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characters point out, than in many other orders; but at the same 
time, the general similarity of structure, to which I have before 
alluded, pervading the different modifications of form, has rendered 
it more than usually difficult to find characters truly essential, and 
independent of adaptive differences, on which to found truly natural 
subdivisions. These characters, when found in such an order as tlie 
Carnivora, we may fairly presuppose to be minute, and such of them 
as I have been able to discover, and which I have found to be con- 
stant so far as my opportunities of observation have extended, it is 
my object here to point out; with regard to the foramina, there is 
one which seems to be very characteristic of the order itself, since 
even in the true Bears, in which it does not exist as a canal, it is 
represented by a very well-marked groove. In other Carnivora it 
consists of a canal situated on the inner surface of the exoccipital 
bone usually running from before backwards and downwards; it 
gives passage to a vein; and if a special name should at any time be 
deemed requisite, perhaps that of exoccipital canal may be found 
suitable. ‘The characters of which I purpose to make more or less 
use in the subdivision of the order, are the structure of the ptery- 
goid bones and processes, the presence or absence of the ali-sphenoid 
canal, the form of the auditory bulla, and the course of the internal 
carotid artery through its canal, the structure of the mastoid and 
paroccipital processes, the situation of the foramen condyloideum, 
and to some extent, the structure of the lower jaw. It is by the 
fortunate circumstance of possessing in my own collection, crania 
representing all the leading divisions of the order, that I have been 
enabled, in the first instance, to remark the differences presented by 
the characters alluded to; but excepting a few genera, which I have 
been enabled to examine in the museums of the College of Surgeons 
and of this Society, it is only in the excellent series of skulls con- 
tained in our National Museum that I have been able to collect 
evidences of their constancy. Such being the limits of my oppor- 
tunities of observation, it cannot be expected that I should give 
an opinion as to the precise zoological station of every one of the 
numerous genera; I will therefore take as a standard system the 
classification made use of in the List of Mammalia published by 
Mr. Gray, by order of the Trustees, since in the principal divisions 
it accords pretty nearly with my own ideas; simply pointing out 
where I find any genus whose cranium I have examined which I 
think requires to be altered in its position, and at the same time 
assigning to the divisions characters of my own, and expressing my 
opinion as to their rank. 
Although in that classification the Bears are placed near the ter- 
mination of the series, yet I believe it to be most usual to reverse 
the order and to begin with them; therefore I will first point out 
the characters which they present, and in so doing will confine 
myself to the genus Ursus, the subfamily Ursina of Mr. Gray. We 
here find no trace of a pterygoid fossa, the outer pterygoid process 
being closely pressed against the inner one, or true pterygoid bone, 
and sending off a strong lamina of bone to enclose the ali-sphenoid 
