64 
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 par- 
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 Hystricide 
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 . 
