OCR Text |
Show 448 PROF. W. H. FLOWER ON THE CRANIAL AND [May 16, In the former, besides the greater general size and greater length and height of the cranium as compared with breadth, the ascending ramus of the mandible is considerably higher in proportion (a character much relied on by Blyth),so that the whole skull, when mounted upon the lower jaw, is more elevated. The occipital surface also is markedly higher and narrower than in R. sondaicus. But in addition to these well-known and obvious characters, there are certain features in the conformation of the base of the skull which are eminently characteristic of the two species, and which when once recognized cannot be mistaken, and are superior for diagnostic purposes to those derived from the general form and proportions, or from parts of the skull the form and dimensions of which are influenced by muscular development, the size of the horns, & c , and consequently very liable to individual variation. In R. unicornis (fig. 3) tbe mesopterypoid fossa is always narrower than in R. sondaicus (fig. 4) ; and the same condition extends backwards throughout the basi-sphenoid and basi-occipital bones, not only relatively to the size of the skull, but absolutely, the point of junction between these two bones being, in large skulls of R. unicornis, actually narrower from side to side than in much smaller specimens of R. sondaicus, though generally making a more salient projection downwards. Furthermore, the free ends of the pterygoid processes (pt) are compressed and deeply grooved in B. unicornis, whereas in R. sondaicus they are more flattened and laterally expanded. The hinder margin of the palate is more regularly concave in the former, and has a projection in the middle line in the latter. But the most absolutely diagnostic structural difference is seen in the hinder end of the vomer (vo), which in B. unicornis is thickened and firmly united by its sides to the base of the pterygoid processes, while in R. sondaicus it is thin, lamelliform, pointed, and free, so that in museum specimens it is very often injured or destroyed. The upper molar teeth of R. unicornis and R. sondaicus are remarkablv unlike for species otherwise so nearly related * ; but the same kind of difference exists between the two best-distinguished species of the African forms, R. simus and R. bicornis ; so that the characters of the teeth alone, which have been so much relied on in the case of the extinct species, are not, when taken by themselves, good tests of affinity. In R. unicornis, in the first and generally in the second molar, the crochet (or posterior combing-plate) (ci1) curves forwards and usually unites with the crista (anterior combing plate) (c1) developed from the lamina, so as to cut off an " accessory valley " (a) from the extremity of the median sinus •j**. The premolars and milk-molars present a * Professor Owen says truly in his 'Odontography,' p. 594 (1845):-" Even in existing species so nearly allied as the unicorn Rhinoceroses of India and Java, each might be determined hy a single detached molar tooth." But his views must have been subsequently modified; for in the descriptive catalogue of the Museum of the College (1853), the skulls of both species are described under the common name of R. indicus. t For an explanation of these terms see Busk, P. Z. S. 1860. p. 410. "Notice |