Mui'Uke from Central Australia. 119 



by leaps like a kangaroo or jerboa ; while similar comparisons in 

 the case of Coiiilurus equally convince me that these advanced in 

 the more usual manner. 



In addition to the peculiarities already mentioned, the foot is 

 very narrow, and the first and fifth digits are set back, so that 

 instead of the first digit reaching almost to the front of the 

 anterior pads, and the fifth far beyond tliem, as in Mus decumanus 

 they altogether fail to approach them or barely reach their 

 posterior edge respectively. 



The various characters here sketched suggest a tempting field 

 of speculation on the evolution of the foot, which however will l)e 

 here, merely indicated. The practice of jumping, necessarily 

 throws the area of contact with the ground very far forward ; the 

 first and fifth digit are unnecessary for such progression, as 

 abundantly pi'oved by the consideration of other forms, such as 

 Alactaga, Euchoretes and Plaiycercomys. These digits become 

 reduced to mere vestiges, indicating a former function and finally 

 disappear as in Dipus. That such a condition is taking place in 

 Podaiiomalus is suggested Ijy the recedence and shortening of 

 these digits, and more especially by the absence of their pads, 

 which, being tegumentary structures, would naturally become 

 lost long before the bones themselves suffered material diminu- 

 tion. 



The phraseology used is strictly conventional ; the same appear- 

 ance would be produced by the advance of the median digits as by 

 the retreat of the external ones. It is extremely probable that 

 both factors are operative in bringing about the result. 



Tail-scales average twelve to the centimetre. Mamma?, 0'2 = \. 

 Palate ridges, three predental and six interdental. 



Skull. 8tout, smooth, facial portion rather produced, preorbital 

 processes well developed : l»ulla? large, the portion above the 

 meatus projects considera))ly and can be seen when viewed fi'oin 

 above : front edge of antei'ior zygoma root evenly concave, the 

 upper portion pi-qjects and forms a sharp angle. The inter- 

 parietal is very narrow, being only half the width of the brain-case: 

 coronoid low, not projecting above a line drawn from the tip of 

 the incisor to the top of the condyle ; the angle is deflected 

 outwards and deeply excavated to receive the masseter : foramen 

 magnuni much higher than wide. 



