64. The bones are firm and hard, and of a dull white color. In all the higher orders of animals, among which is man, they are in the interior of the body, while in lobsters, crabs, &c., they are on the outside, forming a case which protects the more delicate parts from injury.

65. In the mechanism of man, the variety of movements he is called to perform requires a correspondent variety of component parts, and the different bones of the system are so admirably adapted to each other, that they admit of numerous and varied motions.

66. When the bones composing the skeleton are united by natural ligaments, they form what is called a natural skeleton, when united by wires, what is termed an artificial skeleton.

67. The elevations, or protuberances, of the bones are called proc´es-ses, and are, generally, the points of attachment for the muscles and ligaments.

68. The BONES are composed of both animal and earthy matter. The earthy portion of the bones gives them solidity and strength, while the animal part endows them with vitality.

64. What is said of the bones? 65. Is there an adaptation of the bones of the system to the offices they are required to perform? 66. What is a natural skeleton? What an artificial? 67. What part of the bones are called processes? 68–73. Give the structure of the bones. 68. Of what are the bones composed? What are the different uses of the component parts of the bones?

Experiments. 1st. To show the earthy without the animal matter, burn a bone in a clear fire for about fifteen minutes, and it becomes white and brittle, because the gelatin, or animal matter of the bone, has been destroyed.

2d. To show the animal without the earthy matter of the bones, immerse a slender bone for a few days in a weak acid, (one part muriatic acid and six parts water,) and it can then be bent in any direction. In this experiment, the acid has removed the earthy matter, (carbonate and phosphate of lime,) yet the form of the bone is unchanged.

69. The bones are formed from the blood, and are subjected to several changes before they are perfected. At their early formative stage, they are cartilaginous. The vessels of the cartilage, at this period, convey only the lymph, or white portion of the blood; subsequently, they convey red blood. At this time, true ossification (the deposition of phosphate and carbonate of lime) commences at certain points, which are called the points of ossification.

70. Most of the bones are formed of several pieces, or centres of ossification. This is seen in the long bones which have their extremities separated from the body by a thin partition of cartilage. It is some time before these separate pieces are united to form one bone.

71. When the process of ossification is completed, there is still a constant change in the bones. They increase in bulk, and become less vascular, until middle age. In advanced life, the elevations upon their surface and near the extremities become more prominent, particularly in individuals accustomed to labor. As a person advances in years, the vitality diminishes, and in extreme old age, the earthy 31 substance predominates; consequently, the bones are extremely brittle.

How can the earthy matter of the bones be shown? The animal? 69. What is the appearance of the bones in their early formative stage? When does true ossification commence? 70. How are most of the bones formed? 71. What is said of the various changes of the bones after ossification?

72. The fibrous membrane that invests the bones is called per-i-os´te-um; that which covers the cartilages is called per-i-chon´dri-um. When this membrane invests the skull, it is called per-i-cra´ni-um.

73. The PERIOSTEUM is a firm membrane immediately investing the bones, except where they are tipped with cartilage, and the crowns of the teeth, which are protected by enamel. This membrane has minute nerves, and when healthy, possesses 32 but little sensibility. It is the nutrient membrane of the bone, endowing its exterior with vitality; it also gives insertion to the tendons and connecting ligaments of the joints.

72. What is the membrane called that invests the bones? That covers the cartilage? That invests the skull? Explain fig.6. 73. Describe the periosteum.

74. There are two hundred and eight[3] bones in the human body, beside the teeth. These, for convenience, are divided into four parts: 1st. The bones of the Head. 2d. The bones of the Trunk. 3d. The bones of the Upper Extremities. 4th. The bones of the Lower Extremities.

75. The bones of the HEAD are divided into those of the Skull, Ear, and Face.

76. The SKULL is composed of eight bones. They are formed of two plates, or tablets of bony matter, united by a porous portion of bone. The external tablet is fibrous and tough; the internal plate is dense and hard, and is called the vit´re-ous, or glassy table. These tough, hard plates are adapted to resist the penetration of sharp instruments, while the different degrees of density possessed by the two tablets, and the intervening spongy bone, serve to diminish the vibrations that would occur in falls or blows.

77. The skull is convex externally, and at the base much thicker than at the top or sides. The most important part of the brain is placed here, completely out of the way of injury, unless of a very serious nature. The base of the cranium, or skull, has many projections, depressions, and apertures; the latter affording passages for the nerves and blood-vessels.

74. How many bones in the human body? How are they divided? 75–81. Give the anatomy of the bones of the head. 75. How are the bones of the head divided? 76. Describe the bones of the skull. 77. What is the form of the skull? What does the base of the skull present?

78. The bones of the cranium are united by ragged edges, called sut´ures. The edges of each bone interlock with each other, producing a union, styled, in carpentry, dovetailing. They interrupt, in a measure, the vibrations produced by external blows, and also prevent fractures from extending as far as they otherwise would, in one continued bone. From infancy to the twelfth year, the sutures are imperfect; but, from that time to thirty-five or forty, they are distinctly marked; in old age, they are nearly obliterated.

