578 UNGULATES. 



of the tubes, which bifurcate dichotomously 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, (loc. cit. 

 p. 27), and figures (Tab. V, fig. 3) ; but the peripheral smallest 

 branches near the enamel occasionally 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 

 linear dimensions is figured at a, PL 137. The tubes are here 

 separated by rather wider interspaces than those of the incisor, 

 and do not decrease in size so rapidly : the convexity of the terminal 

 bend of the tubes is turned towards the summit of the crown. 



The clear dentinal cells are very, small near the peripheral 

 part of the dentine in the incisor, but increase in size as they 

 approach the pulp-cavity : they are of a sub-circular figure, with 

 bright transparent outlines. 



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 towards 

 its periphery : the clear substance forming the walls of the canals 

 is arranged in concentric layers ; the thickness of the wall being 

 about equal or rather less than the area of the canal. The radiated 

 cells, generally of a full oval, sometimes of an angular form, are 

 chiefly dispersed in the interspaces of the vascular canals, and with 

 their long axis parallel with the plane of the layers of the coats. 

 The finer system of tubes radiating from the cells, and corresponding 

 by minute branches from the vascular canals, freely intercom- 

 municate. In the peripheral cement of the incisors examined by 

 me, I found no vascular canals, but only the radiated cells, and 

 the fine tubuli which I have called ' cemental', and which traverse 

 the cement at right angles to its plane, and communicate with the 



