468 THE VERTEBRATE SKELETON. 



much dilated. The squamosal is drawn out into a postglenoid 

 process, and the hamular process of the pterygoid is prominent. 

 The tympanic bulla is filled with cancellous bone. The mandible 

 is enormously large, the symphysis is long, the angle much 

 expanded and drawn out into a process which projects outwards 

 and forwards. 



Among extinct forms related to the Suina, Gyclopidius is 

 noticeable for having large vacuities in the lachrymo-nasal 

 region, while Cotylops has the postorbital bar complete ; both 

 these forms are from the North American Miocene. 



In the Tylopoda and Tragulina the skull resembles in most 

 respects that of the Ruminants, shortly to be described ; but it 

 is allied to that of the Suina in having the tympanic bulla filled 

 with cancellous bone. The tympanic bulla is better developed 

 in the Tragulina than in most Ungulates. 



Among Ruminants, the Bovidae, that large group includ- 

 ing the Oxen, Sheep, and Antelopes, as a rule have the face 

 bent on the basicranial axis much as in the Suina. The 

 parietals are generally small and early coalesce, the frontals 

 are large and are usually drawn out into horn cores, which are 

 however absent in the skulls of some domestic varieties of sheep 

 and oxen, and also in some of the earlier extinct forms of Bo- 

 vidae. These horn cores are formed internally of cancellous 

 bone, and on them the true epidermal horns are borne. In 

 young animals there is a distinct interparietal, but this early 

 fuses with the supra-occipital, and in the oxen also with the 

 parietals. The occipital crest is generally well marked, but 

 in the genus Bos becomes merged in a very prominent straight 

 ridge running between the two horn cores ; this ridge, which 

 contains air cells communicating with those in the horn cores, is 

 not nearly so well marked in Bison. There is often, as in Gazella, 

 a vacuity on the side of the face between the nasal, frontal, 

 lachrymal, and maxilla, but this is not found in oxen or sheep. 

 The prem axillae are small, the nasals are long and pointed, 

 and the turbinals are much developed. The Saiga antelope 



