FOSSIL REPTILES. 217 



not separated from the anterior sphenoid. Its great wings are 

 similarly situated, and perform the same functions as in mam- 

 malia ; but they always remain separated from the body of the 

 bone, as in the foetus of that class. They embrace a great part 

 of the space and functions of the orbital wings, of which last 

 no vestiges remain, except some little points of detached ossifi- 

 cations in the membrane which closes this part. 



The pterygoid wings are similarly situated, and perform 

 similar functions as in the mammalia. But they always remain 

 separated from the body of the bone, and unite below to prolong 

 the nasal tube, as in the ant-eaters. 



The situations and functions of the tympanic bone are the 

 same as in mammalia, but it gives the facet for the articulation 

 of the lower jaw. So are those of the mastoid, but its processes 

 are rather more extended than in mammalia. The place and 

 offices of the os petrosum are the same, only that the labyrinth 

 extends into the neighbouring bones. 



Between the osseous box of the tympanum and the jugal 

 bone, is one which can only correspond with the zygomatic of 

 the temporal bone ; and between the pterygoid wing and the 

 jugal and maxillary bones, is another, which corresponds, but 

 feebly, to an external pterygoid apophysis of the sphenoid, 

 which would be entirely detached from its principal bone, a 

 thing which never occurs in mammiferous animals. Thus we 

 see that all the essential differences are reduced to this distinc- 

 tion and division of the frontal bone. 



In consequence of the importance of this head, we have been 

 a little more extended in our remarks upon it. In our subse- 

 quent anatomical details we shall be as brief as is consistent 

 with perspicuity, noticing what is of chief import only. 



We have before mentioned, that an apophysis of the tym- 

 panic bone forms a facet for the articulation of the lower jaw. 

 This facet forms a gynglymus of no great depth. In the mam- 

 malia, even in the foetus state, as soon as the lower jaw has 

 acquired any consistence, it presents but one bone on each 



