470 THE VERTEBRATE SKELETON. 



and the lachrymal fossa is large in the Cervidae and the Griraf- 

 fidae except Sivatherium. The vacuity between the frontal, 

 lachrymal, maxilla, and nasal is specially large. 



The hyoid of Ruminants is noticeable for the development 

 of the anterior cornua, which include stout and short cerato- 

 hyals and epi-hyals, long and strong stylo-hyals and large 

 tympano-hyals which are more or less imbedded in the tym- 

 panics. 



PERISSODACTYLA. In the skull of Perissodactyles an ali- 

 sphenoid canal is found and the nasals are expanded behind. 

 Among the living animals belonging to this group the skull least 

 modified from the ordinary type is that in Rhinoceros. In this 

 form the skull is considerably elongated, the facial portion being 

 very large. The occipital region is elevated, but the cranial 

 cavity is small, the boundary line between the occipital and 

 parietal regions being drawn out into a prominent crest, which 

 is occupied by air cells. There is no postorbital process to the 

 frontal, and the orbit is completely confluent with the temporal 

 fossa. The nasals are fused together and are very strongly 

 developed, extending far forwards, sometimes considerably 

 beyond the premaxillae. In some extinct species, such as Elas- 

 motherium and the Tichorhine Rhinoceros, R. antiquitatis, the 

 mesethmoid is ossified as far forwards as the end of the nasals. 

 The nasals are arched and bear one or two roughened surfaces 

 to which the great nasal horns are attached. The premaxillae 

 are very small and the pterygoids are slender. The palate is 

 long, narrow, and deeply excavated behind. The postglenoid 

 process of the squamosal is well developed, and generally 

 longer than the paroccipital process of the exoccipital. The 

 tympanic and periotic are both small and are fused together. 

 The condyle of the mandible is very wide, the angle rounded, 

 and the coronoid process moderately developed. 



In the Titanotheriidae, a family of extinct Perissodactyla 

 from the Miocene of North America, the occipital region is much 

 elevated, as is also the fronto-nasal region, the nasals (perhaps 



