6 ZOOLOGY. 



(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 dis- 

 tinction 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. 



Abm. Leg. 



I. Shoulder - girdle, consisting I. Hip-girdle, consisting of: 



of: Hip-bone (Ilium) (24). 



Shoulder - blade (Scapula) Pubis. 



(Pig. 2, 17). Rump-bone (Ischium). 

 Collar-bone (Clavicle). 

 Coracoid process (of Sca- 

 pula). 



II. Upper arm : II. Tbigh : 



Upper arm-bone (Humerus) Thigh-bone (Femur) (25). 



III. Fore-arm: III. Leg: 



Eadius (19). Shin-bone (Tibia) (26). 



Ulna (20). Clasp-bone (Fibula) (27). 



IV. Hand: IV. Foot I 



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) Toe-bones (Phalanges) (30). 

 (23). 



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 



