Principles of Public Health / A Simple Text Book on Hygiene, Presenting the Principles Fundamental to the Conservation of Individual and Community Health

by Thomas Dyer Tuttle

Fig. 79. The muscles.

MUSCLES AND TENDONS

What muscle is

The lean meat of any animal is composed entirely of muscle tissue. It is the function of the muscles to move the body.

Fig. 80. The biceps muscle contracted.

How the muscles work

The muscles are nearly all attached to the bones. They are just long enough to let the joint straighten out when the muscles are at rest, but when the joint bends the muscle contracts. When a muscle contracts it becomes shorter and thicker. Sometimes it becomes very much thicker in one place. Every boy knows how much thicker the arm muscle (biceps) becomes when he bends his elbow hard. He calls this "showing his muscle."