94 



THE EXTINCT BATRACHIA, REI'TILIA 



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 vertebras thus 

 form a massive column, which no doubt supported the weight of these monsters. That 

 the ischia performed this function in part in Lselaps, 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 lace, 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 inwards as well as downwards. This adds still fur- 

 ther to the peculiar ensemble of characters of these Dinosauria. 



This relation has already been described as the true one, by Lcidy. 



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. 



PMs. 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 presents 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 dement 

 was small, vertically dilated proximally, and in contact with the pubis at the superior 

 processes on the supcro-extcrnal margin of the latter. 



* A suspicion which I at ono time entertained, that the so-called pubis of the CrocodlUa was homologous with 

 tho marsupial bones, has been removed, by reading Rathke's posthumous work on the development of the Crocodile. 



