HIND-LIMB 



51 



is ventral, and is formed of calcified cartilage. Originally each 

 of these elements is paired, i.e., there is an ilium, an ischium, 

 and a pubis on each side, the three together forming the 

 innominate, but in the adult the right and left ischia and 

 pubes become united in the median 

 plane, the ilia only remaining free. 



The Hind-limb.— The thigh, like 

 the upper arm, is supported by a 

 single long bone, the femur (Fig. 8, 

 FE), having a gently curved shaft 

 and extremities of calcified cartilage. 

 Its rounded proximal extremity, or 

 head, fits into the acetabulum : its 

 distal end articulates with the single 

 bone of the shank, the tibio-fibiila 

 (TI. FI). This, the longest bone 

 in the body, also has a shaft and 

 extremities, and is further distin- 

 guished by grooves running from 

 each end towards the middle of the 

 shaft. Sections show that the grooved portions of the bone 

 contain a double marrow-cavity (Fig. 13, D), and in the young 

 animal there are found two shank-bones which afterwards 

 unite, the tibia on the inner side, the fibula on the outer side. 



The foot, like the hand, is divisible into three regions : 

 the tarsus or ankle, the metatarsus or mid-foot, and the 

 phalanges or toe-bones. The tarsus, like the carpus, 

 consists of two rows, but with only two bones in each. 

 Those of the proximal row {astragalus and calcaneujn) are 

 greatly elongated (AST., CAL,), and furnish an additional 

 segment to the limb, thus increasing the frog's leaping 

 powers : those of the distal row are very small. 



The metatarsals are five in number : those of the first 



E 2 



J^ 



Fig. 14. — The pelvic girdle of 

 the Frog seen from the 

 right side. 

 G. acetabulum ; A'«. pubis ; 

 II. P. ilium ; Is. ischium. 

 (From Wiedersheim.) 