79. We find as great a diversity in the form and texture of the skull-bone, as in the expression of the face. The head of the New Hollander is small; that of the African is compressed; while the Caucasian is distinguished for the beautiful oval form of the head. The Greek skulls, in texture, are close and fine, while the Swiss are softer and more open.

78. How are the bones of the skull united? What are the uses of the sutures? Mention the appearance of the sutures at different ages. What does fig.7 represent? 79. What is said respecting the form and texture of the skull in different nations?

80. In each EAR are four very small bones. They aid in hearing.

81. In the FACE are fourteen bones, some of which serve for the attachment of powerful muscles, which are more or less called into action in masticating food; others retain in place the soft parts of the face.

82. The TRUNK has fifty-four bones—twenty-four Ribs; twenty-four bones in the Spi´nal Col´umn, (back-bone;) four in the Pel´vis; the Ster´num, (breast-bone;) and the Os hy-oid´es, (the bone at the base of the tongue.) They are so arranged as to form, with the soft parts attached to them, two cavities, called the Tho´rax (chest) and Ab-do´men.

80. How many bones in the ear? 81. How many bones in the face? What is their use? Explain fig.8. 82–94. Give the anatomy of the bones of the trunk. 82. How many bones in the trunk? Name them. What do they form by their arrangement?

83. The THORAX is formed by the sternum in front; the ribs, at the sides; and the twelve dorsal bones of the spinal column, posteriorly. The natural form of the chest is a cone, with its apex above; but fashion, in many instances, has nearly inverted this order. This cavity contains the lungs, heart, and large blood-vessels.

84. The STERNUM is composed of eight pieces in the child. These unite and form but three parts in the adult. In youth, the two upper portions are converted into bone, while the lower portion remains cartilaginous and flexible until extreme old age, when it is often converted into bone.

85. The RIBS are connected with the spinal column, and increase in length as far as the seventh. From this they successively 36 become shorter. The direction of the ribs from above, downward, is oblique, and their curve diminishes from the first to the twelfth. The external surface of each rib is convex; the internal, concave. The inferior, or lower ribs, are, however, very flat.

83. Describe the thorax. Explain fig.9. 84. Describe the sternum. 85. Describe the ribs.

86. The seven upper ribs are united to the sternum, through the medium of cartilages, and are called the true ribs. The cartilages of the next three are united with each other, and are not attached to the sternum; these are called false ribs. The lowest two are called floating ribs, as they are not connected either with the sternum or the other ribs.

87. The SPINAL COLUMN is composed of twenty-four pieces of bone. Each piece is called a vert´e-bra. On examining one of the bones, we find seven projections, called processes; four of these, that are employed in binding the bones together, are called articulating processes; two of the remaining are called the transverse; and the other, the spinous. The last three give attachment to the muscles of the back.

88. The large part of the vertebra, called the body, is round and spongy in its texture, like the extremity of the round bones. The processes are of a more dense character. The projections are so arranged that a tube, or canal, is formed immediately behind the bodies of the vertebrÆ, in which is placed the me-dul´la spi-na´lis, (spinal cord,) sometimes called the pith of the back-bone.

89. Between these joints, or vertebrÆ, is a peculiar and highly elastic substance, which much facilitates the bending movements of the back. This compressible cushion of cartilage also serves the important purpose of diffusing and diminishing the shock in walking, running, or leaping, and tends to protect the delicate texture of the brain.

86. How are the ribs united to the sternum? 87. Describe the spinal column. 88. Give the structure of the vertebra. Where is the spinal cord placed? 89. What is placed between each vertebra? What is its use?

90. Another provision for the protection of the brain, which bears convincing proof of the wisdom and beneficence of the Creator, is the antero-posterior, or forward and backward curve of the spinal column. Were it a straight column, standing perpendicularly, the slightest jar, in walking, would cause it to recoil with a sudden jerk; because, the weight bearing equally, the spine would neither yield to the one side nor the other. But, shaped as it is, we find it yielding in the direction of the curves, and thus the force of the shock is diffused.

Observation. A good idea of the structure of the vertebrÆ may be obtained by examining the spinal column of a domestic animal, as the dog, cat, or pig.

91. The PELVIS is composed of four bones; the two in-nom-i-na´ta, (nameless bones,) the sa´crum, and the coc´cyx.

92. The INNOMINATUM, in the child, consists of three pieces. 38 These, in the adult, become united, and constitute but one bone. In the sides of these bones is a deep socket, or depression, like a cup, called the ac-e-tab´u-lum, in which the round head of the thigh-bone is placed.

90. What is said of the curves of the spinal column? What is represented by fig.10? By fig.11? How can the structure of the vertebrÆ be seen? 91. Of how many bones is the pelvis composed? 92. What is said of the innominatum in the child?

93. The SACRUM, so called because the ancients offered it in sacrifices, is a wedge-shaped bone, that is placed between the innominata, and to which it is bound by ligaments. Upon its upper surface it connects with the lower vertebra. At its inferior, or lower angle, it is united to the coccyx. It is concave upon its anterior, and convex upon its posterior surface.

94. The COCCYX, in infants, consists of several pieces, which, in youth, become united and form one bone. This is the terminal extremity of the spinal column.

In the adult? Describe the acetabulum. 93. Describe the sacrum. Explain fig.12. 94. Describe the coccyx.