398 Zoological Society. 



classification of the order Carnivora consist of peculiarities in respect 

 to certain of the foramina at the base of the cranium, I may perhaps 

 be permitted, although the foramina have already been to some extent 

 studied by those who have entered minutely into the details of 

 mammalian osteology, to point out some instances in other orders, 

 where, in the course of such observations as my opportunities have 

 permitted, I have noticed relationships between the peculiarities pre- 

 sented by the foramina and certain natural groups already established 

 by well-marked characters. 



For example, when we see that throughout the whole series of 

 Marsupial Mammalia — an order which, notwithstanding the widely 

 different modifications which its forms present, is marked by many 

 striking peculiarities of structure which quite isolate it from all other 

 members of the class — a number of minor peculiarities are equally 

 constant, and therefore in any species equally indicative of that j)ar- 

 ticular type of structure ; and among these, that the internal carotid 

 artery does not enter the cranial cavity, as in most mammalia, by a 

 foramen in the tympanic bone, nor — as is the case in many, and 

 might here be well expected, from the small development of the tym- 

 panic bone — through a fissure between that bone and the basi-sphe- 

 noid, but through a special foramen, which is pierced on the side of 

 the basi-sphenoid bone, and enters the skull in an inward and for- 

 ward direction, — we are surely justified in attaching some importance 

 to this peculiarity in a zoological point of view, and in considering it 

 just as characteristic of the Marsupial order as the articulation of the 

 head to the atlas by a double condyle is of the Mammalian class 

 itself. 



The remarkable differences in general structure presented by the 

 skull throughout the Rodent order, so carefully investigated and 

 judiciously applied to its classification in the researches of my accom- 

 plished friend Mr. Waterhouse, render it quite unnecessary to de- 

 scend to such minute and comparatively unimportant characters as 

 those which the foramina may afford ; and from the frequent imper- 

 fection of bony development in these usually small and rather lowly 

 organized mammalia, we cannot expect to find the characters pre- 

 sented by the foramina of so strictly definite a nature as those I shall 

 have to point out in animals of higher types of structure ; but never- 

 theless, when due allowance is made for these occasional imperfec- 

 tions of development, we shall yet find, that although the characters 

 of the foramina in this order are not sufficiently decided to be very 

 serviceable to the zoologist, they present a certain general accordance 

 throughout the groups, which in connection with the present subject 

 may perhaps give them some degree of interest. 



In this order, the canal, for which I here propose the name of ali- 

 sphenoid canal, and which serves to protect the continuation of the 

 external carotid artery during a part of its course, seems to be of 

 nearly constant existence, although in many species of the Hystricidce 

 it coalesces, through non-development of the separating lamina, with 

 the fissure passing through between the walls of the pterygoid fossa 

 into the orbit. The fissure alluded to, for which Mr. Waterhouse 



