in 



HIND-LIMB 



51 



is the ischium (Is) ; like the ilium it is made of true bone. 

 The third, or pubis (Kn), 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 either 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 ; 

 Fig. 13, C), harving a gently curved 

 shaft and extremities of calcified 

 cartilage. Its rounded proximal 

 extremity, or head, fits into the 

 acetabulum : its distal end articu- 

 lates with the single bone of the 

 shank, the tibio-fibula (TI. FI). 

 This, the longest bone in the body, 

 also has a shaft and extremities, 

 and is further distinguished 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 calcaneum) 

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

 additional segment to the limb, thus increasing the 



E 2 



FIG. 14. The hip-girdle of 

 a Frog seen from the 

 right side, (x 2.) 

 G. acetabulum ; Kn. 

 pubis ; //., P. ilium ; 

 Is. ischium. (From 

 Wiedersheim's Com- 

 parative Anatomy.) 



