306 Elementary Biology. 



the transverse process of the last free vertebra. The ilium 

 is fused posteriorly to the ilium of the other side, and the 

 two ilia together with the representatives of the clavicles and 

 coracoids of the pectoral girdle form a disc, the whole 

 structure being not unlike the 'merrythought' of a fowl. 

 The posterior part of the disc is composed of two fused 

 ischia, the homologues of the coracoids, while the anterior 

 and ventral portion is formed of the two pubes, or the 

 homologues of the clavicles. A union such as this between 

 two bones typically free by means of cartilage is known as a 

 symphysis. As in the pectoral girdle, at the junction of 

 the ilium and ischiurn there is a concavity into which the 

 upper end of the hind-limb fits. Here, however, the pubes 

 take part in the formation of the cavity, which is known as 

 the acetabulum. 



In the typical hind-limb the same arrangement of parts 

 is maintained as in the fore-limb, though the bones are 

 known by different names. The leg is formed by the femur, 

 whose proximal end rotates in the acetabulum and whose 

 distal end articulates with the proximal end of the fore-leg". 

 The fore-leg like the fore-arm is formed of cwo long bones, 

 the fibula externally and the tibia internally. These in 

 turn articulate with a fibulare and a tibiale, between which 

 lies an intermedium. A centrale and five tarsals complete 

 the ankle, or tarsus. To the five tarsals are articulated five 

 metatarsals, which with a number of phalanges form the 

 five digits of the hind-limb. As in the case of the fore- 

 limb, so also the hind-limb of the frog deviates considerably 

 from the typical limb just described. The tibia and fibula 

 are fused together, as were the radius and ulna ; the tibiale 

 and fibulare are long bones and are fused at their extremi- 

 ties, their relatively great size accounting for the extent of the 

 sole of the frog's foot. The other bones of the tarsus are 

 only present in the form of two partly cartilaginous, partly 

 osseous nodules. The five metatarsals and their phalanges 

 are, however, well developed. 



