445 



The dentine is exposed on the fore lobe of the last molar, and the fore part of the 

 enamel-ridge of the hind lobe is nearly worn through ; the prebasal ridge (f) also shows 

 abrasion. A hollow transverse field of dentine is exposed on both lobes of the penul- 

 timate molar. With these indications of greater age, the maxillary pier (21') has retro- 

 graded, and projects on the transverse parallel chiefly of the last, instead of the penul- 

 timate, molar, as in the younger specimens (Plates LXXXVII. & CVHL). In all the 

 bony palate is entire. 



The fore part of the present skull has been broken away in front of the premolars, 

 and shows a diastema 2 inches in extent From the back of the socket of the third 

 incisor to the fore part of the crown of the first is 1 inch 3 lines. Of the third incisor 

 (the seat of variety in existing Kangaroos), the left is lost, and of the right one only the 

 fang remains. The crown of the second right incisor is worn nearly to its base. The 

 first or front incisor (Plate CIX. fig. 6) is present in both premaxillaries, with its fang 

 exposed in the left one. The crown is worn to the level of the palate (ib. fig. 4, i 1) ; 

 the smooth and polished surface presents an oval figure, the great and outward ; the 

 long dameter is 7-^ lines (15 millims.); the short diameter, near the outer side of the 

 worn surface, is 5-^- lines (11 millims.). The enamel, nearly 2 millims. in thickness, is 

 limited to the anterior surface, bending slightly back at the outer and inner margins ; 

 not more than 9 lines length of the enamelled crown remains. The whole incisor, as 

 usual, is curved lengthwise, with the greater convexity anterior ; the root contracts to 

 its implanted end ; the length of the incisor, in a straight line, as here worn, is 1 inch 

 8 lines. The portion of cranium preserved, from the fore part of the front incisor to 

 the back of the last molar, measures 6 inches 8 lines. According to the proportions of 

 some existing Wallabies, which retain the premolar with the last molar in use, 5 inches 

 may be added for the extent of skull behind the last molar, and the total length of the 

 skull in Sthenurus Brehus may be moderately estimated at 12 inches (as in the restora- 

 tion, Plate CVIII.). 



About 2 inches of the facial part of the premaxillaries are preserved, bounding by a 

 curved and obtuse border, thinning as it rises, the anterior nostril (Plate CVIII. fig. 1, 22). 



The skull, so far as it is shown in the present specimen, has been crushed sideways, 

 not partially, as in the cave-fossil, but by a pressure operating through a more extensive 

 plane, and which I deem to be due to movement of the matrix, rather than to the jaws 

 of a destroyer or devourer. 



The lower jaw, which appears to have been imbedded originally in connexion with 

 the upper one, has suffered similar lateral compression. Only the fore part of the 

 mandible has been obtained or transmitted ; it includes the pair of lower incisors, with 

 the premolar and two following molars of the right side (Plate CIX. figs. 7 & 8) ; these 

 are much worn. The length of the diastema is 2 inches ; in Sthenurus Atlas (Plate 

 LXXXII. fig. 5) it is 1 inch 3 lines. In the course of the pressure to which this man- 

 dible of Sthenurus Brehus has been subject, the attachment of the broad symphysis has 

 been overcome, and the right ramus has been moved a little in advance of the left (ib.fig. 7). 



46* 



