118 Proceedings of the Royal Society of Victoria. 



The hind feet, which present the greatest peculiarity of the 

 animal, are remarkable for their length and for the small number 

 of the pads. In order to fully appreciate the peculiarity, the feet 

 of Mus decumamis may be first examined. This species is much 

 more suitable for a type than Mi/s raitus^ (sometimes adopted), 

 because it is everywhere procurable, whereas the latter species is 

 not only troublesome to obtain, but its identification may present 

 subject for controver.sy. 



3. INTERDIGITAL. 

 4 INTERDIGITAL. 



OUTER METATARSAL 



2. INTERDIGITAu 



1 INTERDIGITAL 



INNER METATARSAL. 



Right hind foot of Brown Rat (Mus dectimanus), showing number 

 and position of foot pads. (Natiiral size). 



The sole of the foot of the Brown Rat is furnished with six 

 pads, one at the base of each interdigital fissure, (the first, second, 

 third and fourth interdigitals), the fifth, posterior to the pad at 

 the base of the outer digit (outer metatarsal), and the sixth 

 on the inner side, nearest to the heel (inner metatarsal). This 

 last pad is narrow and long, but in some sjDecies it is quite 

 small and roundish, and as it is a valuable factor, its relative 

 size and distance from the heel is made use of for descriptive 

 purposes. 



Turning now to the foot of Podanonialus longicaudaius 

 (fig. 2.e.) it will be observed that of the usual six pads, two 

 or more are absent. The metatarsals are quite obsolete, and 

 it is only in certain examples that the first interdigital may 

 be traced. 



A comparative study of the pads, the toes, and of the greatly 

 lengthened limb, shows very conclusively that the rat i^rogresses 



