PROFESSOR OWEN ON TEETH OE A LARGE EXTINCT GENUS. 
247 
The dentinal tubes, as displayed under a magnifying power of 150 diameters (Plate 11, 
fig. 9, d,), show but a slight curvature in two-thirds of their course from the pulp-cavity, 
but become more curved in the distal third : the terminal bend, convex towards the 
cutting end of the tooth, is more strongly marked than in the incisors of Phascolomys 
or of Macropus. The diameter of the tube is 0 of an inch. The dichotomous 
divisions of the main tubes are sparing, until the greater curve is made, and the ter¬ 
minal branches of these open into minute cells along the line of the enamel, and 
occasionally into cells at some distance therefrom as shown at d', fig. 9. The 
undulation of the fibres of the enamel, e , have a parallelism which renders a seeming 
course transverse to the section more conspicuous than the true direction toward the 
cement, c. This constituent repeats the microscopical characters of that of the 
Wombat’s upper incisor. 
The cast of one of the specimens of an incisor of Sceparnodon Ramsayi (Plate 11, 
figs. 4 and 5), from near Lake Eyre, includes the exposed or working end of the tooth, 
a ; it is bevelled off to an edge from the logitudinally concave to the convex side, 
corresponding to the enamelled outer surface, and which forms, as in other scal- 
priform incisors, the trenchant margin. This edge slightly curves from the outer 
(lateral) to the inner (mesial) border of the tooth. Just above the worn surface of 
the tooth near this border the concave side shows a feeble depression, b, indicative, 
it may be, of pressure by a contiguous tooth. The transverse concavity of the back 
surface of the tooth is rather deeper than in Plate 11, fig. 1, and does not show the 
two longitudinal ridges. This character, if traceable in the actual tooth, might 
suggest a specific difference. 
The fractured, probably implanted, end of the actual tooth may show the termina¬ 
tion of the pulp-cavity, but the indication in the cast is obscure. The length of the 
specimen, in a straight line, is 4-^ inches (90 millims.) ; following the curve it gives 
95 millims. The breadth of the biting end of the tooth is 27 millims.; that of the 
opposite or growing end is 30 millims. This increase indicates a relation to the 
growth of the animal’s body, and suggests that the incisor may have come from a not 
fully-grown individual. There is a corresponding increase of thickness at the (broken) 
implanted end, which gives 13 millims. 
The cast of the largest of these teeth which I have received, showing also the 
largest proportion of the tooth, figs. 6 and 7, repeats the character of the mid-ridge 
along the concave surface ; but a second ridge is more remote and less defined. The 
depression, b, above or root-ward of the abraded working surface is again indicated 
in this incisor. The longitudinal lineation of the convex side of the tooth (fig. 8) 
is of a coarser character than in the portion of tooth, fig. 3, from King’s Creek. 
The length of the cast of the tooth from Lake Eyre, in a straight line, is 5 inches 
(130 millims.) : following the curve it gives 136 millims. : the breadth is 1-| inches 
(35 millims.), and this dimension is the same at both ends of the tooth, indicative of 
its having come from a fully-grown individual. 
