Each arm can be subdivided into upper arm, forearm, wrist, and hand. The skeleton of the upper arm is a single long bone. The forearm has two bones, one of which is hinged at the elbow to the bone of the upper arm in a way to limit the movement to the single back and forth swing of which the elbow is capable. The other bone of the forearm can be rolled over the one which is fast at the elbow; this is what happens whenever the hand is changed from the palm up to the palm down position. There are eight bones in the wrist; these are irregular in shape, and are so grouped as to permit of a very wide range of movement. The bones of the hand and fingers make up five rows numbering four bones each for the fingers and three for the thumb. The joints are all practically simple hinges except for the one where the thumb joins the wrist, which is a much more flexible joint; flexible enough, in fact, to allow the thumb to be brought opposite any of the fingers. No animal except man enjoys this degree of flexibility in the thumb, so no animal equals man in the nicety of the grasp, particularly of small tools. When we recall how constantly we take advantage of this property of our hands we can realize how greatly our superiority over the lower animals has been aided by this rather slight structural difference between our hands and theirs. [Illustration: THE BONES OF THE ARM _a_, upper arm; _b_, forearm; _c_, wrist; _d_, hand (From Martin’s “Human Body”)] The leg subdivides along the same lines as the arm into upper leg, or thigh, lower leg, or shin, and foot. The order of bones is, on the whole, the same; one in the thigh; two in the lower leg. Instead of a flexible wrist the corresponding bones of the foot are grouped into a less flexible, but much stronger, heel and upper instep. Two of the bones of this group are fused together into one, reducing the total number from eight to seven. The bones of the lower instep and toes correspond in number and arrangement to those of the hand and fingers, but the great toe does not have superior flexibility as does the thumb. There is one bone in the leg, the knee cap or _patella_, that does not correspond to any bone in the arm, although it does correspond to a part of a bone, namely, the projection, at the elbow, of the long bone of the forearm. A feature of the skeleton of the foot that is worth a word is the arching of the instep. This undoubtedly adds greatly to the ease of walking. The natural position for the foot is, of course, with both the heel and the ball of the foot on the ground. For some reason it has become the universal custom among civilized people to raise the heel off the ground by adding a heel to the shoe. This does not seem to make much difference as long as the heel is not too high. In fact soldiers wearing properly fitted heel shoes can march as far and fast as can be expected. Excessively high heels throw the weight too much on the ball of the