bone knit together far more readily than do the torn ends of a tendon.

After all, however, the ligaments and bone surfaces are quite as important to us as the tendon, because they determine the direction in which a bone must move. Some of them allow movement in one direction, some in another. Prove this for

Muscle
fiber

-Tendon

Bone

tube

Bone covering

yourself. By every twist that you can make, try to decide where your joints are and what style of joint each one is. You will find that some work back and forth like a hinge, while others have the

power to move back and forth and sidewise too. The different kinds of movement are the result of different kinds

MUSCLE ENDING IN TENDON; TENDON of joints. Each is needed in

FASTENED TO BONE

(After Schmidt)

its particular place.
Begin with the hinge joint

where your skull is joined to the upper end bone of the spine. This allows you to bend your head up and down, and nothing more. But just below, between the next two bones, is a joint of another sort. This allows you to turn your head from side to side. Thanks to the two joints acting as one, you can move your head in every direction.

Whirl your arm round and round and know that you are using the most movable joint in the entire body. It is a so-called ball-and-socket joint. The hip is supplied with another of the same kind.

When we think of the work which the hip and the knee have to do for us, and of the strain we are ready to put on them at any moment, we understand why the hip and knee joints should be among

BONES AND JOINTS

OF THE LEG

the firmest and the strongest points of the whole body. The knee itself is a wonderful structure. And here we have an admirable chance to study ligaments. They are firm and white and tough, being in all this quite like

tendons. Moreover, when once torn they are as slow to heal as is a tendon. Ligaments do the work of holding bones to each other, whereas tendons hold muscles to bones.

The great hinge joint of the knee is supplied with ligaments which allow it to bend one way, but which absolutely forbid any bending in an opposite direction. If it were not for the stout ligaments which

hold the bones

together in a definite relation, our knees would bend backwards and forwards with equal ease, and walking would be forever out of the question. Elbow as well as knee, fingers as well as toes, all act on the plan of the hinge.

Two kinds of joints are thus seen to be most prominent in the body of man: (1) ball and socket; (2) hinge.

CUT THROUGH THE
HINGE JOINT OF THE
ELBOW

This completes the outline of the bony and muscular machinery of our bodies. We have seen that the ends of our bones are shaped to meet each other, that they

KNEE JOINT WHEN STRAIGHT

Notice the position of the knee pan

(After Schmidt)

KNEE JOINT BENT FAR OVER

Notice the ligaments that hold the bones together

(After Schmidt)

are carefully fitted together, that tough ligaments hold the one to the other, and that muscles end in tendons which draw the bones in such directions as the joints allow.

CHAPTER VIII

THINGS THAT HINDER STRENGTH AND SPEED

Various public schools were in a state of high excite、 ment during the spring of 1905. The following item in the New York Times shows the reason for it:

Schoolboy athletes are to hold their contests on the roofs of the available public school buildings in the boroughs of Manhattan and Brooklyn. . . . Each school is to enter five boys in each individual event, and two teams in each relay race. Medals will be given to first, second, and third in each event, and a trophy will be presented to the school scoring the most points.

Boys under thirteen, in these events, competed in the potato race, the standing broad jump, and the relay race for teams of four boys, each running twice across the roof. Boys under fifteen had the same potato race, with running high jump instead of broad jump; and in the relay race of four boys, each ran four times instead of twice across the roof. Boys over fifteen did other things in addition.

Throughout the spring of that year, wherever New York boys could find a roof large enough or a space of ground unoccupied, there they went for fun, for exercise, and for trophies. But the doctors of the city, the fathers, the mothers, and the teachers believed most in the exercise.