Outlines of Creation

by Elisha Noyce

The bones consist of earthy matter, chiefly phosphate of lime, held together by a sort of cartilage, and arranged in fine scales or plates forming interstices or cells (fig. 76), these are large in the centre of the bone so as to make it nearly (and in some instances quite) hollow, and very small at the surface, so as to make it there nearly solid; this arrangement is found to be the very best to secure strength and lightness, together with a very slight degree of flexibility. The general form of a long bone is that of a shaft, having an enlargement at either extremity, the shaft is generally curved slightly so as to give elasticity, and is more solid than the ends, which are expanded to give size and firmness to the joints, and porous to keep them light; the shaft is small and close in its texture, that there may be plenty of room for the muscles which lie on and cover it. The skeleton then, consists of bony cases which enclose the viscera, a series of levers covered with, and moved by the muscles, and the whole forming a solid framework to support the soft parts. All the various motions of the body, from the winking of the eyelid and the wonderfully adjusted motions of the eye itself—which are so accurate, that a certain perceptible motion is required to look alternately at one side and the other of a pin's head—to the most powerful stroke of the arm, are performed by the contraction of the muscles. But there are several actions which would at first appear to be produced by elongation instead of contraction, such as the protrusion of the tongue, the winking of the eyelids, and the closure of the lips; but the first of these is produced by the contraction of a muscle which is attached at one extremity to the under part of the root of the tongue, and at the other to the inner part of the lower jaw, which, when it contracts, draws the whole tongue forwards, causing a part of it to protrude; the eyelids and lips are closed by circular muscles surrounding them, which, by contraction, draw together those parts.

FIG. 79.—INVOLUNTARY MUSCULAR FIBRE.

FIG. 80.—HEAD OF AN INFANT.

The muscles form the flesh of an animal, or that part which is of a red colour, and which is called lean (in contra-distinction to fat), they are composed of fibres, each fibre made up of a number of fibrils, and the whole bound up together by means of a fine membrane, called areolar tissue. Each of these fibrils consists of a number of cells pressed closely together and having a peculiar bearded appearance (figs. 77, 78). It is by the sudden approximation and flattening of these cells that the muscle is shortened during contraction, but the contraction of each fibril is only for an instant, and then a relaxation and elongation of the cells takes place, which is followed by a second contraction, and so on. Now, the way in which a muscle keeps in a state of permanent contraction is this: the various fibrils or strings of cells relieve each other instead of all contracting and all relaxing together, and in this way a part only of the fibrils are in a state of contraction at any given time, while the others are relaxed, and as one begins to relax another contracts, and so keeps up a state of contraction in the muscle up to a certain point, when the contractions become gradually more feeble, and finally cease altogether; the muscle is then exhausted, but, if allowed to rest awhile, it again obtains its contractile power. This peculiar contractile power is a physical one, and exists for a short time after death, that is, until its perfect structure is altered by the beginning of decomposition; and what is a curious fact, the muscles of a dead body stimulated to contraction by pricking or galvanism, will tire and again obtain their contractility by rest, just as in the living body. The nature of the stimulus which causes the muscles to contract during life is not known; but, whatever it may be, it is conveyed from the spinal cord and brain, through the medium of a set of nerves, called the "motor nerves," or nerves of motion, to the muscles, to every fibre of which they are distributed. There is, however, another set of nerves which have nothing to do with motion, although exactly similar in appearance and generally associated and bound up in the same sheath with them; these are the nerves of sensation. They take their origin from every part possessed of sensibility or feeling—more especially the skin—and convey every impression of feeling to the brain. The muscles are not all under the control of the will, for the muscles of the heart, bowels, &c. are quite out of our control. Those which are subservient to our will are called "voluntary" muscles, or the "muscles of animal life," while those out of the control of the will, are the "involuntary" muscles, or "muscles of organic life" (fig. 79). These last have a structure different to the voluntary muscles, being composed of flattened fibres containing granules and overlapping each other. The tendons are the cord-like extremities of the muscles which connect them to the bones; they are fibrous and slightly elastic, flexible, and exceedingly strong; while moist they have a splendent appearance, somewhat like mother-of-pearl.

The ligaments are the strong fibrous bands which connect the bones together. Cartilages are substances of a white colour, smooth in their texture, and not very flexible; they are connected to the bones which they sometimes serve to prolong, and are themselves often converted into bone in old people, by the deposition of earthy matter within their structure, in fact, they may be considered as bone in an undeveloped state; for, in the infant, many parts are cartilaginous, which, in the adult, are bony; such as the ends of the long bones, the bones of the nose, &c.

FIG. 81.—HEAD OF AN ADULT.

With respect to the development of the form of the human body, there are two chief conditions which influence it, namely, age and sex. With respect to age, the proportional magnitudes of the different parts, early and late in life, vary very considerably. In the infant (fig. 80) the hand is by far the most completely developed (in size), next to this the abdomen, then the chest and upper extremities, and, finally, the lower extremities. In the adult (fig. 81), the largest measurement is round the chest and shoulders, but in the infant it is round the head; in the adult the lower extremities weigh one half of the whole body, but in the infant not one quarter. The infantile face has many peculiarities, so also has the face of old age (fig. 82). In the infant the lower part of the face is but little developed, the lower jaw is small, the chin scarcely at all prominent, and the distance from the nose to the chin very short, owing to the absence of the teeth, or (when formed) their smallness. The bones of the nose are scarcely formed, and this organ has therefore no bridge, properly so called; the nostrils are small, the lower part of the forehead small, smooth, and rounded, and the arches of the eyebrows but little prominent. The cheek-bones are small, and so are the bony arches which join them to the temples; the cheeks are full of fat, and the angles of the jaws rounded. In middle age the lower part of the forehead becomes more fully developed, the bony edges which support the eyebrows project and overhang the eyes, the bridge of the nose and the nostrils become more fully formed, the space from the nose to the chin is greater, the teeth cause the lips to be pushed more forward, the lower jaw is larger, and the cheek-bones show more plainly. In old age the whole upper part of the face becomes more marked, the nose and eyebrows still more prominent, the cheeks hollow from absorption of the fat, the space from the nose to the chin (as in infancy) shortens from loss of teeth, but the chin, being more fully formed, projects as the jaw rises to fill the space occupied by the teeth. The angles of the jaw are also very sharp and square, the eyes sunk in the head, and the whole skin of the face loosened and wrinkled from loss of substance beneath. With respect to sex, in the Male the facial bones are more fully formed, the shoulders broader and higher, the collar-bones longer and more curved, the chest wider, the hips narrower, and the legs longer, and every bone has its processes or markings more fully developed, and is more contorted from the action of the muscles, which are larger and more powerful than in the Female. In the Female (fig. 83) there is a greater deposition of fat, and, in many other respects, a tendency to a child-like conformation.