igo THE SKULL. [CHAP. 



horizontal plates of the palatines being very narrow. The 

 pterygoids are very slender, as in the Horse, but placed more 

 vertically. There is a distinct alisphenoid canal. The 

 squamosal sends down a very long, conical, postglenoid 

 process parallel with, and equalling, or sometimes exceeding, 

 in length, the paroccipital process. In all existing two- 

 horned species (7?. sumatrensis, bicornis and simus) the 

 meatus auditorius lies in a deep groove between the post- 

 glenoid and the post-tympanic processes of the squamosal. 

 In the one-horned species (R. unicornis and sondaicus) these 

 processes unite below so as to completely surround the 

 meatus. The post-tympanic process articulates with the 

 exoccipital, completely excluding the mastoid from the 

 external surface of the skull. 1 



The tympanic and periotic are ankylosed together, but 

 not with the squamosal. They are both very small. The 

 under surface of the tympanic is rough, forms no distinct 

 bulla, and is much encroached upon posteriorly by the very 

 large tympanohyal, which presents a circular, slightly concave, 

 rough, inferior surface, half an inch in diameter (in an adult 

 Sumatran Rhinoceros). Externally, the tympanic is pro- 

 duced into a rough, irregular, inferior wall to the auditory 

 meatus. The periotic internally shows the internal auditory 

 meatus near its lower part, but no distinct depression for 

 the flocculus ; it is prolonged upwards and outwards into 

 a small mastoid portion, which, as before said, does not 

 appear on the outer surface of the skull. 



The mandible has a very wide condylar articular surface, 

 and slender recurved coronoid process, a rounded, somewhat 

 incurved angle, a compressed, rather narrow, horizontal por- 

 tion, and a shallow depressed symphysis. 



1 See W. PI. Flower, " On seme Cranial and Dental characters of the 

 existing species of Rhinoceros." (Proc. Zool. Soc. 1876.) 



