THE CURVES OF THE DEXTIKAL TUBES. 133 



their thickness. In some parts of the dentine of the 

 incisor they are more closely crowded together, espe- 

 cially near their origin from the pulp-cavity. Their 

 secondary gyrations describe a curve of about y^Voth 

 of an inch in length. These subside in the slender 

 terminations of the tubes, which bifurcate dichoto- 

 mously once or twice, and send off small lateral 

 branches near the enamel. The small lateral branches 

 are chiefly visible in the peripheral third part of the 

 tubes, and are sent off at very acute angles, except in 

 the strongly and irregularly bent origins from the 

 pulp-tract. I have never seen these small branches of 

 the dentinal tubes terminating in radiated cells, like 

 those of cement and bone, as Retzius describes; but 

 the peripheral smallest branches near the enamel occa- 

 sionally dilate into corpuscles much more minute 

 than the radiated cells, as they do in the teeth of most 

 quadrupeds. 



" The dentine, as seen in a longitudinal section of 

 the crown of a molar, by a magnifying power of three 

 hundred hnear dimensions, is figured at a, Plate 137. 

 The tnbes are here separated by rather wider inter- 

 spaces than those of the incisor, and do not decrease 

 in size so rapidly. The convexity of the terminal bend 

 of the tubes is turned toward the summit of the crown. 

 In the incisor, the clear dentinal cells are very small 

 near the peripheral part of th« dentine, but increase in 

 size as they approach the pulp-cavity. They are of a 

 sub-circular figure, with bright, transparent lines. 



"The central cement in the crown of the incisor is 

 permeated by vascular canals, separated by intervals of 

 from two to three times their own diameter, directed 

 in the middle of the substance in the axis of the tooth, 

 but diverging like rays obliquely toward its periphery. 



