304 PROF. OWEN ON THE OSTEOLOGY OF THE MARSUPIALIA. 



wards : this surface is feebly striated longitudinally : the opposite or concave surface 

 is impressed by a shallow longitudinal groove. The entire incisor is more curved than 

 that of the Phascolomys Vombatus ; i. e. it describes the larger segment (nearly one half) 

 of a smaller circle (fig. 6, b). In Phase. Vombatus the outer or enamelled surface of the 

 upper incisor is indented by a shallow longitudinal groove, as well as the opposite side, 

 which is the most convex transversely (see the transverse section, fig. 3, o). The entire 

 incisor describes about one-fourth of a larger circle (fig. 3, b). The lower incisors 

 are narrower in Phase, latifrons, and trihedral (fig. 7, c) ; the enamelled anterior or 

 under surface is flat; the outer surface longitudinally impressed, and almost devoid of 

 enamel. In Phase. Vombatus the lower incisors are also trihedral, but the outer surface 

 is convex and enamelled ; the entire teeth, and the symphysis of the jaw supporting 

 them, are relatively larger (fig. 3, c). The first lower molar (premolar) is relatively 

 larger, the last relatively smaller in Phase, latifrons. 



In this species the intermaxillary part of the skull is higher in proportion to its width, 

 less convex externally (compare figg. 2 & 5). The nasal bones are relatively broader, 

 forming the whole upper surface of the anterior third of the skull in Phase, latifrons 

 (compare figg. 4 & 1). The inter-orbital part of the skull is relatively much broader in 

 Phase, latifrons, and is produced on each side into a well-marked supra-orbital ridge 

 and post-orbital process (fig. 4, o), both of which are almost obsolete in Phase. Vombatus 

 (fig. 1, o). The temporal fossae are not bounded, as in Phase. Vombatus, by two nearly 

 parallel and remote longitudinal ridges, but are continued by a convex, rather irregular 

 tract, to near the middle of the upper region of the cranium. 



A very remarkable feature in the skull of the Phase, latifrons is the supra-tympanic 

 cell (fig. 5, t) excavated beneath the base of the zygoma : this cell in Phase. Vombatus 

 (fig. 2, t) is transversely oblong, simple, one inch by half an inch in size ; in Phase, 

 latifrons it extends inwards one inch and a quarter, and expands to an antero-posterior 

 diameter of one inch and a half, and a vertical diameter of one inch, having an oblong 

 outlet nearly one inch in length and half an inch in depth, slightly contracted in the 

 middle. This difference in the size of the supra-tympanic cell is obviously not the 

 eff"ect of age, as the skull of the Phase. Vombatus compared is that of an old animal with 

 strong temporal ridges. 



In Phase, latifrons the articular surface for the condyle of the lower jaw is broader 

 and less convex ; the anterior boundary of the zygomatic space is less angular ; the 

 palatal surface of the intermaxillaries is deeper ; the curve of the lower border of the 

 lower jaw is much deeper ; the coronoid process (ib. cr) is higher and narrower, and the 

 post-symphysial depression is almost obsolete. 



Figures 1 and 4 show the characteristic differences in the upper surface of the skull 

 of the two species, and figures 2 and 5 those observable on a side view, in which the 

 curvature of the lower jaw of Phase, latifrons (fig. 5) is a conspicuous character. 

 Figures 3 and 6 show the difference in the form of the anterior bony aperture of the 



