1880.] Prof. Huxley. Epipubis of the Bog and Fox. 163 



in 1871, in all four. And the only phrase which appears to require 

 modification in that description is the use of the term fibro- cartilage. 

 I do not remember whether, formerly, I submitted the structure to 

 microscopic examination or not ; but in the specimens lately examined, 

 notwithstanding the firmness and density of the triangular plate, it 

 contains no true cartilage cells, but is entirely composed of fibrous 

 bands which lie parallel with one another in the middle of the plate, 

 while, at the thickened edges, they become closely interwoven. 



A comparison of this triangular fibrous plate in the fox, with the 

 "marsupial " bones of Phalangista vul/pina, shows that the fibrous plate 

 in the former animal exactly answers to the basal part of the " mar- 

 supial " bone in the latter. It may properly, therefore, be termed the 

 epipiibic ligament, and must be regarded as a structure of the same 

 order as the rudimentary clavicle and the rudimentary hallux of the 

 Canidce ; that is to say, as the remains of an organ which was fully 

 developed in the ancestral forms of that group. 



It is interesting to remark, in connexion with this interpretation of 

 the facts, that, in the existing Thylacinus, which presents so many 

 curious points of resemblance to the dogs, the epipubis is not ossified. 

 As, however, the Canidce have certainly existed since the Eocene 

 epoch, there is no likelihood of the existence of any direct genetic 

 connexion between the dogs and the Thylacines. The existing carnivo- 

 rous Marsupialia have evidently all proceeded from ancestral forms, 

 characterised by the possession of a thumb-like hallux, a peculiarity 

 which is presented neither by the dogs, when they possess a hallux, 

 nor by any other Carnivora with pentadactyle hind feet. Moreover, 

 the early birth of the young and the development of a marsupium in 

 the female, are evidences of the departure of the existing Marsupialia 

 from the direct line by which the Mammalia have advanced from the 

 ornithodelphous type. That the ancestors of all mammals possessed 

 bony or cartilaginous epipubes is, I think, highly probable, but it 

 does not follow that they had the marsupial method of bearing and 

 nourishing their young. 



