474 Zoological Societt/. 



teeth, the deutiual tubes, in addition to describing a double curve, are 

 subject to strongly-marked secondary undulations. The dentinal 

 tubes, as they leave the pulp-cavity for the crown of the tooth, have 

 a diameter of about the 7500th of an inch, vv^hich 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 an inch. 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 ])aper 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 obUterated vascular canals enter from the surface of the 

 fang, and proceed in straight lines through the dentine to the pulp- 

 ca^dty. 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. 



