Page:Synopsis of the Exinct Batrachia and Reptilia of North America. Part 1..pdf/100

 94 THE EXTINCT BATRACHIA, REPTILIA the most contracted. The wide caudals continue without contraction to the point where the tail reaches the ground. They then begin to elongate. The anterior vertebrae thus form a massive column, which no doubt supported the weight of these monsters. That the ischia performed this function in part in LEelaps, is evident not only from their more massive structure, but from the more elongate caudal vertebrae, while the still more slender caudals in the known Triassic genera, adds to the evidence derived from the ischia as to their use. In the ilium of Hadrosaurus the slender hooked process and the expanded tuberosity both exist, and I am disposed to place the former posteriorly, and the latter anteriorly and externally as the most probably correct relation. This, moreover, throws posterior to the acetabulum, the more elongate articular face, where one might look for the ischiadic suture with propriety. This arrangement, however, presents the apparent anomaly of position, that the planes of the inner faces of the ilia are made to converge instead of di-verge, thus rendering the interiliac cavity remarkably narrow. There can, however, be no doubt that this is really their position in Iguanodon, judging from Owen's figures (above), III. and iv., and that the sacral diapophyses really rest on the convergent faces of the ilia, whose planes are directed inwaids as well as downwards. This acids still fur-ther to the peculiar ensemble of characters of these Dinosauria. This relation has already been described as the true one, by Leidy. The anterior prolongation of the ilium in Hadrosaurus appears to be less slender and more plate-like than in Iguanodon and Scelidosaurus, where it is remarkably produced. Nevertheless, in the accompanying cut, the restoration (by Dr. Horn) of the anterior por-tion may be too much dilated, and is probably not long enough. Pais. This element of Hadrosaurus has never been described. I believe that I find it in a proximal portion of a large bone, which occupies this relation very appropriately. Its proximal superior subtriangular articular face is naturally associated with the already assumed anterior articulation of the ilium, and when so placed, presents outwards the smooth articular surface of the anterior part of the acetabulum.. It also pi esents forwards a narrowed process, and in line with the same posteriorly, a broad, vertical plate which is soon broken off, but which I suppose to have been continued but a short distance. The posterior process I suppose has been continued as the support of a slender pubis,* conform-ing in this respect to the type of birds. That there is very little trace of articulation for ischium behind the acetabulum is obvious, so that it is to be supposed that this element was small, vertically dilated proximally, and in contact with the pubis at the superior processes on the supero-external margin of the latter. *A suspieion whieh I at one time entertained, that the so-called pubis of the Croeodilia was homologous with the marsupial bones, has been removed, by reading Rathke's posthumous work on the development of the Crocodile.