148 
greatest number of characters are presented at one view, and for the 
study of which I have had the most ready opportunities ; and I now 
propose to offer such results of my observations as I have been able 
sufficiently to mature: In pointing out the characters of the skull 
which distinguish these two grand divisions of the Ungulata, the 
differences will appear more striking if I consider the Perissodactyla 
as they are restricted by Prof. Owen, namely exclusive of the Pro- 
boscidian and other aberrant forms, which, though they agree with 
them in the most essential characters, differ in many points of confor- 
mation. 
The nasal bones in the Perissodactyla are gradually widened behind, 
so that their posterior angles approach the anterior margins of the 
orbits, between which the suture which separates them from the 
frontals runs more or less directly across the skull; we may naturally 
expect such a character to be masked by the singular modification 
which these bones undergo in the Tapir; but in the Artiodactyle di- 
vision, even though the extreme points of the nasal bones occasionally 
extend very high, or as in the Llama, and in the genus Cephalophorus 
among the Antelopes, a sudden extension from their outer edge de- 
scends a little on each side of the face, this decided character is never 
manifested. 
The intermaxillary bones in the Perissodactyla, if there be teeth 
developed in their median portion to a functional size, are always 
deep enough to allow them to be vertically implanted, while in the 
Artiodactyla, the teeth when existing m this bone always incline 
towards each other, their roots being divaricated to allow the nasal 
opening to extend down between them. In this group, with the 
singular exception of the genus Hippopotamus, we find a distinct fo- 
ramen above the orbit for the passage of the supraorbital nerve, with 
a groove extending from it down the face ; while in the Perissodactyla, 
it would appear as though this nerve would issue at a point more 
towards the outside, since the foramen only exists in the Horse, in 
which it is placed quite at the commencement of the postorbital pro- 
cess, and has no groove continued from it. 
In the interior of the orbit, there is always, in the Artiodactyla, an 
increased concavity of surface upon the anterior side about the junction 
of the lacrymal and frontal bones; and in the middle of this fossa, 
upon the edge of the lacrymal somewhere between the ductus ad 
nasum and the entrance of the infraorbital canal, a pit, most strongly 
marked in the Hogs, which serves, as I have found in the Sheep, for 
the origin of the obliquus inferior muscle of the eye, the remainder 
of the fossa being filled up with adipose matter. In the Perissodac- 
tyla no such fossa exists, and there is never more than a very slight 
depression marking the origin of the muscle, in most cases not per- 
ceptible at all. The shortening of the bony palate in the latter group, 
the small difference of level between it and the base of the cranium, 
together with the longitudinal extension of the posterior nasal orifice, 
the lateral spreading-out of its walls and the constant existence of the 
alisphenoid canal, which I pointed out in my former communication, 
may be again adverted to. 
