By the preceding engraving, it will be seen, that the cranium, or skull, consists of several distinct pieces, which are united by sutures, (or seams,) as represented by the zigzag lines; a, being the frontal bone; b, the parietal bone; c, the temporal bone; and d, the place of the occipital bone, which forms the back part of the head, and therefore is not seen in the engraving. The nasal bones, or bones of the nose, are shown at e; f, is the cheek bone; g, the upper, and h, the lower, jaw bones; i, i, the spinal column, or back bone, consisting of numerous small bones, called vertebræ; j, j, the seven true ribs, which are fastened to the spine, behind, and by the cartilages, k, k, to the sternum, or breast bone, l, in front; m, m, are the first three false ribs, which are so called, because they are not united directly to the breast bone, but by cartilages to the seventh true rib; n, n, are the lower two false, which are also called floating, ribs, because they are not connected with the breast bone, nor the other ribs, in front; o, o, p, q, are the bones of the pelvis, which is the foundation on which the spine rests; r, r, are the collar bones; s, s, the shoulder blades; t, t, the bones of the upper arm; u, u, the elbow joints, where the bones of the upper arm and fore arm are united in such a way that they can move like a hinge; v w, v w, are the bones of the fore arm; x, x, those of the wrists; y, y, those of the fingers; z, z, are the round heads of the thigh bones, where they are inserted into the sockets of the bones of the pelvis, giving motion in every direction, and forming the hip joint; a b, a b, are the thigh bones; c, c, the knee joints; d e, d e, the leg bones; f, f, the ankle joints; g, g, the bones of the foot.
The bones are composed of two substances,—one animal, and the other mineral. The animal part is a very fine network, called the cellular membrane. In this, are deposited the harder mineral substances, which are composed principally of carbonate and phosphate of lime. In very early life, the bones consist chiefly of the animal part, and are then soft and pliant. As the child advances in age, the bones grow harder, by the gradual deposition of the phosphate of lime, which is supplied by the food, and carried to the bones by the blood. In old age, the hardest material preponderates; making the bones more brittle than in earlier life.
As we shall soon have occasion to refer, particularly, to the spinal, or vertebral column, and the derangement to which it is liable, we give, on page [72], representations of the different classes of vertebræ; viz. the cervical, (from the Latin, cervix, the neck,) the dorsal, (from dorsum, the back,) and lumbar, (from lumbus, the loins.)
Fig. [2], represents one of the cervical vertebræ. Seven of these, placed one above another, constitute that part of the spine which is in the neck.
