526 



PEOFESSOE OWEN ON THE FOSSIL MAMMALS OF AUSTEALIA. 



the outer border of the first projects further from the midline than does that of the last. 

 Viewed from the palatal aspect the two series of incisive alveoli converge backward, 

 instead of forward as in the Kangaroo and most other quadrupeds. The malar bone 

 (Plate XXXV. fig. 1, 26) ascends from its junction with the maxillary to join the lacrymal 

 (73) at the fore part of the orbit, by a very narrow curved strip or process ; its main body 

 is suspended in the zygomatic arch, of which it constitutes the anterior half, and the 

 lower part, as far as, and including, the " eminentia articularis." The suture between 

 the squamosal and malar elements of the zygoma is almost straight, extending from 

 behind the orbit obliquely backward and downward to the glenoid cavity, of which 

 articular surface the malar " eminentia," here more flattened than usual, contributes the 

 fore part. This articulation (ib. fig. 4) is most extended transversely to the skull's axis ; 

 its hinder half (ib. ib. 27) is concave from before backward, its fore part (ib. ib. 26) 

 convex, but becomes flattened or a little hollowed on the " eminentia." 



The lacrymal (ib. fig. 1, 73) is perforated by the canal, marsupial-wise, in advance of 

 and external to the orbital cavity. 



§ 3, Mandible. — A transversely extended subconvex condyle (Plate XLII. figs. 3 & 4) 

 adapts itself to the cavity off'ered by the base of the zygoma. The condyle is 5^ inches 

 in transverse extent, 1 inch 9 lines from before backward ; it is, in that direction, most 

 convex. The condyloid process is supported by a three-sided neck quickly contracting 

 to 1 inch 9 lines in transverse diameter (ib. fig. 3, ; it is broadest and flattened behind, 

 contracted in front to the ridge-like beginning of the " coronoid " plate (ib. figs, 2 & 4, r), 

 which extends forward near the outer side of the neck. The condyle is more extended 

 inward (ib. fig. 4, c) than outward (ib. ib. c') of this advancing vertical coronoid plate. 

 The flat surface at the back part of the neck is continued into a suddenly expanded 

 hinder facet of the ascending ramus, formed by the outward production of the hind 

 wall or boundary of the outer depression for the insertion of the temporal muscle, and 

 by the inward production (Plate XXXV. fig. 3, e) of the hind wall or boundary of the 

 deep inner concavity of the ascending ramus, where opens the large entry (Plate XLII. 

 fig. 2, 0) of the dental canal. Below this orifice the concavity extends downward through 

 the concomitant extension of the inner plate or hind wall to the lower border of the 

 horizontal ramus, where it gradually subsides. The hind wall of the outer depression 

 of the ascending ramus (Plate XXXV. fig. 1, e) follows the contour of that of the inner 

 depression, but sooner subsides; the interspace is a continuation of the broad hind 

 flattened facet which, as it descends, gets a more outward aspect. Beyond the sub- 

 sidence of the outer plate it gives the appearance of a bending inward of the angle of 

 the jaw (ib. fig. 2, e'), and that to a degree which is characteristic of Marsupials. The 

 outer or crotaphyte depression of the ascending ramus (Plate XXXV. fig. 1,/) gradually 

 gains the ordinary level of the outer surface of the horizontal ramus, and does not 

 undermine the ascending branch to communicate with the inner concavity as in Macro- 

 pu.s. In the shape of the condyle Dijirotodon resembles Phascolomys, in which the 

 intercommunicating canal is much reduced. 



