PROFESSOE OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 



79 



part of the maxillary which supports the lacrymal, which forming that part of the rim 

 of the orbit and extending backward adds to the depth of the depression. The rim sub- 

 sides above the lacrymal, and the upper part of the orbit is continued convexly upon 

 the upper part of the skull parallel with the posterior ends of the nasals and con- 

 tiguous part of the frontal [ih. u). The superorbital ridge is resumed by the outstand- 

 ing and down-bending process of the frontal (Plate II. 12), which, being broken away on 

 both sides of the skull, exposes the large air-sinus with which it was excavated. The 

 rimless upper part of the orbit is 10 lines in extent. The orbit is relatively smaller 

 than in Felis, deeper anteriorly, and more significantly different by its wall not being 

 pierced for the lacrymal canal, the entry of which {ih. 13) is situated externally, as shown 

 in the first-described specimen of Thylacoleo. The length of the nasal bones (Plate IV. 

 fig. 3, 15) is 3 inches 6 lines ; their least breadth, conjointly, is 1 inch ; they slightly 

 expand at both ends, but most so posteriorly, where they are 2 inches across. Their 

 median suture remains ; that of the frontals is in great part obliterated, and the con- 

 joined frontals [ih. n) enter the posterior interspace of the nasals. The fronto-nasal 

 suture is undulatory. The nasal processes of the maxillaries do not extend so far back 

 as the nasals, which terminate angularly, but with the apex largely rounded off. 



The upper cranial surface of the frontals (Plate IV. fig. 3, n) contracts backward to 

 the intertemporal ridge (ib. t); the boundary between frontal and parietal is not shown. 

 At the anterior expanded part of the frontals the external surface forms a pair of low 

 convexities divided by a median longitudinal shallow channel, but deeper and with the 

 convexities better marked than in the first specimen. These convexities give a contour 

 line to the upper part of the skull (Plate II.), resembling that in the Brown Bear, 

 which also the skull resembles in the breadth of the naso-maxillary part. The upper 

 and hinder parts of the cranium correspond with those which were characterized in the 

 former paper. 



The dentition of the upper jaw, as indicated by alveoli in the present specimen, 

 includes, on each side, three incisors (Plate III. ^, 1, 2, 3), followed by three or four 

 other teeth : of these, one is the great carnassial 4), another, the small transversely- 

 oblong tubercular (m 1} : the seat of doubt is between the carnassials and incisors. To 

 one of the doubts expression has been already given ; whether, viz., the carnassial was 

 preceded by one small two-rooted premolar [p 3), or by two smaller and single-rooted 

 teeth. A canine appears to be represented by the tooth with a subcircular, conical, 

 obtusely worn crown, under 3 lines in diameter, supported on a thicker base (ib. c). 

 Future specimens may clear up this part of the dentition of Thylacoleo. It is certain 

 that the anterior incisor (ib. i 1) bore a relation of size to the carnassial similar to that 

 of the canine tusk in Felis to the carnassial. Of the two small premaxillary teeth 

 which succeeded the front tusk, neither is preserved. 



The size of the laniary canine in Felis being here transferred to the first incisor, its 

 function as killer was similarly provided for by its approximation to the moving power, 

 througli the extreme shortness of both upper and lower jaws, especially anterior to the 



