The Muscles.—The muscles form the lean meat in any animal. They make up about one half the weight of the body. Each muscle is a bundle of thousands of little threads held together by other finer threads, while the whole is surrounded by a thin sheet. Little bundles formed of several of these threads called fibers may be seen in a piece of cooked beef picked to pieces. There are over five hundred muscles in the body.
Fig. 83 —Fifty of the muscles just under the skin. Note the white cords, the tendons in the regions of the hands and feet.
Fig. 84 —The biceps muscle contracted above and relaxed or loosened below.
Some of the muscles are more than a foot long and have the shape of a ribbon. Some are circular like those around the mouth, eyes, and stomach, while others are large in the middle and taper toward the ends.
How the Muscles are fastened to the Bones.—The two ends of a muscle are attached to different bones. In many cases the muscle is not joined directly to the bone, but is connected to a tough white cord called a tendon. The tendon is then fixed to the bone.
Several of the muscles in the forearm run into tendons in the wrist because if the muscle part were to extend along the wrist, this part of the arm would be large and clumsy instead of graceful and slender. Some of these tendons may be seen to move by bending the wrist and then working the fingers.