1887.] 



On the Os Pubis in Crocodilia. 



241 



being anterior in position to the acetabulum, and in similar isolation 

 from the ilium. 



In the current identification of this bone every consideration has 

 been made subordinate to the embryological evidence as stated by 

 Rathke. Yet although his excellent description unaccompanied by 

 figures has been regarded as conclusive that the bone under discus- 

 sion is the pubis, it seems to me necessary to reconsider the evidence 

 before the matter can be thus settled. The pelvis of a crocodile in 

 that stage of development which corresponds with the middle period 

 of incubation, if I rightly interpret the author's meaning, is appa- 

 rently more like that of an emu than is the adult animal in so far as 

 the ischium and pubis are concerned ; while the relative shortness 

 of the pubis is suggestively Iguanodont. 



Rathke's statement is as follows : the ilium, ischium, and pubis of 

 each side unite to form a single unbroken cartilaginous mass. The 

 two ilia are short, rather broad, plates, as in the full-grown animal, 

 and extend somewhat outward beyond the transverse processes of the 

 sacral vertebra?. The ischia were also similar to those of the full- 

 grown animal, consisting of tolerably thick plates, somewhat 

 expanded transversely at their median union, but are not so broad in 

 proportion to their length as in the full-grown crocodile. The pubis 

 was somewhat shorter than the ischium, and in proportion to the 

 other parts of the pelvis was much shorter than in later life, and not 

 directed so much forward. It extended downward nearly parallel to 

 the ischium, almost along its whole length, only separated from it 

 by a small interspace, and uniting with it at its upper end. Ventrally 

 the pubes are widely separated, and have the hinder small half of the 

 connexion with the yolk-sac opening between them. They preserved 

 a similarity in shape to that of the mature crocodile, but the distal 

 ends were not so wide in proportion to their length, and the other 

 parts are not so slender as in later life. And on a subsequent page 

 the author again remarks, " The direction of the pubis in embryonic 

 life remains different to that of the adult, but in the middle of the 

 embryonic period there comes to be a division in the cartilaginous 

 plate which hitherto had represented the ilium, ischium, and pubis." 



The early condition of the pelvic elements is so interesting in its 

 parallelism of the ischium and pubis, and in the subsequent change 

 of direction of the reputed pubis, that I applied to Professor W. K. 

 Parker, F.R.S., for help. He at once sent me three examples of 

 Crocodilus palustris, one about mature in the egg, another with the head 

 o cm. long, the body about 4*5 cm., and the tail about 7 cm., which 

 was about half grown, and a smaller specimen about a third grown. 



On' examination I found that the pubes in the half-grown specimen 

 were developed as in the adult, even to the fibrous extensions in front 

 of the bones and behind them, and the only important difference was 



