XI.] PERISSODACTYLA. 191 



The hyoid is much like that of the Horse, and has a 

 glossohyal process from the middle of the basihyal. 



The Tapirs present some singular modifications of the 

 same type of skull. 



As in the Rhinoceros, there is no separation between the 

 orbit and temporal fossa, but the anterior nares are of 

 immense size, and extend backward above the orbits, being 

 separated from them only by a thin plate of bone instead 

 of a broad flat surface, as in the Horse and Rhinoceros. 

 The nasal bones are short, broad behind, pointed in front, 

 much elevated, and supported by a tolerably well ossified 

 mesethmoid, which spreads out laterally at its upper end. 1 

 The inferior and lateral margins of the great narial apertures 

 are entirely formed by the maxillae, which extend up to meet 

 the nasals, the premaxillx not taking any share in them. The 

 ethmo-turbinals are small, while the maxillo-turbinals, on the 

 other hand, are very extensive, though their plications are 

 comparatively simple. A conspicuous feature in the upper 

 part of the face is a groove, which extends backwards on 

 the side of the dilated hinder end of the nasal bone, and 

 curves inwards to form a rounded depression over the naso- 

 frontal suture. The form and size of this depression vary 

 in different species. It lodges an air sinus, with cartilaginous 

 walls extending upwards from the nasal chamber. In front 

 of the nares the rostrum formed by the maxillsi with the 

 premaxillna in front is produced, compressed anteriorly, and 

 curved downwards. 



The base of the cranium resembles generally that of 

 the other Perissodactyla. There is an alisphenoid canal, and 



1 In one species ( T. Dairdii) the ossification of the mesethmoid extends 

 far in advance of the nasal bones, and is clasped and suppDrted below 

 by ascending plates from the maxillae. 



