OCR Text |
Show 110 MR. W. BATESON ON [Feb. 2, series is relatively a small tooth, as, for example, nT3 or m2 in the Dog, then in cases of an addition to the series by which this terminal tooth becomes the penultimate it will be found that this penultimate tooth is larger and better developed than the corresponding ultimate tooth of a normal animal of the same size. Of this phenomenon two examples must here suffice. The first is a skull of Canis azarce in the Leyden Museum (fig. 31, p. 109). In this figure, I and II represent the back-teeth of this abnormal specimen, I being the upper, and II the lower jaw. By the side of these are shown the upper and lower jaws of a normal specimen of rather larger absolute size. In the upper jaw there is a supernumerary m 3 on both sides and the great enlargement in m 1 and especially in m 2 is very striking. In the lower jaw there is no extra tooth, but the molars are considerably larger than the normal size. The next case is that of Dasyurus maculatus, having an extra Dasyurus maculatus. A. Right upper jaw of a normal specimen. B and C. Upper and lower jaws of an abnormal specimen having an extra molar in each lower jaw and in the left upper jaw. In correlation with this change the sixth upper back-tooth (m3) has been increased in size. (The abnormal specimen was of less than normal size.) From specimens in the British Museum. molar in the left upper and both lower jaws. In this case, owing to the great difference which normally exists both in shape and size between the last tooth and the last but one, some obscurity is introduced by the changes associated with the presence of an extra tooth and it would be difficult to determine the nature of the upper teeth if this phenomenon of Variation were unrecognized. The structures are shown in fig. 4, A being the right upper jaw of a normal specimen, while B and C are the jaws of the abnormal form (Brit Mus. 983 b). The normal specimen is unfortunately much larger 1 This drawing was kindly made for m e by Mr. J. J. Lister. |