Of the bones that make up the eye sockets not much need be said, except that they have a great deal to do with determining the shape of the upper part of the face and so the appearance. There are bones within the nostrils that are very irregular in outline. Their effect is to increase greatly the surface over which the air that is breathed must pass, enabling it to become both warm and moist before entering the lungs. The jaw bones serve as receptacles for the teeth; the lower jaw, which is the only movable bone of the head, except for the tiny bones within the ears, has also the duty of operating as a mill in reducing the food to suitable form for swallowing. To aid in this function the lower jaw is hinged to the rest of the skull in such a way that it not only opens and closes but can slide forward and back or from side to side. All these motions are used in chewing. There are twenty-two bones altogether in the skull, not counting the three tiny ones in each ear which will be described later. [Illustration: FRONT VIEW OF TRUNK AND LIMB ARCHES _c_, collar bone; _s_, shoulder blade; _Oc_, innominate bone (From Martin’s “Human Body”)] [Illustration: SIDE VIEW OF THE SPINAL COLUMN _C_ 1-7, cervical; _D_ 1-12, dorsal; _L_ 1-5, lumbar; _S_ 1, sacrum; _Co_ 1-4, coccygeal. (From Martin’s “Human Body”)] The body consists of trunk and limbs, and each part has its skeleton. The skeleton of the trunk consists of the spinal column, the rib cage, the shoulder girdle, and the hip girdle. The skeletons [Illustration: Photo, A. N. Mirzaoff A FRENCH METHOD OF MEASURING VERTICAL CONFORMATION, CONSIDERED IMPORTANT FOR ATHLETES] [Illustration: Photo, A. N. Mirzaoff THE CURVE OF THE SPINE MEASURED AND DRAWN FOR STUDY OF AN ATHLETE’S POSSIBILITIES] of the limbs are all according to a single plan to be described in a moment. The spinal column is a remarkable example of strength combined with flexibility and elasticity. It is made up of thirty-three bones or _vertebræ_; each of these has a disk-shaped part known as the _body_, and these disks are placed in line as shown in the figure. Between each disk and its neighbor is an elastic pad composed of a mixture of cartilage and elastic connective tissue. There is a small amount of give in each pad and this, taken along the whole length of the spinal column, is enough to give it the great flexibility which it enjoys. During the day the weight of the body packs these pads down hard, so that it is said that a man may be as much as an inch shorter at night than in the morning. Behind the disk each vertebra has an arch of bone, and beyond and beside this arch most of them have projections. All the arches together make up a bony canal which contains and protects the spinal cord. The projections serve for the attachment of the ribs and the back muscles by which the bending motions of the body are made.