The upper and lower limbs are built on the same type, and therefore consist of corresponding parts (cp. Fig. 2). The more similar the functions of the two pairs, the closer their resemblance. In the ox they are much more alike than in man; in the bird, on the contrary, the similarity is much less. A distinction can be drawn in both limbs between the bony girdles (shoulder-girdle and hip-girdle), which serve for union with the trunk-skeleton, and the different subdivisions of the limbs themselves. I place side by side the parts of the arm and leg of man. ARM. │ LEG. I. Shoulder-girdle, consisting │ I. Hip-girdle, consisting of: of: │ Shoulder-blade (Scapula) (Fig.│ Hip-bone (Ilium) (24). 2, 17). │ Collar-bone (Clavicle). │ Pubis. Coracoid process (of Scapula).│ Rump-bone (Ischium). II. Upper arm: │ II. Thigh: Upper arm-bone (Humerus) (18).│ Thigh-bone (Femur) (25). III. Fore arm: │III. Leg: Radius (19). │ Shin-bone (Tibia) (26). Ulna (20). │ Clasp-bone (Fibula) (27). IV. Hand: │ IV. Foot: Two rows of wrist-bones │ Two rows of ankle-bones (Carpal bones) (21). │ (Tarsal bones) (28). Metacarpal bones (22). │ Metatarsal bones (29). Finger-bones (Phalanges) (23).│ Toe-bones (Phalanges) (30). The differences between arm and leg are explained by their different uses. The bones of the leg, used to support the human body, are firmer and thicker, but less movable than those of the arm, which is employed in grasping. Consequently the union between the hip-girdle and the trunk-skeleton is firmer than that of the shoulder-girdle. The radius can rotate upon the ulna, so as to completely turn the hand over; a similar twisting of the foot would not be of use, and cannot be effected. The leg has a knee-pan (patella) (Fig. 31), with which there is no bone in the arm to correspond. In the foot the toes are short, and the remaining parts long; for instance, one of the tarsal bones, the calcaneum (heel-bone), is strongly developed and projects behind (28*). In the hand, the digits are relatively long, and since the tip of the thumb can be made to touch the tips of all the fingers, are admirably adapted for grasping. [Illustration: FIG. 2.—The Human Skeleton. ] The number of fingers or toes is at most five, but may be less. The horse has a single digit to each limb; the ox, two well developed and two remaining as rudiments; the pig, two large and two small; while the dog has four toes in the hind foot, five in the fore foot.