312 



EODENTIA. 



tlie under surface of tlie skull, instead of merely seeing the posterior end of the 

 presphenoid and the foramen lacerum orUtale on each side of it, the presphenoid 

 is seen not to he thrown so far forwards as in such mice as M. urbanns and M. 

 hmmirus, and anterior to the foramen lacerum orUtale a spicule of hone is distinctly 

 ohservahle on each side of the presphenoid, passing outwards and expanding in the 

 orhit as the orbital plate of the sphenoid, and anterior to each of these fine osseous 

 rods the optic foramina are clearly visible. 



The infraorbital foramen does not form an incision in the anterior margin of 

 the maxillary root of the zygoma, as in Mus generally. 



The pterygoid fossa is very shallow, and formed chiefly by the palatines, and its 

 base or floor is flattened and expanded as in 31. liomurus and M. tirbanus, but, 

 unUke these mice, is marked by a number of imperfections of ossification. It is 

 very shallow compared with what it is in such bm-rowing rats as Nesokia and 

 the so-called bandicoot M. giganteus, in which it is very deep and perforated 

 at its base. The inner walls of the pterygoid fossa are entire, which is also the case 

 in the small mice already mentioned, whereas in these larger species just named there 

 are generally one or more large imperfections on the inner wall. 



With regard to the number of species, Hodgson indicated another in addition 

 to M. ( V.) oleraceits, but the following table does not reveal any marked distinction 

 between two Nepal specimens and examples from Central India, Charapunji, Burma, 

 and Western Yunnan ; any difi'erences that do occur are probably due to individual 

 variation, or to the diversity in the physical conditions of the localities from whence 

 the animals come. I am therefore disposed to recognize only one species. It will 

 be observed that the upper dental line is the same in all. 



I would also direct particular attention to the proportions which the tail holds 

 to the body in the young animal, as it only slightly exceeds the length of the trunk, 

 while in the adult it is nearly half as long again as the body and head. From this it 

 is evident that the rapidity of the growth of the tail must be considerable, and this 

 probably conduces to that variation in the length of the tail which is so observable 

 m adult individuals of the same species. This would seem to be the case in the 

 long-tailed rat which usually goes under the name of M. rtifescens, in which the 

 proportion of the tail to the body in the young and adult animals is much the same 

 as in M. ( V.) oleraceus. 



Measurements of Mus ( V.) oleraceus, Bennett. 



