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The mandible of the Tasmanian Wombat lias the singular proportions of being as 

 broad as it is long. In the specimen figured (PI. LIII. fig. 1) the length is 4 inches 

 6 lines. In one jaw of Ph. platyrhinus the length is 6 inches, the breadth 5 inches 

 9 lines. In a second specimen, with a length of 5 inches 9 lines the breadth is 5 inches 

 3 lines. In a Ph. latifrons with a mandible 4 inches 10 lines in length, the extreme 

 breadth is 4 inches 4 lines. In a second specimen the mandible, with a length of 

 5 inches, has a breadth of 4 inches 7 lines (PL LIV. fig. 1). 



The marsupial characteristic of the inflection of the angle of the lower jaw (PI. LVI. 

 figs. 1, 2, 3, a) and the flattening of the lower border or base of the ' ascending ramus,' 

 reaches its maximum of development in the Wombats. The increase of breadth is due 

 to the lower border of the external coronoid or ' crotaphyte ' fossa (Pis. LII., LIV. 

 figs. 1, 2, 3,//), which extends as far outward as the mandibular angle does inward. 

 The coronoid process (ib. c) is comparatively slender ; its base divides the ' crota- 

 phyte ' (f) from the ' angular ' [d, e) fossa. The breadth and depth of these bespeak 

 the force of the masticatory (masseteric and pterygoidean) muscles, as the coronoid pro- 

 cess indicates the comparative weakness of the biting (temporal) muscles). The latter 

 process is usually undermined by a transverse canal or short tunnel between the two 

 fossa?. The exception of its absence I have hitherto noticed in individuals of the hairy- 

 nosed Wombat only, and it is rare in Phascolomys latifrons. 



The postmolar process makes a low angle in the mandible of Phascolomys platyrhinus 

 (PL LIII. fig. 2) and of Phascolomys latifrons (PL LIV. fig. 1). The longitudinal canal 

 (ib. ib. u) between this production of the alveolar border and the base of the coronoid 

 varies somewhat in relative width, a character which aids in the determination of frag- 

 mentary mandibular fossils. 



The subsymphysial foramina (PL LVI., r, ;■) are usually closer together in Phascolomys 

 platyrhinus (fig. 1) than in Phascolomys latifrons (fig. 3). 



Other modifications of the lower jaw in species of Phascolomys will be noted in 

 treating of such fossils in a subsequent section of the present work. 



§ 2. Dental Characters. — The dentition of Phascolomys is unique in the mammalian 

 class; its formula is i% c% p\'\-> w&*-|=24; but the teeth symbolized by shape as 

 " premolar " and " first molar " belong, like the other three molars, to the first set, 

 which, so far as I have observed, is not in any proportion deciduous. On the contrary, 

 every tooth enjoys unceasing growth, is consequently rootless, and is curved in the 

 segment of a circle ; it has also a partial investment of enamel. This is not the case 

 with the molars of any rodent, or of any other marsupial save the Wombats. In the 

 upper molars (PL XLVIII. fig. 3, e, PL XLIX. fig 3, e) the enamel is laid upon the 

 inner, in the lower molars (Pis. LIII. & LIV. fig. 1) on the outer side. It is coated, 

 with the rest of the tooth's surface, by cement. 



The upper incisors in Phascolomys platyrhinus (PL XLVIII. fig. 1, i, figs. 2, 2') are 

 subcompressed, with a narrow subelliptic transverse section (fig. 2'), of which the long 

 axis is directed from before rather outward and backward. Those of Phascolomys lati- 



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