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Show 182 PROF. W. H. FLOWER ON THE MUSK-DEER. [Mar. 16, the Cervida by the absence of canine teeth, by the absence of distinct metacarpals and phalanges to the outer (second and fifth) digits, by the presence of a gall-bladder, by the single lachrymal canal placed within the margin of the orbit, and by the presence of Cowper's glands. But yet, as will be shown presently, it is doubtful if any one of these characters is exclusively characteristic-that is, may not be found in some member of the other groups. There is still another character of some importance, derived from the form of the molar teeth. Although there is nothing in the general mode of arrangement of the enamel-folds or in the accessory columns absolutely distinctive between the two groups, existing species can generally be distinguished, inasmuch as the Deer are what may be termed " brachyodont," and the Bovida " hypso-dont"*: i.e. the teeth of the former have comparatively short crowns, which, as in most mammals, take their place at once with the neck (or point where the crown and root join) on a level with or a little above the alveolar border, and remain in this position throughout the animal's life; whereas in the other form (the crown being lengthened and the root small) the neck does not come up to the alveolar level until a considerable part of the surface has worn away, and the crown of the tooth thus appears for the greater part of the animal's life partially buried in the socket, and no part of the root is visible. In this form of tooth (which is always most developed in the posterior molars of the permanent series) the constituent columns of the crown are necessarily nearly parallel, whereas in the other they diverge from the neck towards the free or grinding surface of the tooth. In the more completely hypsodont forms, the interstices of the lengthened columnar folds of enamel and dentine are filled up with cementum, which gives stability to the whole organ, and which is entirely or nearly wanting in the short crowned teeth. The same modifications from low to high crowns without essential alteration of pattern is seen in an even still more marked manner in some of the Perissodactyle Ungulates, where the tooth of a horse bears to that of Anchitherium the same relation that that of an ox does to the early Selenodont Artiodactyles. As the hypsodont tooth is essentially a modification of, and, as it were, an improvement upon, or specialization of, the other, it is but natural to expect that all intermediate forms may be met with ; and it is not always easy to decide, especially in old and much-worn teeth, in which group any given example should be classed. Even among the Deer themselves, as Lartet has observed**)*, the most ancient have very short molars, and the depressions on the grinding-surface are so shallow that the bottom is always visible, while in the Cervida of the more recent Tertiary periods, and especially the Pleistocene and living species, these same cavities are so deep that, whatever be the state of the dentition, the bottom cannot be seenj. * Terms first used, I believe, by Mr. Boyd Dawkins. t Comptes Rendus, 1868, t. lxvi. p. 1119. | Some existing Deer, as the Axis, are far more hypsodont than the majority of the family; and, on the other hand, many of the Antelopes are far more brachyodont than the more typical Bovida-Goats, Sheep, and Oxen. |