242 



THE BIOLOGY OF THE FROG 



IZ- 



distal end of the radio-ulna is widened, and ends in two 

 epiphyses, one for each of the component bones. 



The carpus, or wrist of the frog, contains six bones arranged 

 in two rows. In the proximal row the ulnare and radiate 

 are situated at the ends of the ulna and radius, respectively, 

 and at the inner or preaxial side of the radiale is the centrale. 

 In the distal row the first carpal 

 occurs just behind the rudimentary 

 thumb ; the second carpal, a very 

 small bone, lies behind the second 

 digit ; the outer carpal is of rela- 

 tively large size, and is formed by the 

 fusion of three originally distinct 

 bones one for each of the three 

 outer digits of the hand. Beyond 

 the wrist are the five metacarpals, 

 which form the skeleton of the proxi- 

 mal part of the hand. The first meta- 

 carpal is rudimentary and usually car- 

 tilaginous in the female, but in the 

 male it is larger, and becomes calci- 

 fied or even ossified. The other 

 metacarpals are elongated cylindrical 

 bones, somewhat expanded at the two 

 ends ; the inner one of the four is stouter in the male than 

 in the female, and bears a prominent crest on the inner 

 margin. The metacarpals, except the first, are succeeded 

 by the phalanges, of which each of the two outer digits have 

 three, while the two inner ones have but two. 



The Pelvic Girdle. — The pelvic girdle which supports 

 the hind limbs is a V-shaped mass of bone, the apex of 

 which lies at the posterior end of the skeleton, and receives 

 the tip of the urostyle ; the two anterior ends are united to 



Fig. 69. — Pelvic girdle 

 of the frog from the 

 right side. G, acetab- 

 ulum ; //, ilium ; Is, 

 ischium ; P, pubis. 

 (After Parker and 

 Parker.) 



