SIWALIK RHINOCEROTIDiE. 
35 
the anterior side being produced into a sharp process ; posteriorly to this process 
the external surface is convex, showing two faint ‘ costae ’ opposite the ‘ collis.’ 
The ‘anterior collis ’ is flattened internally, and throws off an oblique ridge to join 
the outer wall of the tooth : from the ridge connecting the ‘ posterior collis ’ with 
the outer wall, there is given off along ‘crochet,’ projecting into the ‘median 
valley.’ There is a distinct ‘ cingulum ’ on the anterior and posterior walls of the 
tooth. The third and fourth (penultimate and last) milk-molars resemble normal 
rhinoceros molars, and, therefore, require no detailed description. In the penul- 
timate tooth the ‘ crochet ’ is united to a small ‘ combing-plate,’ thus cutting off 
an ‘ accessory fossette.’ In both teeth there is a distinct ridge projecting from the 
hinder side of the * anterior collis ’ into the ‘ median valley,’ which may be called 
an ‘ anti-crochet.’ On the external surface of each tooth the anterior ‘ costa 5 
is placed close to the antero -external angle of the crown, which is produced into 
a sharp process, the two ridges tending to the formation of a ‘ buttress,’ which, 
however, is not so marked as in the true molars, the external surface being con- 
sequently less curved than in. the latter. The teeth are about the size of the upper 
milk-molars of R. sumatrensis , and, therefore, proportionately somewhat smaller 
than the true molars. A detached specimen, otherwise indistinguishable from the 
last tooth, has the anterior ‘ collis ’ without an ‘ anti-crochet ’ ; there is, therefore, the 
same variability in this respect in the milk-molars that we have seen to occur in the 
true molars. The specimen of a young maxilla of a rhinoceros represented in figure 
3 of plate XIX of Messrs. Baker and Durand’s memoir, containing the four 
milk-molars, probably belongs to the same species as the present specimen. The 
dimensions of the figured specimen will be found under the head of R. palceindicus. 
(p. 47.) 
Comparisons between milk-molars. — Erom the above description it appears 
that the milk-molars provisionally assigned to R. sivalensis differ from the true molars 
by the occasional presence of a ‘ combing-plate,’ and in the less development of 
the ‘ buttress ’ at the antero-external angle, and it is, therefore, incumbent on us 
to see whether analogous differences occur between the corresponding teeth of 
allied living species. There is unfortunately no specimen of the milk-molar den- 
tition of R. javanicus available to me ; but there are two skulls of R. sumatrensis 
(in which, as we have seen, the general form of the teeth is very like that of R. 
javanicus ) in the Indian Museum, showing the deciduous dentition. In one of 
these specimens a ‘ combing-plate ’ occurs in the penultimate milk-molar, as in our 
specimen of the milk-molars of R. sivalensis, and none in the last. In the two 
last milk- molars of the living species, the ‘ buttress ’ at the antero-external angle 
is less produced than in the true molars. Hence the external wall of the two 
milk-molars, when the teeth are in the jaw, is nearly coincident with the long axis 
of the skull, while in the true molars the corresponding surface forms a large 
angle with the same axis. If the last milk-molar of R. sivalensis were fully pro- 
truded, the outer surface of this and the anterior tooth would likewise be nearly 
