8 PROF. OWEN ON A MANDIBLE AND 



These indications of a distinct species are supplemented by characters of the man- 

 dible itself. 



In PaJorchestes azael ' the inner plate of the ramus descends from the alveolar margin 

 of m 1 and m 2 with a very feeble convexity, soon changing to as slight a concavity, 

 until this is lost in the beginning of the convex sweep round the lower border of the 

 ramus. The initial convexity from the inner border of the alveolus of m 3 in P. azael 

 is but little augmented, and soon passes into a rather deeper concavity, closed by the 

 beginning of the inflection of the angular part of the ramus. A tendency to a smooth 

 flatness characterizes all the inner plate of the ramus descending from the molar alveoli 

 to the lower vertical convexity. 



In Palorchestes crassus the inner wall of the ramus below in 1 describes a moderate 

 but uninterrupted convexity as it descends to the lower border ; and this convexity 

 increases below m 2 and ni 3 before changing to the concavity (flg. 2, a) indicative of 

 the characteristic marsupial inflection of the hinder third of the lower border of the 

 ramus. 



The depth of the ramus below the fore part of »t I in P. crassus is 2 inches 10 lines, 

 that behind m 3 is 3 inches ; the corresponding admeasurements in P. azael are 

 3 inches 2 lines, and 2 inches 7 lines. The depth, or vertical extent, of the ramus 

 augments as the jaw extends forward along the molar series, in P. azael (op. cit. Plate 

 cvi. fig. I), but diminishes in P. crassus (PI. II. figs. 1 & 2) ; and this diminution seems to 

 have been greater below d 4, instead of the increase of depth there shown in P. azael. 



The tooth d 4, in P. azael, is broken away in P. crassus ; but the extent of its 

 alveolus is traceable. A vertical line dropped from its fore part crosses the hind part 

 of the symphysis mandibuli (PI. II. fig. 2, .s), but does not reach so far in P. azael. In 

 this species the symphysis begins in advance of such line. 



A greater proportion of the symphysial part of the mandible and of tlie right ramus 

 is preserved in the subject of the present paper than in that of P. azael'. The sym- 

 physial joint (PI. II. fig. 3) is obliterated by confluence there of both rami, a con- 

 dition I have not noted in any other Macropodal genus. Some approach thereto is 

 shown in a fossil mandible oi the largest species of Procojitodon. In that, e. y., of 

 P. goliah, described in the before-cited work ', I note : — " The symphysis is continued, 

 broadly, to the incisive outlets ; it has assured, apparently, an attachment to each 

 other of the rami of this instructive mandible, too intimate to be disturbed b^" 

 posthumous movements, although ankylosis has not been completed, if it had 

 commenced." 



In the present mandible of a still larger Kangaroo that ankylosis is as complete as 



' Eesearches on the Fossil Remains of the Extinet Mammnls of Australia, 4to, vol. i. (1877) p. 46.5, 

 pis. cv.-c\ii. 



" Op. cit. vol. ii. pi. cvi. fig. 1. ^ Researches ou Foss. Jlamm. Australia, rol. i. (1877) p. 464. 



