The Skeleton : Head, Trunk, Limbs

Hygienic Physiology: with Special Reference to the Use of Alcoholic Drinks and Narcotics
by Joel Dorman Steele, Ph.D.

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Classification of the Bones

For convenience, the bones of the skeleton are considered in three divisions: the head, the trunk, and the limbs.

1. The Head.

The Bones of The Skull And The Face form a cavity for the protection of the brain and the four organs of sense, viz.: sight, smell, taste, and hearing. All these bones are immovable except the lower jaw, which is hinged at the back so as to allow for the opening and shutting of the mouth.

The Skull is composed, in general, of two compact plates, with a spongy layer between. These are in several pieces, the outer ones being joined by notched edges, sutures, in the way carpenters term dovetailing.

The peculiar structure and form of the skull afford a perfect shelter for the brain - an organ so delicate that, if unprotected, an ordinary blow would destroy it. Its oval or egg shape adapts it to resist pressure. The smaller and stronger end is in front, where the danger is greatest. Projections before and behind shield the less protected parts. The hard plates are not easy to penetrate. The separate pieces with their curious joining disperse any jar which one may receive, and also prevent fractures from spreading.

The frequent openings in this strong bone box afford safe avenues for the passage of numerous nerves and vessels which communicate between the brain and the rest of the body.

2 The Trunk.

The Trunk has two important cavities. The upper part, or chest, contains the heart and the lungs, and the lower part, or abdomen, holds the stomach, liver, kidneys, and other organs. The principal bones are those of the spine, the ribs, and the hips.

The Spine consists of twenty-four bones, between which are placed pads of cartilage. A canal is hollowed out of the column for the safe passage of the spinal cord. at the back and on either side are abundant for the attachment of the muscles. The packing acts as a cushion to prevent any jar from reaching the brain when we jump or run, while the double curve of the spine also tends to disperse the force of a fall. Therefore on every side the utmost caution is taken to guard that precious gem in its casket.

The Perfection of The Spine surpasses all human contrivances. Its various uses seem a bundle of contradictions. A chain of twenty-four bones is made so stiff that it will bear a heavy burden, and so flexible that it will bend like rubber; yet, all the while, it transmits no shock, and even hides a delicate nerve within that would thrill with the slightest touch. Resting upon it, the brain is borne without a tremor; and, clinging to it, the vital organs are carried without fear of harm.

The Skull Articulates with (is jointed to) the spine in a peculiar manner. On the top of the upper vertebra are two little hollows, nicely packed and lined with the synovial membrane, into which fit the corresponding projections on the lower part of the skull, an. Therefore the head can rock to and fro. The second vertebra (axis) has a peg, e, which projects through a hole, c, in the first.

The surfaces of both vertebra are so smooth that they easily glide on each other, and therefore, when we move the head side wise, the atlas turns around the peg, e, of the axis.

The Ribs, also twenty-four in number, are arranged in pairs on each side of the chest. At the back, they are all attached to the spine. In front, the upper seven pairs are tied by cartilages to the breastbone (sternum); three are fastened to each other and to the cartilage above, and two, the floating ribs, are loose.

The natural form of the chest is that of a cone diminishing upward. But, owing to the tightness of the clothing commonly worn, the reverse is often the case. The long, slender ribs give lightness, the arched form confers strength, and the cartilages impart elasticity, - properties essential to the protection of the delicate organs within, and to freedom of motion in respiration.

The Hip Bones, called by anatomists the innominata, or nameless bones, form an irregular basin styled the pelvis. In the upper part, is the foot of the spinal column - a wedge-shaped bone termed the sacrum (sacred), firmly planted here between the wide spreading and solid bones of the pelvis, like the keystone to an arch, and giving a steady support to the heavy burden above.

3. The Limbs.

Two Sets of Limbs branch from the trunk, viz.: the upper, and the lower. They closely resemble each other. The arm corresponds to the thigh; the forearm, to the leg; the wrist, to the ankle; the fingers, to the toes. The fingers and the toes are so much alike that they receive the same name, digits, while the several bones of both have also the common appellation, phalanges. The differences which exist grow out of their varying uses. The foot is characterized by strength; the hand, by mobility.