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TEXTBOOK OF ZOOLOGY 



tached anteriorly to the transverse process of the ninth vertebra, and 

 posteriorly it fuses with the pubis and ischium, forming a dishlike 

 concavity, the acetahulum, which receives the hindlimb. The pubis 

 forms the ventral part of the acetabulum, the ischium the posterior, 

 and the ilium the anterodorsal. 



The forelimbs join the body by a ball and socket joint at the 

 glenoid cavity in the pectoral girdle. The large bone which makes 

 this articulation is the humerus. The succeeding bone of the forearm 

 is the radio-ulna, a fusion of two originally distinct bones. The 

 wrist, which follows, contains six carpal bones arranged in two rows. 

 Each hand, or manus, contains four metacarpals following the carpals, 

 and distal to these are four complete digits and an exceedingly small 

 rudimentary fifth near the thumb, the prepollex, consisting of only 



8^? vertebra 



Sacral 



diapophyses 

 cylindrical 



Uium 



Urostyle 



Acetabubm 



- -Ischium 



Fig. 283. — Pelvic girdle of Uie bullfrog, dorsal view. 



a single bone. Each of the four digits, or fingers, extends from a 

 metacarpal bone. This is followed in digits II and III by two 

 phalanges and in digits IV and V by three phalanges. 



The hindlimhs have essentially the same structure as the fore- 

 limbs. The large bone which joins the girdle at the socketlike 

 acetabulum is known as the femur. This bone articulates with the 

 tihiofibula, which, like the bone of the forearm, is a fusion of two 

 bones. The tarsus or ankle differs from the wrist, being composed 

 of two long bones, the tihiale and fibidare, and two small tarsals. 

 There are also two extremely small bones forming the prehallux, or 

 rudimentary sixth toe. Distal to the tarsals are five long meta- 

 tarsals. Each foot contains five complete digits, each following a 

 metatarsal bone. In digits I and II are two phalanges, in digits III 

 and V three phalanges, and in digit IV four phalanges. 



