OCR Text |
Show 1900.] STRUCTURE OF THE MUSK-OX. 711 primitive type. It is consequently impossible to derive Ovibos from the Sheep on account of this. In the young summer calf the three milk-premolars of the upper jaw are developed, and the first molar is just protruding from the socket. The middle and three hindmost premolars are bilobed, and on the latter can be seen, between tbe two lobes on the inner side, a small, but distinct, ridge representing the accessory column. In the same calf the three mandibular milk-premolars are developed and the first molar just protruding. The foremost deciduous premolar is small and simple, the middle is two-lobed, and the hindmost is three-lobed. In the domestic calf there are on the outer side of this hindmost mandibular milk-premolar two well developed, Fig. 10. Section through a milk-incisor of a calf of Bos taunts. although shorter, additional folds. These are not entirely absent in the Musk-calf, but only developed as two short tubercles in a corresponding situation at the base of the tooth. From Bichardson's description (I. c. p. 71) it becomes evident that the deciduous molars are retained at least a year. The permanent premolars of the Musk-ox are one-lobed; and the molars are two-lobed except the third mandibular molar, which is three-lobed, as is already recorded by previous authors. As Boyd Dawkins says (I. c. p. 8), the upper true molars of the Musk-ox "are differentiated from those of Bison and Buffalo by the |