192 



ANATOMY OF VERTEBRATES. 



122 



homology of their homotypes in the fore-foot, fig. J 10. The first 

 metatarsal supports two phalanges, fig. 123, i ; the second, three ; 

 the third and fourthj each four phalanges ; and the fifth, three. The 



first and second toes are opposed 

 to the other three in the hind foot, 

 contrariwise to the arrangement in 

 the fore foot. 



In the Pterodactyle a fig. Ill, 

 the hind limb adhered closely to 

 the lacertian type ; the metatarsals 

 were distinct; the phalanges in- 

 creased in number from the first 

 to the fourth toe, but retained 

 more equality of length than in 

 lizards : all the five toes were 

 unguiculate, the claw phalanx com- 

 pressed and deep. Although in 

 some species there were four or 

 five sacral vertebra?, the hind- 

 limbs were too feeble to sustain 

 the body, as in Birds : they more 

 probably served to suspend it, as 

 in Bats, with a concomitant 

 strengthening of the claws. 



The reptilian hind-limbs, with 

 their arch, acquired the most com- 

 plex structure in the great extinct 

 Dicynodont l and Dinosaurian 2 

 orders. In Dicynodon tigriceps 

 ossification extended over the 

 whole of the interspace between 

 the ischium and pubis, obliterat- 



m 



ing altogether the obturatorial 



Bones of leg and foot, Monitor 



foramina: and both iliac and 

 ischial bones articulated, as in 

 edentate mammals with a long 

 sacrum. In the Iguanodon six 

 vertebras were modified with interlocking centrums and neural 



C3 



arches, the latter resting on, and suturally joined to, the 

 contiguous halves of two centrums. The femur exhibited an 

 upper and external ( great trochaiiter,' besides the inner tro- 



1 CJLV. 



CXLVI. (1841), pp. 114, 130. 



