148 



greatest number of ctaracters 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 vnth 

 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 in 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. 



