OCR Text |
Show 1900.] STRUCTURE OF THE MUSK-OX. 709 pointed out the parallel development in this direction in the Beinr deer (I. c. p. 12). The anterior part of the mandible of the Musk-ox gets, through the already mentioned excavation for the canalis inframaxillaris and because the same is extended much forwards, a very constricted or compressed appearance which is rather striking (fig. 8). A result of this shape of the sjmiphysis is, of course, that the incisors become more vertical than in other ruminants, and are therefore worn off straight (fig. 8, o*), not obliquely as in other forms. The incisors of the Musk-ox cannot accordingly retain the anterior cutting-edge as the obliquely placed and obliquely worn teeth can, but in old animals the worn crown of the incisors presents a round surface placed at a right angle to the longitudinal axis of the nearly cylindrical tooth. But even the unworn incisors of Ovibos have quite another shape to those of other Cavicornia. Mandibles of male and female Musk-ox. The crowns of the incisors are very small, comparatively thick, and less spatulate than those of other forms \ I am therefore inclined to think that the incisors of the Musk-ox-not being so much used because the strong lips act as substitutes for them in their function of seizing the food-are becoming gradually reduced. The crowns of the incisors of tbe Musk-ox are, however, evenly capped with enamel, and this can be said not only of the permanent, but also of the milk-dentition. The milk-incisors of the Musk-calf 1 In the Gazelles aud some others it is only the two median incisors which have been strongly developed and very broadly spatulate, the lateral ones being very narrow. The latter have, however, retained their cutting-edges aud are worn obliquely, so that their function is the same although their breadth has been reduced |