598 UNGULATES. 



wider than the interspaces of the tubes, extend here and there 

 from the pulp- cavity, in the directions 'of the tubes and of the 

 short vascular canals; the tubes next these tracts make a sudden 

 bend obliquely across them with wider clear intervals. The tubes 

 divide sparingly in the first half of their course ; and, not decreasing 

 much in diameter, appear closer packed as they approach the 

 enamel. In the outer third of their course they make here and 

 there abrupt secondary bends, and send off the minute lateral 

 branches from both sides. Here and there the tubes present slight 

 partial enlargements ; they very gradually decrease in size, until 

 close to the peripheral stratum of minute opake cellules, (PL 139, 

 cZ" d^^) where they chiefly end by a bifurcation, the forks diverging 

 at an angle of 45°, and bending in opposite directions, sometimes 

 anastomosing, sometimes irregularly dilating into, or communicating 

 with, the opake cellules. The traces of the compartments of the 

 basal substance, or dentinal cells, are very faint ; they are best 

 seen in transverse sections, as in PI. 139, d^ d^ ; especially that 

 part of their contour next the enamel which curves across from 

 four to five of the dentinal tubes ; the compartments or cells increase 

 in size as they approach the pulp-cavity, but soon become fainter 

 and disappear from view. 



The contour lines (ib. / /) are unusually conspicuous and nume- 

 rous, with interspaces of ^„th of an inch ; they are not due to abrupt 

 parallel bends of the tubes, nor to branches or opake cells, but to 

 a slight increase of opacity of the basal substance which seemed 

 to be due to oblique cracks along the lines in question. The enamel 

 fibres (ib. e e), in a transverse or horizontal section of the crown, 

 proceeded from the surface of the dentine across the thickness of 

 the layer, with a gentle degree of flexuosity ; their diameter is ^th 

 of an inch. I could discern only a faint granular appearance in 

 the fibre, certainly no transverse segmentation. The whole thickness 

 of the layer of enamel is traversed by contour lines at varying 

 intervals, running parallel to the border of the dentine. Here 

 and there the fissures occur at the dentinal surface of the enamel, 

 with irregular or stronger bends of the adjoining fibres. In a vertical 

 section of the enamel the fibres were seen to run more obliquely 



