In joints, like the hip, the bones are held together by bands of tough material called ligaments. They are further held together by a covering of connective tissue and by the muscles.

Hygiene of the skeleton. Since the bones of children. are soft and flexible, it is very easy for them to become distorted. Bowlegs, for example, are often the result of allowing children to walk too soon. The bones

have not become sufficiently stiffened to resist the pressure of the weight of the body. Round shoulders often result from a careless position of the body.

Some germ diseases also attack the bones, among them tuberculosis, which sometimes causes a deformity. A common cause of deformity of the bones in small children is lack of the proper kind of nourishment. · Lime salts are necessary for stiffening the bones, and a

A

B

From Blount, Physiology and Hygiene, Row, Peterson & Co.
Fractures; A, a "green stick" fracture of the radius;
B, a fracture of the tibia.

Fig. 175.

lack of these salts in the food results in a disease called the rickets, which causes weak and crooked bones.

In a fracture the bone is broken. To treat a fracture,

the pieces of bone must be brought back into position (this is called "setting" the bone), and must be held there by splints until the ends have become firmly knitted together. It is essential that the bone be kept quiet until the ends have "knitted.".

Sometimes a bone in moving slips out of place. This is a dislocation. Parts of the ligaments are sometimes torn, and the bone may or may not be dislocated. Such an accident is a sprain. This is often very painful, slow to heal, and should be treated with care.

Questions

1. Of what use are the bones?

2. What are the three parts of the skeleton? 3. On your head locate the two parts of the skull. Describe the structure of the vertebral column. 5. How many ribs are there? To what are they attached?

4.

6. Name the bones in the upper limb. In the lower limb.

7. How does the arrangement of the bones in the arm differ from that in the leg?

8. Give the composition of bone.

9. Discuss the growth of bone.

10. Describe a joint.

11. Why should not a heavy strain be put upon the bones of children?

12. What is meant by: rickets, fracture, dislocation, sprain?

CHAPTER XLVI

MUSCULAR SYSTEM

Importance. The muscles of our body constitute about one-half of its weight. By means of these muscles all the movements of the body and of its organs are produced. Not only do they bring about the more obvious motions of the legs and the arms, but also to their action are due the contractions of the heart, of the stomach, and of the other internal organs.

Structure. In this study we will consider only the larger muscles which are attached to the skeleton. Muscles are of various shapes, but they are usually larger in the middle than at either end. They are attached at both ends to bones, usually by a tough, white, inelastic cord, or tendon.

If a complete muscle is examined, it will be found to be covered with a thin sheet of connective tissue. When this is removed, the muscles can readily be divided longitudinally into bundles. These can be split into smaller bundles, which in turn can be divided into a number of long fibers. These fibers have the power to contract and thus to become shorter and thicker. When they shorten, they pull on the bone to which they are fastened and move it.

Their force is always

the result of a contraction, and hence is due always to a pull and never to a push.

Tendons are useful because they permit the thick contracting part of the muscle to be at some distance from the part to be moved. This avoids bulkiness, especially at the joints. The muscles which move the finger, for example, are located in the forearm. Tendons, which can easily be traced on the back of the hand, extend from these muscles to the finger bones. It is evident that this arrangement makes the hand smaller and more graceful and permits of greater ease and delicacy in its movements.

Blood and nerve supply. Muscles are well supplied with blood. Fresh meat is always deep red in color due to the presence of a great quantity of blood. Nerves are also very numerous in muscles; in fact, some muscles are altogether under the control of the nervous system, and are known as voluntary muscles. Most of the muscles fastened to the bones are of this type. Other muscles, such as those in the walls of the stomach, in the walls of the blood vessels, or in the heart are perhaps not completely under nerve control. At any rate, we can not control them and they are called involuntary muscles.

Action of muscles. The action of a muscle can best be understood by a consideration of the arm muscles. The forearm is bent or flexed by the action of a large muscle on the front of the arm, known as the biceps muscle. This is attached by two tendons to the