123 
a diameter of about the 7500th of an inch, which is gradually dimi- 
nished to the 15,000th. When within a short distance of the enamel, 
they suddenly dilate into a more or less oval cell, from which a few 
very minute tubes pass off towards the line of junction of the enamel 
and dentine. The bulbous terminations of the tubes are more con- 
stant and larger about the prominences of the cusps, and diminish in 
size and frequency on the sides of the tooth, where the enamel be- 
comes thin, at the termination of which they altogether cease. The 
bulbs have an average diameter of about 3450, and are in length 
about the 1000th of aninch. In addition to the terminal dilatations, 
the coronal tubes are subject to occasional dilatations in their course. 
It is by no means uncommon to find instances where a peripheral 
layer of cells lies underneath the enamel, into which the dentinal 
tubes pass, and through which an anastomosis is effected; but in 
no other teeth save those of the Tapir do the coronal tubes termi- 
nate in well-marked and uniform cell-like dilatations having distinct 
parietes. I have pointed out several examples, in my paper on the 
teeth of Rodentia, in which these peripheral cells are found, but they 
are irregular in shape, have not distinct parietes, and are entered by 
the ultimate branches of the dentinal tubes ; whereas in the Tapir 
the cells are formed by the expansion of the tubes, which previous to 
the expansion give off few if any branches. Some however subdi- 
vide once or twice in their course ; in which case the smaller of the 
divisions do not commonly dilate into terminal cells, but form anasto- 
moses with other tubes similarly circumstanced. 
In the fangs the dentinal tubes leave the pulp-cavity with a dia- 
meter of the 7500th of an inch, and speedily dilate to the 6000th. 
During the greater part of their course they give off very minute, 
hair-like, short branches; but when near their termination they in- 
crease in size, turn a little upwards towards the crown of the tooth, 
and send out numerous branches, the majority of which pass from 
the lower sides of the tubes. The ultimate branches pass into the 
granular tissue, which, interspersed with irregular cells, forms the 
outer part of the dentine of the fangs. Near the neck of the tooth 
the granular dentine exists as a thin layer, which becomes thickened 
and more opake from the greater number of cells in the lower part 
of the fang. 
Partially obliterated vascular canals enter from the surface of the 
fang, and proceed in straight lines through the dentine to the pulp- 
cavity. In the Indian species similar vascular canals proceed from 
the pulp-cavity towards the ridges of the masticating surface, and 
appear to terminate in loops. They have a diameter of about the 
1000th of an inch. In a molar tooth of the American Tapir, for 
which I am indebted to the Society, vascular canals do not exist in 
the crown. This difference will, if found to be constant, serve to 
distinguish the molars of the two species. Near the extremities of 
the fangs the dentine graduates insensibly into the granular condition, 
and this again into the cementum, without offering any generic pecu- 
harities. 
