Page:Synopsis of the Exinct Batrachia and Reptilia of North America. Part 1..pdf/94

 88 THE EXTINCT BATRACHIA, ItEPTILIA sauna, 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 hugely extended and developed, while the lower extremity of the posterior, or pnncipal 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 hunbar or dorsal vertebrae, 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