1900.] 



STRUCTURE OF THE MUSK-OX. 



709 



pointed out the parallel development in this direction in the Rein- 

 deer (I. c. p. 12). The anterior part of the mandible of the Musk- 

 ox gets, through the already mentioned excavation for the cunalis 

 inframaxillaris aud 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 symphysis is, of 

 course, that the incisors become more vertical than in other 

 ruminants, and are therefore worn off straight (fig. 8, <$ ), 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. 



Fig. 8. 



5 



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 the 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 and 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 

 and are worn obliquely, so that their function is the same although their breadth 

 has been reduced. 



