ORDER DINOSAURIA. 1 1 5 I 



supported by the crescent-shaped first intercentrum. Generally the 

 second intercentrum, like that of Birds, was likewise fused with 

 the centrum of the axis ; but in one Dinosaur (? Megalosaurus) 

 this element exists as a distinct wedge-like bone. 



In the pelvis the pubis and ischium never form the broad and 

 flattened plates found in the Synaptosaurian branch, and they fre- 

 quently assume a more or less rod-like form with expanded ex- 

 tremities (fig. 1073). The ilium {ibid.) frequently presents an 

 expanded form ; and the obturator notch is never converted into 

 a foramen. 



Order VIII. Dinosauria. — The Dinosaurs comprise the largest 

 land Reptiles ; and while some of them approximate closely to the 

 type of structure obtaining in Birds, others come so near to the 

 more generalised Crocodilians that it is almost impossible to give 

 any definition of the order that will separate it from the latter. It 

 is, indeed, probable that in the Lower Trias there lived the common 

 ancestors of the two orders, and the forms from the upper division 

 of the same period indicate not only the close connection between 

 these two groups, but also show some signs of affinity with the 

 Rhynchocephalia. 



It has recently been proposed to divide the Dinosauria into two 

 orders, from the structure of the pelvis, for which the names Or- 

 nithischia and Saurischia have been proposed. If, however, this 

 view be eventually accepted, it would be advisable to adopt the 

 name Ornithopoda for the first division, and to restrict the term 

 Dinosauria to the second, which would include the two groups here 

 termed Theropoda and Sauropoda. In regard to the names of the 

 suborders, it should be mentioned that Professor. Cope first proposed 

 the names Orthopoda and Goniopoda for the groups here termed 

 Ornithopoda and Theropoda, on the ground that the relations of 

 the tibia and fibula were essentially different in the two. According, 

 however, to Professor Huxley, this alleged difference does not exist, 

 and these names are therefore rejected by him. 



This order is entirely extinct, and may be regarded as character- 

 istic of the Mesozoic period ; since it ranges from the Trias to the 

 Uppermost Cretaceous of Maastricht, and the Laramie beds of the 

 United States, and appears to have attained its maximum develop- 

 ment in the Jurassic and Wealden. In space this order was widely 

 distributed over Europe and North America ; and it has also been 

 met with in India and Africa. 



Dinosaurs vary exceedingly in the contour of the body and limbs ; 

 which in some instances were more or less of a crocodilian type, but 

 in others approach very markedly to the avian structure ; the latter 

 feature being most marked in the pelvis and hind limbs. The hind 

 limbs were either moderately or excessively long; while the body 



