FROG: EXTERNAL FEATURES AND BODY-WALL 39 



two components of the bone, but its upper end lies partly 

 in front of the ulna. 1 The upper end of the radio-ulna 

 is hollowed to receive the humerus at the elbow-joint, 

 behind which it projects as the elbow-bone or olecranon 

 process. The wrist consists of six small carpal bones 

 arranged in two rows across the limb. Those of the first 

 row are named according to their position radiale, inter- 

 medium, and ulnare. 2 The second row contains in the 

 early stages of its development five bones, called distal 



§S^ IV 



J1S8 ^ I 



'II 



Fig. 19.- 



-A diagram to illustrate the structure of the limbs and 

 girdles of pentadactyle animals. 



1-5, Distal carpals or tarsals ; 6, radiale or tibiale ; 7, intermedium ; 8, 

 ulnare or fibulare ; 9, centrale ; 10, radius or tibia ; n, ulna or fibula ; 

 12, humerus or femur ; 13, scapula or ilium ; 14, precoracoid or pubis ; 

 15, coracoid or ischium ; i6 } coracoid fontanelle or obturator foramen ; 

 17, glenoid cavity or acetabulum ; 18, clavicle ; 19, metacarpals or 

 metatarsals; 20, phalanges; I.-V., digits. 



carpals, corresponding to five digits, but in the adult frog 

 the third, fourth, and fifth of these have fused. 3 The palm 

 contains five metacarpal bones. The first digit is wanting, 

 but the second and third have each two bones and the 

 fourth and fifth three, according to the number of their 

 joints. These bones are called phalanges. 



1 See p. 434. 



2 For the names of the corresponding bones in the rabbit and man, 

 see p. 435. 



3 In many animals (but not in man) a bone known as the central 

 or centrale lies between the two rows of bones of the wrist. 



