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Show 1882.] MR. W. N. PARKER ON THE INDIAN TAPIR. 775 entirely within their sockets. The last upper and lower deciduous molars had evidently only just come into place. De Blainville * gives a description of several stages in the development of the Tapir's teeth ; but he is not at all clear on one or two important points, which I now hope to explain. On cutting into the jaws, distinct germs of the first and second premolars were seen, in the form of small conical cups, one for each main cusp; and of these the second in the lower jaw were the largest. There were no traces of the third or fourth premolars. It is a general rule amongst mammals that the first premolar has no predecessor, or else, perhaps, that this tooth is really a permanent milk-tooth, the only exception usually given to this rule being in the case of Hyrax**. In reference to the former of these views, it is well known that there is a tendeucy in many mammals towards the suppression of the milk-teeth, as, for instance, in the Rabbit3, this being carried to an extreme in Marsupials, as Prof. Flower has shown4, and (as far as is yet known) in the Guinea-pig, in which animals the last is the only one left. On the other hand, as will be seen later on, the fact that in the Tapir the first milk-molar is considerably larger than its successor might be taken in support of the first view. It is thus interesting to find a more primitive condition in the dentition of animals like the Tapir and Hyrax. A comparison of the dentition of the young with that of older animals is instructive. As in the Horse5 and other Ungulates, the last deciduous molar remains functional for a long while, probably for some time after the animal is fullgrown; and it can be at once distinguished by its worn appearance. The first molar of the Horse appears long before the milk-molars are shed, and, by the time all the permanent teeth have appeared, is considerably worn. Thus an examination of a Tapir's skull in which, though apparently adult, the last milk-tooth had not been shed, might easily mislead one, and give the idea that there were only three premolars above and two below. That "this is not the case is proved by the skull of an American Tapir in the Biological Museum of the Normal School of Science, to which Prof. Huxley has drawn my attention. In this, though apparently a nearly adult animal, the last milk-molars above and below were still functional, and above them, in the sockets, are the teeth which were destined to take their place. Prof. Huxley has also kindly allowed me to make a section of the jaw of an Indian 1 ' Osteographie,' tome iii. 2 Both de Blainville and Owen (Odontography, p. 605) state that in the Tapir the first deciduous molar is succeeded by a permanent one; but some doubt is thrown on this conclusion by Huxley, in his ' Comparative Anatomy of Vertebrated Animals,' p. 365. 3 See footnote on page 655 of Prof. Huxley's article "On the Application of the Laws of Evolution to the Arrangement of the Vertebrata," P. Z. S. 1880. 4 Phil. Trans. 1867. 5 Prof. Owen states (Odontography, p. 581) that in the Horse the last deciduous molar is usually not shed until the last true molar has appeared. |