56 PROFESSOR OWEN ON THE AYE-AYE. 
surfaces for an extent of two lines from the point (fig. 4). The exposed part of the 
tooth resembles the crown of a canine rather than of an ordinary rodent incisor, and 
projects more forward than downward ; but, in the partial investment of enamel, the 
hollow base, and persistent pulp, the Aye-aye’s incisor is a true chisel-tooth. 
The lower incisor (fig. 9, *), which has greater fore-and-aft breadth, but hardly so 
much transverse thickness as the upper one, has the enamel (e) continued further upon 
the sides, especially the outer one; here it is extended fully two lines from the front 
border, and upon the inner side (fig. 7,7) rather more than one line. The long diameter 
of the incisor is 5 lines ; the length, following the convex curve, is 2 inches 7 lines ; 
the depth of the pulp-cavity (fig. 9, p) is 1 inch 8 lines. The exposed part of the 
tooth measures nine lines at its fore part ; but the cutting surface slopes thence, witha 
deep concave curve, to the back part of the alveolar border, where scarcely a line’s 
extent of the concave border of the tooth protrudes. ‘The exposed part of the tooth 
has thus more the shape of the crown of a canine than has that of the incisor above. 
The implanted part of the tooth extends to within five lines of the apex of the coronoid 
process (ib. z). The pulp-cavity, in both upper and lower incisors, is deeply stained 
by the hematosine of the active reproducing matrix. 
In the upper jaw (figs. 6 & 8) the first grinder (p 4) is six lines distant from the 
incisor ; it answers to either the last premolar or last milk-molar in the placental 
diphyodont type; it has an obtuse crown, covered by thick enamel, of a subtrihedral 
shape, the longest side backward, the shortest outward; it is implanted by a simple, 
thick, subconical fang. The second grinder (m 1), answering to the first true molar in 
the type-formula, has an unequal-sided quadrate crown, with the narrowest side forward ; 
the grinding surface is channelled from before backward ; the outer wall is feebly divided 
into two low lobes by an external notch; the inner wall has a convex bulge next the 
palate. ‘The whole crown has a simple but thick coat of enamel: it is implanted by 
two small and short outer roots and one thick and longer inner root: the longest 
diameter of the crown is 2 lines. The third grinder (m 2) resembles the former, but 
its front side is as long as the back one: it is similarly implanted. ‘The last grinder 
(m3) has a full oval crown, with the’small end outward ; the grinding surface has a middle 
depression surrounded by three low tubercles, the inner one the largest, the hind one 
much the smallest. It is implanted by a short thick fang, slightly notched at the apex. 
The position of the crowns of these teeth is such that the direction of their interspaces is 
oblique, from within, outward and forward ; but the grinding surface looks directly 
downward. A magnified view of that surface is given at fig. 10, Pl. XX. 
The three lower grinders are true molars, and are a little in advance of the crowns 
of their homotypes above. Each has a shallow longitudinal depression on its grinding 
surface, with simple undivided outer and inner boundaries, uniting at their fore part in 
the first grinder, and with a very small lobe interposed behind in the last. Each has a 
simple cap of enamel, like the molars above. The mid-molar (m 2) is rather the largest, 
