234 ON THE EXTINCT MAMMALIA OF 



Avidth. A similar ai'ticulatiou of the intermaxillary with the nasal bone exists in 

 the allied recent genus Hyrax, but not in the true Rhinoceroses. 



The nasals, even in aged specimens of Hyracodcm nehrascensis, remain separated. 

 Their anterior free ends appear to have projected about an inch beyond their articu- 

 lation with the intermaxillaries. 



There are no evidences whatever in favor of Byracodon having possessed either 

 a frontal or a nasal horn. The surface of the forehead is smooth, and presents no 

 prominence adapted to the support of a horn. The nasal bones become narrow and 

 comparatively weak in front, and apj^ear totally unadapted to sustain a weapon 

 like the nasal horn of existing Rhinoceroses. 



Posterior view of the sJcidl. — The inion forms a nearly equilateral triangle, of which 

 the mastoid processes form the basal angles. The occiput is proportionately more 

 bulging in the median line than in the Indian Rhinoceros, but is less so than appears 

 to be the case in R. occidenialis. The condyles have their long diameter more nearly 

 vertical than in the former, but less so than in the latter. They are prolonged be- 

 neath in a scroll-like manner on the basilar process, and approach in this position at 

 the distance of a line from each other. 



The occipital foramen is low pyrifomi, and about ten lines in diameter. It has its 

 upper margin considerably posterior to the position of the lower one. 



Base of the skull. — The co-ossified basi-occipital and sphenoidal resemble those of 

 the Indian Rhinoceros, becoming narrower and more prominent and convex anteriorly. 



The paramastoid process is longer than the mastoid and post-glenoid processes. , 

 The mastoid is shorter than the last named process, and is separated from it by a 

 wide interval. 



The condyloid foramina are situated just to the outside of the lower ends of the 

 occipital condyles, and are ten lines apart. 



The foramen lacerum is a large reniform vacuity, about an inch fore and aft and 

 the third of an inch wide. In advance of it a short distance is the foramen ovale. 

 Half an inch from this, to the outside of the root of the ptcnrygoids, is a foramen or 

 short canal communicating with the spheno-orbital foramen. The latter occupies a 

 position at the apex of the orbital cavity, internal to a pointed process terminating 

 the orbito-temporal ridge. 



The optic foramen is situated about an inch in advance of the spheno-orbital 

 foramen. 



The glenoid articular fossa forms a deep concavity opening outwardly and back- 

 wai'd on the posterior root of the zygoma. It is deeper than in the Indian Rhinoce- 

 ros, and directed more backward at its outer part. The post-glenoid process is 

 comparatively short, thick and tuberous. 



