52 THE SKELETON OF THE FROG 



d. The hand has four complete digits and a rudimentary 

 pollex or thumb. Each digit consists of a proximal 

 metacarpal bone, beyond which are a variable number 

 of phalanges. 



i. The pollex, the anterior or preaxial digit, consists 



simply of a small metacarpal bone, 

 ii. The first complete digit, corresponding to the fore- 

 finger of man, consists of a metacarpal and two 

 phalanges. 



iii. The second digit, corresponding to the middle 

 finger of man, consists of a metacarpal and two 

 phalanges. 



iv. The third, corresponding to the ring-finger of man, 

 consists of a metacarpal and three phalanges. 



v. The postaxial digit, corresponding to the little finger 

 of man, consists of a metacarpal and three 

 phalanges. 



3. The Pelvic Girdle. 



This consists primitively, like the pectoral girdle, of a couple 

 of half-rings of cartilage, fused together below and attached 

 above to the tips of the transverse processes of the sacrum. In 

 the adult frog the girdle is placed very obliquely, so as to be 

 nearly parallel with the vertebral column instead of at right 

 angles to it. 



Each half presents on its outer aspect a cup-shaped cavity 

 the acetabulum forming, with the thigh bone, the hip-joint : we 

 accordingly distinguish an iliac portion above the acetabulum 

 and an ischio-pubic portion below it, corresponding respectively 

 to the scapular and coracoid divisions of the pectoial girdle. 



i. The ilium forms the anterior and upper half of 

 the acetabulum, and extends forwards as an 

 elongated laterally compressed bar, which is 

 attached in front to the transverse process of the 

 sacrum and bears along its dorsal surface a 

 prominent vertical ridge of bone, the iliac crest, 

 ending behind in an abrupt vertical border. 

 Posteriorly the two ilia meet each other and are 

 united together in the median plane to form the 

 iliac symphysis. 



