RHINOCEROTIDA. 403 



aborted, so that the contour of the crown is triangular. Head 

 large, skull elongated, elevated posteriorly into a transverse occi- 

 pital crest. No postorbital processes. Nasal bones large and stout, 

 co-ossified, and standing out freely above the premaxillae, from which 

 they are separated by a deep and wide fissure ; the latter small, 

 generally not meeting in the middle line^in front, often quite rudi- 

 mentary. Tympanics small, not forming a bulla. Brain cavity very 

 small for the size of the skull. Vertebrae: C 7, D 19-20, L 3, 

 S 4, C about 22. Limbs stout, and of moderate length. Three 

 completely developed toes, with distinct broad rounded hoofs on each 

 foot (Fig. 151, p. 368), some fossil forms having a fourth in the 

 manus. Eyes small. Ears of moderate size, oval, erect, prominent, 

 placed near the occiput. Skin very thick, in many species thrown 

 into massive folds. Hairy covering scanty. When one horn is 

 present it is situated over the conjoined nasal bones ; when two, the 

 hinder one is over the frontals. These horns, which are of a more 

 or less conical form and usually recurved, often grow to a great 

 length (three or even four feet), and are composed of a solid mass 

 of hardened epidermic cells growing from a cluster of long dermal 

 papillae. The cells formed on each papilla constitute a distinct 

 horny fibre, like a thick hair, and the whole are cemented together 

 by an intermediate mass of cells which grow up from the interspaces 

 between the papillae. It results from this that the horn has the 

 appearance of a mass of agglutinated hairs, which, in the newly 

 growing part at the base, readily fray out on destruction of the 

 softer intermediate substance ; but the fibres differ from true hairs in 

 growing from a free papilla of the derm, and not within a follicular 

 involution of the same. 



The large lower cutting 

 teeth of the typical Rhino- 

 ceroses have been very gener- 

 ally regarded as incisors, but 

 comparison with fossil allied 

 types, in which three lower in- 

 cisors and canines are present, 

 leaves little doubt but that 

 they are really canines. The 

 upper molar teeth present some 



amount of Specific Variation ; FIG. 16S. A partially worn second right upper 

 .1 ^.i,:!^ /TV molar of (A) Rhinoceros sondaicus, and (B) R. uni- 



thus while one type (Fig. ^^ fc ; F ; ssette cut off from media n valley ; m> 



168, A} has Only a' simple crotchet; n, crisis, or corabing-plate ; , anterior 

 " Crotchet " projecting from valle y : *> anterior intermediate column. Other 

 ,i . j letters as in Fig. 155, p. 375. 



the posterior transverse ridge 



into the median valley, in others (Fig. 168, ) this crotchet joins a 

 " crista," or " combing-plate," projecting from the outer wall to cut 

 off a distinct f ossette from the median valley. Occasionally, however 



