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Show 1S76.] DENTAL CHARACTERS OF RHINOCEROSES. 445 conforms to the normal mammalian type, seen in Palaotherium, Tapirus, Equus, &c. It is that the post-glenoid and post-tympanic processes of the squamosal (fig. 1, pg and pt) do not unite below the meatus auditorius (ni), 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 iu 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. Fig. 2. Side view of posterior part of skull of Rhinoceros sondaicus. One fourth natural size. The letters as in fig. 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 anterior 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. ZOOL. Soc-1876, No. XXX. 30 |