88 THE EXTINCT BATRACHIA, REPTILIA 



sauria, renders it impossible that they should have reached the ground, in progression, if 

 the posterior were at all extended, and suggests that these reptiles walked erect. That 

 this was the case is demonstrable from the materials at our disposal, I am inclined to 

 believe. 



The ilium, instead of having a vertical position as in reptiles, is longitudinal as in 

 birds. That is, the small process which, in Lacertilians and Crocodiles, projects in advance 

 of the acetabulum, is largely extended and developed, while the lower extremity of the 

 posterior, or principal portion, is raised anteriorly, so that the two together constitute an 

 elongate element, embracing not only the two posterior or original sacral vertebra?, but 

 a considerable number anterior to them. The effect of this is to diminish the proportionate 

 number of lumbar or dorsal vertebra?, to increase the length of the consolidated sacral 

 series, and to throw the acetabulum, and consequently the femur farther anteriorly, and 

 also farther upwards, than in the ordinary reptiles. All these features are characteristic 

 of the birds, and have direct reference to an upright position. Thus it is readily per- 

 ceived that the consolidation of the sacrum, is related to the need of a greater strength of 

 support at a single point; its length, and that of the ilium, to the throwing forwards of 

 that support to beneath the centre of gravity of the animal's body. 



The very elevated position of the acetabulum, and consequently of the usual point of 

 support of the pubes, renders it in the highest degree improbable that the latter bones 

 had the usual direction and position seen in the reptiles. That is, an anterior position 

 would not allow of space for the enlarged visceral cavity which these creatures probably 

 possessed. But it is obvious that in most of the Dinosauria, if not in all, the pubes were 

 not supported in the same manner as in most Reptiles. In Hadrosaurus and Iguanodon 

 there appears to have been absolutely no point of union between ilium and pubis, and in 

 Teratosaurus and Megalosaurus that union, if existing, must have been very slight. The 

 ischia of Stenopelix, Hadrosaurus, and Iguanodon furnish the substitute for this, in an 

 anteriorly directed process for the support of the pubis, a feature otherwise characteristic 

 of the Crocodilia only, among reptiles. 



I conclude, therefore, that the pubes were not directed forwards and that they were 

 not directed backwards either, in those forms at least, where there is no preacetabular sup- 

 port for that bone. They must therefore have been directed downwards, and this is the 

 position they have in the extreme avine form Compsognathus. 



Such ischia as we are acquainted with, are of a remarkably elongate form, simulating 

 those of birds rather those of reptiles, and indicating clearly the existence of a great pelvic 

 visceral cavity. 



From these considerations as to the extent of the pelvic elements we derive further, that 

 the visceral cavity was mainly supported by them and that it was transferred so as to be 



