A Treatise on Anatomy, Physiology, and Hygiene Part 4

_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 part.i.tion 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 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-oste-um_; that which covers the cartilages is called _per-i-chondri-um_. When this membrane invests the skull, it is called _per-i-crani-um_.

[Ill.u.s.tration: Fig. 6. A section of the knee-joint. The lower part of the femur, (thigh-bone,) and upper part of the tibia, (leg-bone,) are seen ossified at 1, 1. The cartilaginous extremities of the two bones are seen at _d_, _d_. The points of ossification of the extremities, are seen at 2, 2. The patella, or knee-pan, is seen at _c_. 3, A point, or centre of ossification.]

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 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_.

[3] Some anatomists reckon more than this number, others less, for the reason that, at different periods of life, the number of pieces of which one bone is formed, varies. _Example._ The breast-bone, in infancy, has _eight_ pieces; in youth, _three_; in old age, but _one_.

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 _vitre-ous_, or gla.s.sy 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 pa.s.sages 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 _sutures_. 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.

[Ill.u.s.tration: Fig. 7. 1, 1, The coronal suture at the front and upper part of the skull, or cranium. 2, The sagittal suture on the top of the skull. 3, 3, The lambdoidal suture at the back part of the cranium.]

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.

[Ill.u.s.tration: Fig. 8. 1, The frontal, or bone of the forehead. 2. The parietal bone. 3, The temporal bone. 4, The zygomatic process of the temporal bone. 5, The malar (cheek) bone. 6, The superior maxillary bone, (upper jaw.) 7, The vomer, that separates the cavities of the nose. 8, The inferior maxillary bone, (lower jaw.) 9. The cavity for the eye.]

82. The TRUNK has fifty-four bones--twenty-four _Ribs_; twenty-four bones in the _Spinal Column_, (back-bone;) four in the _Pelvis_; the _Sternum_, (breast-bone;) and the _Os hy-oides_, (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 _Thorax_ (chest) and _Ab-domen_.

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 fas.h.i.+on, in many instances, has nearly inverted this order. This cavity contains the lungs, heart, and large blood-vessels.

[Ill.u.s.tration: Fig. 9. 1, The first bone of the sternum, (breast-bone.) 2. The second bone of the sternum. 3, The cartilage of the sternum. 4, The first dorsal vertebra, (a bone of the spinal column.) 5, The last dorsal vertebra. 6, The first rib. 7, Its head. 8, Its neck. 9, Its tubercle. 10, The seventh, or last true rib. 11, The cartilage of the third rib. 12, The floating ribs.]

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 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 _verte-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 ca.n.a.l, is formed immediately behind the bodies of the vertebr, in which is placed the _me-dulla spi-nalis_, (spinal cord,) sometimes called the pith of the back-bone.

89. Between these joints, or vertebr, is a peculiar and highly elastic substance, which much facilitates the bending movements of the back. This compressible cus.h.i.+on of cartilage also serves the important purpose of diffusing and diminis.h.i.+ng the shock in walking, running, or leaping, and tends to protect the delicate texture of the brain.