscle, the rest of the cord being made up of the spermatic artery, veins and nerves. Running up at the back of these cords is found a tube called the vas deferens. Around the spermatic cords and testicles is a serous membrane, one layer being attached to the testicle and cord, while the other is closely attached around the inside of the scrotum. In this membrane are small glands which secrete an oily fluid to lubricate the parts, preventing friction when they are jolted about in the scrotum. This fluid flies out as soon as the scrotum is cut. This is important, because sometimes from a slight injury the glands will secrete a large amount of this fluid, thus causing the scrotum to look large and swollen. This disease is known as hydrocele or water in the scrotum.

Vas Deferens.—These tubes are two in number and are situated just behind the spermatic cords. They are about an eighth of an inch in diameter and quite hard. They carry the semen up the back part of the spermatic cord through the inguinal rings, before mentioned. They pass backward and upwards, one on each side, to the upper part of the bladder, where they empty into two small pouches or sacs, called the vesiculae seminales. These store up the semen as it is secreted by the testicles, and when full present the appearance of a pear.

Vesiculae Seminales.—These sacs or pouches are situated at the upper side, over the neck of the bladder, one on each side. They have the vas deferens emptying into them at the front end, while at the back end of each is a small opening that leads out into another small tube which passes backward and empties into the urethra, mentioned before as carrying the urine out from the bladder. These sacs or pouches store up the semen or sperm of the horse. During sexual intercourse, these pouches contract and force the semen through the little tubes mentioned out into the urethra, leading down through the penis.

The Penis is the main organ of sexual intercourse. Its substance is formed of what is known as erectile tissue, which under certain circumstances becomes enormously distended with blood. Passing up the under side there is, what has already been mentioned, the urethra, or the tube, which carries the urine out of the body, and also in the act of intercourse carries the semen. This is used for two purposes, as we have already mentioned.

The Sheath is a loose process of skin which passes downward from the scrotum, generally from about five to six inches, according to the size of the animal. It is attached to each side, leaving a hole or opening in the center through which the penis passes. The outside of the sheath is covered by a thin, delicate skin similar to that of the scrotum. It is lined inside by a membrane containing many small glands, which secrete a thick, dark fluid to lubricate this passage. Sometimes this fluid collects in here and has the appearance of tar. This is important, for when it collects to a large extent the sheath should be washed.

The Semen or sperm of the horse is a light fluid, which, when examined under a microscope is found to contain small objects called spermatozoa. These move about, and when in the womb meet the ovum of the female, which is secreted by a gland called the ovary. When these two small objects unite, they form the foetus, or what may be called the animal in its first stage of development.

FEMALE GENITAL ORGANS.

The female genital organs, or the organs of the mare, are very much different from those of the horse. They are known as follows: The ovaries, the fallopian tubes, or tubes which carry the ovum from the ovaries to the uterus or womb, the uterus or womb, the vagina, and the vulva.

The Ovaries in the mare correspond to the testicles in the horse. Each is about the size of a pigeon’s egg, and resembles it much in shape. They are held in place by ligaments, and at the back part are provided with tubes leading from them called the fallopian tubes. The ovaries secrete the ovum or germ. This is a very minute body, which, when examined under the microscope, is found to be only 1-150 of an inch in diameter.

The Fallopian Tubes are two canals, one on each side. They pass backward and upward, and enter the front part of the uterus or womb. These small tubes are simply used to carry the germ or ovum up from the ovaries and empty into the uterus or womb.

The Uterus or Womb is a muscular sac situated in the pelvic cavity, bounded above by the rectum, below by the bladder, and on either side by the walls of the pelvic cavity. It is divided into what is known as a body and a neck. The body of the womb is very small, being only about four to six inches in length and a couple of inches in diameter when the animal is not pregnant. Near the front end, at the upper side there are openings by which the ovum enters. When the animal becomes pregnant, the body of the womb becomes enlarged and passes forward and to the left side of the abdominal cavity. It continues to enlarge as the time of pregnancy passes on, until the foetus, or young, has attained its full size. After the mare has had her young, the womb begins to get smaller until it attains its natural size again. The womb is very largely supplied with blood vessels and nerves. This is especially so when the animal is pregnant, as it takes a large amount of blood to nourish the foetus, or the young animal, before birth. It is made up of three coats. The inner is called mucous membrane, and in the mare, while pregnant, is covered with numerous processes about the size of peas to which the placenta or after-birth of the foal is attached. The muscular coat is next to that of the mucous coat, and lies between the outer and inner coats of the womb. It is made up of muscular fibres, and is strong and thick in the womb, much thicker than it is in the bowels or other organs, already mentioned. This coat supports and protects the foetus, or young, while being carried in the womb, and at the time of parturition, or what is commonly known as foaling, this coat also comes in use. It contracts the womb very forcibly on the foal, while the neck of the womb lies open, thus helping to force the foal out of the womb. This is important as the contraction of this coat produces what is known as labor pains. Lying outside, and covering around the womb, is a serous coat, a continuation of the serous coat of the bowels. The womb is held in place by strong ligaments attached to the sides, and from there to the hip bones. These are called broad ligaments. At the back part of the womb is the neck. It consists of an opening, formed by a projection about the size of an egg. This has a hard, gritty feeling when the animal is not in season. The neck at this time is closed. The neck of the womb is under control of the muscle around it, and this muscle is under control of the nerves of the womb. When a mare comes in season this muscle is relaxed to a certain extent, thus allowing the neck to open wide enough for the passage of a couple of fingers. By working around it with the fingers at this period it can be forced wide enough to admit a man’s hand. If the mare is put to the horse at this time and becomes pregnant or with foal, the muscles in the neck of the womb contract, firmly closing it. It remains closed until the time of foaling. When, at the time of foaling, the labor pains come on, the muscle in the neck dilates, allowing the neck of the womb to open large enough for the foal to pass out. The neck of the womb can be felt easily by oiling the hand and passing it into the passage of the womb. It will be noticed, too, that the neck spoken of projects into the passage.

