1879.] Characters of the Pelvis in the Mammalia, fyc. 399 



are readily moveable upon their fibro- cartilaginous connexions with the 

 acetabulum. But in no essential respect do they differ from ordinary 

 pubes. Throughout their whole length they give attachment to a 

 muscle, which answers to the pectineus and short adductors of the 

 thigh, while the aponeurosis which lies between them and the ischia 

 gives origin as usual to the obturator externus ; and the obturator 

 nerves pass out close to the cotyloid ends of the pubes (Plate 8, fig. 12, 

 Ob. n.). For the trowel-shaped forward continuations of the pubes on 

 each side of the symphysis, I will adopt the name of epipubes, proposed 

 by Hoffman for other structures which J believe to be homologous 

 with them. They are firmly connected with the aponeurosis of the 

 external oblique muscle, in which, just in front of their outer edges, lie, 

 on each side, the first set of abdominal false ribs (Plate 8, fig. 12, r). 

 In short, in all their most important relations, these appear to me to 

 be structures homologous with the marsupial bones of the Monotremes 

 and Marsupials, which in Thylacinus are represented by mere cartilages. 

 But although homologous, they are very different in detail ; and, in all 

 other respects, the Crocodilian pelvis departs even further than that 

 of the Chelonia and Lacertilia from the Mammalian type. 



The Pterosauria seem to have possessed epipubes ; and in the Dicy- 

 nodontia there is an approximation to the backward elongation of the 

 subsacral part of the ilium which is characteristic of Mammals ; but, 

 in both these groups there appears to have been no obturator fonta- 

 nelle. 



In the ornithoscelidan reptiles and in birds (Plate 8, figs. 7, 8, 

 and 9), the pelvis, starting from the lacertilian and crocodilian type, 

 undergoes a series of modifications of a new character, the ultimate 

 result of which is a pelvis as much specialized as that of the higher 

 Mammals, but totally different from it in principle. 



The broadening of the ilium seen in" the crocodile increases, so that 

 the antero-posterior length of the bone eventually becomes very great, 

 chiefly in consequence of the elongation of the prseaxial region of the 

 ilium. But, with all this, the direction of the iliac axis does not sensibly 

 change, and it remains more or less inclined downwards and forwards 

 (Plate 8, fig. 9). The inner wall of the acetabulum is largely membra- 

 nous. The iliopectineal axis becomes slightly inclined to the sacral axis, 

 but never so much even as in Echidna. The main change in the pelvis 

 is, in fact, effected by the extraordinary elongation of the pubes and the 

 ischia, and their rotation backwards and upwards ; while, at the same 

 time, the symphysial union of the bones of opposite sides altogether 

 disappears. In Rhea, the ischia unite with some of the post-sacral 

 vertebrae as they do in many Mammalia. The pubis becomes very 

 slender and, as it lies parallel with the ischium, the obturator space is 

 the development of the crocodile's pelvis affords conclusive evidence respecting the 

 homologies of the pubes in these animals. * 



