﻿76 ALLEN'S NATURALISTS LIBRARY. 



definition of the two is by no means easy. The following are, 

 however, the distinctive characters which serve to differentiate 

 the members of the present family as a whole from those of 

 the MacropodidcB : — 



All the feet with five toes ; those of the fore limbs generally 

 sub-equal ; those of the hind limbs, with the second and third 

 united in a common integument (syndactylous), the fourth the 

 longest of the series ; the fifth but little smaller, and the first 

 (or hallux) large, furnished with a broad clawless terminal pad, 

 and widely opposable to the others (see fig. 3, p. 12). Tail 

 (except in Phascolarctus^ where it is rudimental), long, and 

 nearly always prehensile. Stomach simple ; intestine, except in 

 Tarsipes^ furnished with a blind appendage or caecum ; and 

 the pouch well-developed, with its aperture directed backwards. 

 In the skull the lower jaw lacks the large pocket-like cavity on 

 the outer side of the hinder part, and communicating with the 

 canal of the dental nerve, which forms so characteristic a feature 

 in the Macropodidce. Owing to the frequent presence of a 

 variable number of functionless minute teeth in the anterior 

 part of the jaws, the dentition as a whole is too variable to admit 

 of precise formulation. There are, however, generally three pairs 

 of upper and one pair of functional lower incisors ; the latter 

 wanting the scissor-like action characterising the Macropodidce. 

 Of the two or three premolars usually present, the last is 

 generally furnished with a sharp cutting edge (although this 

 character is less marked than in the preceding family), and is 

 placed obliquely to the hne of the molars. The molars, 

 generally four in number, may be crowned either with blunt 

 tubercles or with sharp-cutting crests. 



It will be obvious that almost the only characters which 

 separate the Fhalangeridce from the Musk-Kangaroo are the 

 structure of the lower jaw and the backward direction of the 

 aperture of the pouch. 



