28 



MICROTIN^ 



confined to Madagascar, we find cheek-teeth which, although very- 

 different from those now characteristic of voles, present an arrange- 

 ment of the crown tubercles similar to that which, in a less reduced 

 condition, probably characterized the molars of the ancestor of the 

 Microtinse. In one genus of this Malagasy group, Brachytarsomys, 

 which has adopted a fossorial vole-like mode of living, the molars, 

 although low-crowned and rooted, have been simplified trans- 

 versely in such a way that they show all the broader features 



Fig. 16. — Myospalax fonlanus Thomas. 

 Skull of adult, ventral view, enlarged. 



observable in the cheek-teeth of voles. It is of great interest 

 to observe that in this genus (and in this genus alone) the jaw 

 muscles have developed exactly as in the highest voles; and 

 the skull of Brachytarsomys, although very primitive in many 

 respects, yet makes an undeniable approach towards that of the 

 Microtinse in all those features which in voles depend upon the 

 special development of the anterior part of the temporalis and upon 

 the peculiarities in the arrangement of the masseter lateralis 

 muscles. The parallel, indeed, is so close that it may be necessary 

 later on to transfer Brachytarsomys to the Microtinse. The facts 



