PEOFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTEALIA. 



625 



The base of the masseteric process of the maxillary (Plate XXXV. fig. 1, 21') is a ver- 

 tical outstanding ridge, beginning below about an inch above the fore part of the last 

 molar alveolus, or above the interspace between the last and penultimate sockets, ac- 

 cording to the age of the individual. It becomes thinned as it rises and projects, and 

 then suddenly expands to form the fore part of the zygoma and to send down the pro- 

 cess. This is slightly twisted upon itself outward and backward, concave on the hinder 

 and inner surface, convex at the opposite surface ; the fore part of the vertical base of 

 the zygomatic process of the maxillary is smooth and concave. 



The alveolar border of the maxillary contracts and terminates obtusely behind the last 

 molar (m 3, Plate XXXVIII. fig. 2). It articulates with the palatine, leaving a hinder 

 angular interval into which the lower and fore part of the pterygoid is wedged. The 

 outer part of the concave hind border of the bony palate curves from the pterygoid 

 inward and forward to opposite the mid-division of the last molar : the palatines appear 

 to complete, with the maxillaries, the hind part of the roof of the mouth, without leaving 

 a vacuity. 



Portions of the maxillary and palatine of two other individuals are equally without 

 indications of any wide postpalatal vacuity opposite the interspace between the last and 

 penultimate molars. In advance of this interval the bony palate, due here to the maxil- 

 laries exclusively, extends so as to give a breadth of the palate between the penultimate 

 molars of 4^ inches. 



Anterior to the masseteric process the outer alveolar wall of the maxillary is undulated 

 by the vertical prominences, indicative of the large and thick roots of the molar teeth. 

 The alveolar border contracts as the teeth advance in position and decrease in size, and 

 becomes a ridge anterior to the first molar in place (usually the second of the series (d *) 

 in full-sized Biprotodons). This antalveolar or diastemal ridge (Plate XXXV. fig. 1, x) 

 curves upward and inward, approaching its fellow, then arches downward and terminates 

 at the back part of the socket of the third incisor, where the maxillo-premaxillary suture 

 begins. At the wider hind part of the interval, between the antalveolar ridges, there 

 seems to have opened an anterior or prepalatal canal leading to the fore part of the nasal 

 cavity, the orifice being elongate. In advance of this the deep and narrow channel 

 between the fore part of the diastemata is entire. Above these ridges, the outer plates 

 of the maxillaries swell outward as they ascend to form the lateral walls of the antorbital 

 part of the nasal chamber, arching inward again above to join the nasal bones (15). 



The maxillo-nasal suture seems to have a relatively greater extent than in Phascolomys ; 

 but owing to the short facial or antorbital part of the skull, as compared with Macropus, 

 it is of much less relative extent than in that genus. The antorbital foramen (ib. figs. 

 1 & 2, 21) is longest vertically. 



Each premaxillary (Plate XXXV. figs. 1 & 2, 22) is deeply excavated by three alveoli, 

 the foremost the longest, largest, and most curved. The inner walls of these alveoli 

 rise as a strong vertical crest (22') dividing the lower part of the nasal outlet. The inci- 

 sive alveoli succeed each other from before backward ; and, owing to its superior size. 



