1876.] 



DENTAL CHARACTERS OF RHINOCEROSES. 



44.") 



conforms to the normal mammalian type, seen in PalcEotherium, 

 Tapirus, Equus, &c. It is that the post-glenoitl and post-tympanic 

 processes of the squamosal (fig. 1, pg and pt) do not unite below the 

 meatus auditorius (m), and that the latter is, as far as the squamosal 

 bone is concerned, a groove and not a canal, and the floor of the 

 meatus is formed solely by the tympanic ; whereas, in both existing 

 one-horned species (fig. 2) these processes (even in the newborn 

 animal) are in contact for a considerable space, and in old animals 

 are ankylosed together, so that the squamosal completely surrounds 

 the meatus as in elephant. The African rhinoceroses conform with 

 the Sumatran in this respect, though the groove is not so wide ; so 

 that this conformation of the squamosal may be said to characterize 

 all the existing two-horned species. 



Fis. 2. 



■3 \ Ti^ 



Side view of posterior part of skull of Rhinoceros sondaicus. One fourth 

 natural size. 



The letters as in fie. 1. 



A second character, but far less important, by which the skull of 

 the Sumatran Rhinoceros can be distinguished from that of its 

 Asiatic congeners is the backward position of the occipital crest, 

 which overhangs the nearly vertical occipital surface, whereas in 

 the others the latter slopes forwards and upwards from the condyles 

 to the crest (see figs. 1 and 2). 



The slight prominence for the second horn, situated rather an- 

 terior to the centre of the conjoined frontal bones, is another 

 diagnostic character. 



It is interesting to note that in all these characters, as well as in 

 Proc. Zooe. Soc— 1876, No. XXX. 30 



