236 



Prof. H. G. Seeley. 



[Dec. 8, 



the genus Hyla ; such absence, considered with the presence of a pubis 

 in Dactylethra, would support the conclusion that the pubis and ilium 

 are connate in Anura. 



In the young of Crocodilia the same three elements contribute to 

 the formation of the articular cup for the femur, the ilium above, the 

 ischium behind, and a cartilage in front. 



Professor Hoffmann* regarded this cartilage as the pubis, and then 

 the bone which is. anterior to it, and had previously been identified as 

 the pubis, became the pre-pubis. 



, • Professor Huxley questioned this identification, and regarded the 

 bone as the ossified part, and the -cartilage apparently as the unossified 

 portion of the pubic element of the pelvis. | This cartilage is well 

 known to decrease in dimensions with the age of the crocodile, but it 

 does not disappear by augmenting the extent of the supposed pubic 

 bone ; though if it were really a pubic cartilage, its ossification should 

 cause the anterior bony element to extend into the acetabulum. But 

 instead of disappearing in this way, ossification has the effect of contin- 

 uing to exclude the supposed pubic bone from the acetabulum; so that 

 the cartilage in the young animal does not give rise to a separate osseous 

 element in the adult, but disappears by so ossifying as to approximate 

 the ischium and ilium. At first there is a gap between the ischium and 

 ilium anteriorly, which the cartilage fills, but eventually in old animals 

 these bones almost meet each other, and the cartilage is ossified. Thus 

 in the adult animal the acetabulum is formed by two bones, one being 

 the ilium, and the other in the position otherwise occupied by the 

 ischium and pubis. Therefore it follows, either (1) that the pubic 

 cartilage, if originally distinct in the young, becomes incorporated 

 by ossification with the ilium and ischium ; or that (2) the pubis in 

 crocodiles does not enter into the acetabulum, but is a pre-ac stab alar 

 ossification. I am aware of no exception to the law that the pubis 

 contributes to the os innominatum when it has a separate existence, 

 and therefore it seems to me more probable to suppose that ischium 

 and pubis should be connate, like the same elements in some sala- 

 manders, and undivided, than that crocodiles should so differ in plan 

 of the skeleton, as to have the pubis removed from connexion with 

 the ilium, and from the acetabulum. If the former view prevails, then 

 the acetabular cartilage in crocodiles is never a pubic cartilage, but 

 only the unossified part of the ilium or ischio-pubic bone which 



* < Niederl. Archiv Zool.,' vol. 3, 1876, p. 144. 



t ' Roy. Soc. Proc.,' vol. 28, 1879, p. 394. Prof. Huxley's language i3 not quite 

 clear on this point. He says (p. 398) " It is the osseous portions of the pubes 

 which are commonly described as the entire bone." " These apparently anomalous 

 elements of the pelvis are readily moveable upon their fibrocartilaginous connexions 

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

 pubes.' ' 



