592 REPTILES. 



length of 2 ft., and hopped on its hind-legs like a bird. Iguanodon 

 habitually walked on its hind-limbs, and, like several others, had hollow 

 bones; it reached a. height of 15 ft. Of the carnivorous Dinosaurs, 

 Megalosaurus is a good type. The pelvis has a Crocodilian aspect, 

 for the pubes slope forwards instead of backwards, as in Birds and 

 Iguanodon, etc. The limbs were furnished with powerful claws, and 

 the teeth show much specialisation. SUgosaurus was furnished with 

 heavy armour of plates and spines. Triceratops had three horns on its 

 enormous head. The point of greatest interest about the Dinosaurs 

 is the resemblance to Birds. This was first insisted on by Huxley, and 

 since then it has been generally held that Birds have diverged from a 

 Dinosaur stock. It is, however, fair to notice that by some these 

 resemblances have been declared to be unimportant, while the points of 

 resemblance between Birds and the next order of Reptiles are much 

 dwelt upon. 



Pterosauria. — Flying Reptiles, represented from the lower Jurassic 

 to the Upper Chalk, exhibiting many points of resemblance to Carinate 

 Birds, but still distinctly Reptilian in type. An expansion of the skin 

 seems to have been stretched on the much elongated outermost finger, 

 and to have extended backwards to the hind-legs and the tail. The 

 long bones contained air-sacs as in many Birds. The sternum is keeled, 

 and teeth are often present on both jaws. Some are said to have had 

 an expanse of wing of nearly 25 ft., but others were no larger than 

 sparrows. It is a question how far the resemblances of these forms to 

 Birds are a consequence of similar habits, and how far they can be 

 regarded as indicating true affinities. 



Examples. — Pterodactylus , Rhamphorkytuhus, Pteranodon. 



Relationships of reptiles. — While it is still rash to venture 

 on general conclusions, this much seems clear, that the 

 Reptiles, in their widest sense, form a central assemblage 

 among Vertebrates. As we have noted above, some of the 

 extinct forms exhibit affinities with Amphibians, others with 

 Birds, others again with Mammals. Though we cannot with 

 certainty point to any of the extinct types as directly an- 

 cestral to Birds or Mammals, it seems likely that the ancestors 

 of both were derived from the plastic Reptilian stock. 



