OCR Text |
Show 1876.] DENTAL CHARACTERS OF RHINOCEROSES. 449 similar conformation, subject to individual variation. This never takes place in the true molars of R. sondaicus (though it may occasionally in some of the milk-molars, especially the second), as in fact the crista is rarely developed in that species, and the crochet is a simple straight free process in the true molars, though often double in tbe premolars. On the other hand the molar teeth of R. sondaicus and R. sumatrensis are remarkably alike. Mr. Busk, it is true, has pointed out characters by which they can be distinguished* ; but they are such as to require great attention on the part of the observer to detect, and one of them, the difference in the relative length and breadth, does not appear to m e to bear the test of application to a considerable series of individuals. I may, however, add another, which appears to be tolerably constant, viz. the greater depth of the posterior as compared with the median sinus in R. sumatrensis, whence it results that in an extremely worn tooth of the latter there are always two fossse, the median and posterior, while in R. sondaicus the posterior disappears, leaving finally only a single fossa in the wide surface of exposed dentine. In R. unicornis, in a corresponding stage of attrition, there are three fossa-the median, accessory, and posterior. The premolars of R. sumatrensis can be distinguished from those of R. sondaicus by the complete absence of the double crochet above mentioned as usually, if not always, present in the latter. It is a curious circumstance that the remains of R. sondaicus, though more recently distinguished as a distinct species, are more abundant in our collections than those of R. unicornis. In the Col-lege- of-Surgeons Museum there are 9 skulls of this species, and 5 of R. unicornis. In the British Museum the numbers are respectively 9 and 7. This may be accounted for by the geographical range of the species, as it is R. sondaicus which inhabits the Bengal Sunderbunds, and the neighbourhood of Calcutta, while R. unicornis is only known from the hilly country to the north, bordering upon Nepal, Bhotan, and Assam. On the other hand, judging from the figures, nearly all the living examples of rhinoceroses brought to this country before the present specimen of R. sondaicus, which was acquired by the Society in 18/4, have belonged to the species which we call R. unicornis; but this is a subject which has been discussed in Mr. Sclater's article on the species of Bhinoceros living in the Society's Gardens, shortly to be published in our ' Transactions ' with magnificent illustrations of external characters of five species drawn from life. To return to the collection of skulls. Judged by the tests above given, and by other characters more difficult to describe, but easily appreciated on an examination of the specimens, the one described of the Discovery at Sarawak, in Borneo, of the fossilized Teeth of Rhinoceros." In one of tbe specimens of R. unicornis in the British Museum, though the crochet and crista are well developed, there is no actual union of their extremities. * Loc. cit. |