PEOFESSOE OWEN ON THE FOSSIL MAM3IALS OF ATJSTEALIA. 77 



goid. This extension (ib. so), flat below, convex above, contracts to a diameter of eight 

 lines opposite the middle of the posterior nostril, then increases in breadth, and loses in 

 depth as it passes into the pterygoid wall of the wide and deep pterygo-sphenoid basi- 

 cranial longitudinal median canal. Each posterior bony nostril is longitudinally ovate, 

 with the great end forward, 2 inches in longitudinal and rather more than 1 inch in 

 transverse diameter ; with the plane of the opening inclined from without upward and 

 inward, and, more feebly, from before upward and backward. The bony roof of the mouth 

 is thus much reduced in length ; a dimension which is surpassed by its breadth between 

 the great camassial teeth. Its posterior border is thin, and sharp where it forms the 

 fore part of the palatal nostril, and gradually thickens, becoming smoothly convex at the 

 outer side of that aperture. The bony palate is perforated by a pair of apertures about 

 1 inch in advance of the hind border, and 1^ inch from the anterior end ; that on the 

 left side (Plate III. a) is elliptic, about 5 lines by 3 lines in its two diameters ; on the 

 right side the bony palate is partly broken away : these answer to the incisive or pre- 

 palatal foramina, and are on the line of the suture of the premaxillary with the max- 

 illary palatal processes. The breadth of the palate, which is nearly 4 inches between 

 the hind ends of the camassials, is reduced to 1 inch 3 lines anterior to the small open- 

 ings above-mentioned, and rapidly contracts to a breadth of 3 lines [between the large 

 sockets of the anterior teeth, which here, descending, convert the fore part of the palate 

 into a deep groove. 



The most welcome and instructive part of the present fossil skull is the fore part, 

 giving evidence of the anterior teeth, and of the formation, position, and aspect of the 

 external nostril. This orifice (Plate IV. fig. 1) is formed by the premaxillaries (22) and 

 extremities of the nasals (15). A characteristic of most of the facial sutures in Thylacoleo 

 is their finely undulated or subdentate structure. This is shown between the maxillary 

 (Plate II. 21) and malar (26), between the maxillary (21) and premaxillary (22), and between 

 the nasals (15) and premaxillaries ; though not in the median suture between the nasals 

 themselves. These bones (Plates II. & lY. figs. 1 & 3, 15) slightly expand at their fore 

 ends, where their free margin is thick and obtuse, and forms the upper third of the ex- 

 ternal nostril. The premaxillaries form the sides of the opening by a similar margin, 

 which rapidly expands at the lower half, to form or be continued, sloping fonvard, into 

 the alveoli of the pair of incisor tusks [i 1). The inner or medial border of each alveolar 

 outlet (Plate III. i 1) is continued downward below the level of the contiguous bony 

 palate for about 4 lines, forming the sides of a groove or canal at that part about 3 lines 

 in breadth, which expands as the palate extends backward between these alveoli. At the 

 middle of the lower boundary of the external nostril the premaxillaries rise into a slight 

 prominence ; the lateral borders of the nostril are slightly concave vertically (Plate 

 II. 22); the forai of the nostril (Plate IV. fig. 1) is transversely elliptic; its plane almost 

 vertical, with the lower border a little advanced ; the anterior margin of the nasals is, 

 through fracture, not quite entire. The vertical diameter of the nostril is 1 inch 2 lines, 

 the transverse diameter 1 inch 10 lines. The vertical extent of the premaxillary is 



