OCR Text |
Show 1866.] MR. ST. GEORGE MIVART ON MICRORHYNCHUS. 155 Externally there is a mere rudiment of a cingulum ; but internally it is exceedingly developed both in front and behind, but especially the latter, where it constitutes a distinct, though small, basilar process, or talon, almost as marked, indeed, as in the two premolars behind it. Inside of left upper canine and premolars. Scale, twice nat. size. From the middle of the internal surface a strong vertical prominence is developed, which extends from the cingulum down to the apex of the tooth; in front of this is the small anterior process, which projects forwards from the middle of the anterior margin of the tooth, greatly increasing its antero-posterior diameter, and presenting a character absolutely peculiar to this species of the Lemu-roidea. In Hapalemur it is rather longer relatively, and considerably exceeds the most anterior premolar in size. In Indris the canine is even slightly more prolonged as compared to the premolar than in Hapalemur, and decidedly so in Propithecus. In M. laniger the canine and most anterior premolar are more equal than in any other Lemuroid*, or indeed than in any other Primate except Man. This canine is exceedingly like the first premolar of Lemur. The anterior upper premolar is unicuspidate, and resembles the canine, except that it is less vertically extended; while the process from its anterior margin is much larger. The cingulum also is rather more marked externally. This tooth differs from the corresponding one of every other species of the suborder; but most resembles the homologous one of Indris, which, however, has the anterior process rudimentary. It slightly resembles the second premolar of Lemur and Hapalemur, but is more antero-posteriorly and less transversely extended. The posterior upper premolar is like the preceding, except that it is smaller in all dimensions except width from within outwards, and that the posterior basilar process is shorter, while the internal cingulum is much more marked. This tooth has the same resemblances and differences to its homologue in Indris as that last described has to its representative in that genus. It resembles the second premolar of Lemur and Hapalemur more than the anterior premolar does ; and it much more resembles the second than it does the third premolar of any Lemuroid. The first upper molar is very different from the premolars, and is the largest grinding-tooth in the upper jaw. There is more difference in size between it and the posterior premolar than there is between any other contiguous grinding-teeth of the upper jaw, as also is the case in Indris. * I. e. anv other species of the suborder Lemuroidea. |