THE MUSCLES THAT part of the animal's body which we call lean meat is composed of muscles. We have already explained that muscles are composed of threads, etc., put together in great numbers, forming bundles. So numerous are these threads and bundles in some cases, that the muscles which are composed of them have a strength truly wonderful.
Toward the end of the muscle, the fibers cease, and the structure is so modified as to become a white cord of great density and strength. This cordy substance is fastened to the bone so strongly, that it is impossible, except in some rare cases, to detach it. Generally the bone will sooner break than this attachment will give way. Sometimes this cord spreads out like a membrane. It is then called fascia or aponeurosis.
The fibres of a muscle have the peculiar property of contracting under a nervous stimulus sent to them by the will. These contractions cause them to act as pulleys, and to move the bones, and consequently the limbs and body, in such direction as the will commands. This is the special use of the muscles. All our movements are caused by them. They pull us about, not blindly and at a random, but under the direction of an intelligent will.
The manner in which a muscle acts, with the cord attached, may be seen by examining the leg or 11 drumstick " of a fowl. If the cord on one side be pulled, the claws are shut; if that upon the other side be drawn, they will open. If both be pulled, they are held fast in one position, neither opening nor shutting.
An examination of a piece of boiled lean meat will show the threads of which it is composed. With proper instruments, these may be unraveled, as it were, until fibers will be found not larger than a spider's web. These, covered with sheaths of great delicacy, extend beyond the fleshy fiber, and with the condensed connecting the fibers, are condensed into tendon.
Millions of these sheathed fibers are gathered into a bundle, and covered with a sheath, and thus form what is called afasciculus. A muscle is a number of these fascicula made into a bundle, and covered with a sheath called afascia (Fig. 1).
The arm is a number of muscles bundled together, and covered, likewise, by a fascia.
The fibers in a fasciculus being parallel, act together. But the fasciculous bundles which make up a muscle act in various ways. SHAPE OF THE MUSCLES: Some muscles are fusiform or spindle shaped, so that the attachment occupies but a small space (Fig. 20).
Other muscles are radiate or fanshaped (Fig,21). Such is the temporal muscle, the thin edge of which is attached to the side of the bead, without producing an elevation or deformity.
In some cases the faseiculi are arranged upon one or both sides of a tendon. In this way a great number may concentrate their action upon a single point. Such muscles are called penniform, being shaped like a feather (Fig. 22). In other instances, the fascieue form circular muscles, orbiculares, or sphincters, as
they are called. These surround certain openings into the body, which they are designed to close, either in whole or in part. They surround the eyelids, the anus, the mouth of the womb, etc. (Fig. 23).
In still other instances the fasciouli are ranged side by side in rings, forming muscular tubes. By the successive contraction of these rings, any substance is driven
through the tube, as food or drink through the gullet of a cow. Fig. 24 is a section of the gullet: a, b, show the circular fibers; c, the longitudinal.
Sometimes the fasciculi curve around in parallel layers or interlace with each other, forming a bag or pouch. By the contraction of these fasciculi, the contents of the bag will be turned from side to side as in the case of the stomach, or driven out, as in that of the heart. Fig. 25 shows the muscles of the stomach: L, represents the fibers running in one direction; c, in another; E, lower end of gullet; 0, pylorus, D, beginning of duodenum, or second stomach.
NUMBER OF MUSCLES. The muscles of the body are as numerous as the ropes of a ship, there being five hundred or more. Some anatomists reckon more, some less.
They are divided into those of the head and neck, those of the trunk, those of the upper extremities, and those of the lower extremities.
They are too numerous to be named and individually described in this brief account of them. A part of them are voluntary, that is,
under the control of the will; while another part are involuntary, moving without reference to the will. The heart is of the latter kind, it being necessary for it to keep moving when the will and mind are asleep.
On the back there are six layers of muscles, one above another. Such a number are necessary to perform the numerous movements of the back, neck, arms, etc. Every expression of the human face, as joy, sorrow, love, hate, hope, fear, etc., is produced by the gentle pulling of muscles, made expressly to indicate these emotions.
The diaphragm is a large flat muscle, reaching across the great cavity of the body, and dividing the chest from the abdomen. It is penetrated by the gullet going to the stomach, and by the great bloodvessels leading to and from the heart. It is shaped like the cover of a dinnerdish, the convex surface being turned up. When the breath is drawn in, it sinks clown towards a level thus enlarging the chest at the expense of the belly. When the breath is thrown out, the reverse takes place. MODE OF ACTION. The contractibility of a muscle, of which I have spoken, is simply its power of shortening itself. The hand is raised by the shortening of a muscle in front, attached to the bone above the elbow, and to a bone below the elbow. The contraction of an antagonistic muscle behind, also attached above and below the elbow, brings the hand back to its place. Fig. 26 shows how all joints are moved: 1, is the bone of the arm above the elbow; 2, one of the bones below the elbow; 3, the muscle which bends the elbow; 4, 5, attachments of muscles to bones; 6, the muscle that extends the elbow; 7, attachment to elbow; 8, weight in hand. The muscle, 8, contracts at the central part, and brings the hand up to 9, 10.
The complication, variety, and
swiftness of motion, executed by muscles, are past conception. Every
movement which a human being makes, from the heavier motions of the
farmer in cultivating his fields, up to the magic touches of the
painter's brush, and the methodical frenzy with which the great master's
fingers sweep the piano, are all made by muscles obeying an intelligent
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