The Vagina and the Vulva.—These two organs together make up the passage which leads into the womb from the outside. In the young mare they are separated by a thin curtain, or partition, made up of mucous membrane. This curtain is found about four inches from the outside, and is known as the hymen. It is destroyed, or should be, when the mare is first put to the horse, although it is broken down other ways, and in some cases it will disappear of its own accord. The part of the passage in front of the hymen is called the vagina. This passage, in structures, resembles the womb, but is not so strong. There are numerous glands situated along the inner lining which secretes a fluid to lubricate it. The principle use of this organ is to guide the penis during sexual intercourse, and at the time of foaling serves as a passage for the foal. That part of the passage behind the hymen is known as the vulva. It is about four inches long and about two or three inches high, varying according to the size of the mare. In front, it is separated from the vagina by the hymen membrane. It resembles the vagina in structure and is also provided with little glands in its inner membrane to secrete fluid to lubricate the passage. At the back part of the vulva or around the outside is what is known as the lips of the vulva, one on each side of the opening. The outside of the lips is covered by a very fine skin. Just below the skin, they consist of erectile tissue, which is the same kind of tissue as that of the penis of the horse. This tissue is found more abundantly in the lips of the vulva of the young mare than in those of an old mare. The opening between these lips is situated just below the anus, or the opening where the back bowel ends. At the back part of the vulva, on the under side, is an opening, or hole, about large enough for the passage of a man’s finger. Through this hole the tube leading from the bladder enters into the passage and allows the urine to pass into the vulva, through which it runs out of the body. The clitoris is situated on the upper side of this passage, just inside the lips. It can be seen in the mare when she works the vulva after passing urine. Just below the clitoris are found two or three small glands which secrete the fluid that passes away when the mare is horsing.

Mammary Glands, or what is known as the mare’s udder or bag, are two in number, situated between the thighs. In the young mare they are very small, but after the mare is pregnant a few months these glands enlarge, until at foaling time they attain their largest size. They are covered outside by a thin, smooth skin. The substance of them consists of small glands and tubes retain or hold milk until it is drawn away from the bag either by milking or by the young animals sucking. During the time of suckling the young, the glands are largely supplied with blood, from which the milk is secreted. On the under side of each gland is found the teat, or that part taken hold of by the young when sucking. The end of the teat is pierced by several small holes, through which the milk passes.

GENITAL ORGANS OF THE BULL.

The testicles are ovoid in shape and well developed, its long axis being nearly vertical; the membrane which separate the two testicles is very strong.

The spermatic cord and artery are small compared with those of the horse.

The penis is long and pointed, and has an S-shaped curve in it just below the pelvic bones; this curve can be felt by feeling just behind the bag.

The sheath is long and runs further forward on the belly. It has a tuft of hair on the point of it. During the time the bull is serving the S-shaped part of the penis is straightened out by the action of the protracter muscles, and drawn back into the S-shaped curve by retractor muscles.

The urethra is completely enveloped by the fibrous sheath.

GENITAL ORGANS OF THE COW.

The ovaries of the cow are comparatively smaller than those of the mare, but resemble them in structure.

The uterus or womb of the cow somewhat resembles that of the mare, but the inner membrane is different, being covered with sixty or eighty mushroom-like bodies about the size of a pigeon’s egg, more flattened out. These bodies receive the name of cotyledons; to these the placenta or afterbirth is attached—a very important point with which every person interested should be familiar. These may be felt by examining a cow soon after calving. The passage from the womb of the cow is shorter than that of the mare, but is formed on the same principles.

The mammary glands constitute an organ termed the udder, which is composed of two symmetrical halves, placed one against the other. Each half is again divided into two distinct glands, each with its own teat, so that the udder consists of four mammae and four teats; behind this there may be two small rudimentary teats. In the center of each quarter, just at the base of the teat, is a large cavity, the general receptacle of all the milk ducts. From this cavity, which is sometimes large enough to contain a quart, proceeds down the center of the teat one defined canal from which the milk is drawn.

In the small ruminants as the sheep and goat there are two mammae and two teats, constructed like those of the cow.