198 



ably large proportion of the symphysis in Diprotodon to the size of its molar teeth there 

 are no quadrupeds which so nearly resemble it as the Notothere and the Wombat; but 

 iu this existing Marsupial the symphysial part of the jaw is broader in proportion to its 

 depth. The long and narrow symphysial junction in the Kangaroo is peculiar for the 

 yielding movements allowed to the rami upon each other, which is betrayed by those 

 of the long procumbent depressed incisors in the living animal*. 



§4. Dentition. — The dental formula of Diprotodon is: — cjj=j!, mj£|=28. Of 

 the upper incisors the first or anterior pair .(Plate XIX. figs. 1 & 2, i 1 ; Plate 

 XX. figs. 1- 0) are large curved scalpriform teeth, of which I have not found indi- 

 cations of cessation of growth in any specimen. The skull above described and figured 

 (Plate XIX.) has been that of an aged male, judging from the size and degree of attri- 

 tion of the teeth which are retained ; but the anterior incisors above, like the pair below, 

 are continued to the bottom of their deep alveoli without contraction, and with the re- 

 tention of a widely open pulp-cavity (Plate XX. fig. 6). It is obvious that these 

 strong anterior incisors (ib. figs. 1-4) worked with the evergrowing power of the " dentes 

 scalprarii" of the Wombat, the Aye-aye, and the Rodents. 



In the above skull the length of il, following the convex curve of the tooth, is 11 

 inches ; its circumference is 4 inches 9 lines ; the breadth of the oblique abraded 

 working surface is 1 inch 9 lines ; the longitudinal extent of that surface is 2 inches ; 

 but this varies in other specimens. An extent of 8^ inches (following the outer curve 

 of the tooth) is lodged in the socket of the premaxillary. 



I made a transverse section of a fragment of the skull of a Diprotodon, including the 

 fore part of the premaxillaries and their scalpriform teeth (Plate XX. fig. 5). Such 

 section of the tooth (i 1, c, d, e) is irregularly three-sided, with the angles broadly rounded 

 off. The inner side, or that next the fellow tooth, is the narrowest ; the front or ena- 

 melled side is the broadest : this side is traversed lengthwise by a wide and shallow mid 

 channel ; the opposite side is grooved by a narrower and rather deeper channel, running 

 along its outer half ; and the inner more prominent half of this side (the concave one 

 lengthwise) also shows a narrow and feeble impression near the mid-line of the tooth, and 

 a broader more shallow impression nearer the angle, dividing the hinder from the inner 

 mu face. This surface, 1 inch 3 lines across (ib. fig. 2), is generally somewhat convex, 

 but wavy through two or three low obtuse longitudinal ridges, with intervening shallow 

 channels. A fossil fragment of a similarly sized tooth yielding such transverse section 

 a.s that shown by this remarkable scalpriform incisor would, according to present expe- 

 rience, determine the genus of Mammal to which it had belonged. 



The enamel coating the anterior convex curve of the tooth is continued over the major 

 part of the outer rounded surface, terminating abruptly along a line (ib. fig. 5, d) 

 external to the outer longitudinal ridge (c) of the posterior surface. In like manner 

 the enamel is continued over the rounded angle between the anterior and inner or me- 

 dial sides of the incisor, and terminates abruptly at e, fig. 5, after covering about one- 

 * First noticed by Mason Good, ' Book of Nature,' vol. i. p. 283. 



