MANUAL OF ZOOLOGY 



SECT. 



complete digits are the second to the fifth of the typical 

 hand. Six carpals only are present. 



The pelvic arch ( Figs. .24 7 and 250) 

 is very peculiarly modified ; it re- 

 sembles in form a bird's " merry- 

 thought," consisting of two long 

 curved bars articulating in front with 

 the transverse processes of the sacral 

 vertebra and uniting posteriorly in 

 an irregular vertical disc of mingled 

 bone and cartilage which bears on 

 each side a deep, hemispherical 

 acetabulum (Fig. 250, G) for the ar- 

 ticulation of the thigh-bone. The 

 curved rods are the ilia (II, P) ; 

 they expand posteriorly and unite 

 with one another in the median plane 

 to form the dorsal portion of the disc 

 and about one-half of the acetabulum. 

 The posterior portions of the disc and the acetabulum are 

 furnished by the ischia (Is), fused with one another in the 

 sagittal plane, and their ventral portions by the similarly 

 united pubcs (Kn). The ilium and ischium are formed of 

 true bone, the pubis of calcified cartilage ; the union of the 

 elements in the median plane is called the symphysis. In 

 the hind-limb the tibia and fibula are fused to form a single 

 tibio-fibula (Fig. 247, TI. FI), and the two bones in the 

 proximal row of the tarsus, namely, the tibiale or astraga- 

 lus (AST) and the fibulare or calcaneum (CAL), are greatly 

 elongated and provide the leg with an additional segment. 

 There are three tarsals in the distal row, one of which ap- 

 pears to represent a central, another the first distal carpal, 

 and the third the fused second and third. There are five 



Fig. 250. — Rana esculenta. 



Pelvic girdle from the right 

 side. G, acetabulum ; II, P, 

 ilium; fs, ischium; Kn, pu- 

 bis. (From Wiedersheim's 

 Comparative Anatomy.) 



