DENTINE 259 



given to the author by Dr. Mackenzie, not only scattered 

 crescentic loops are found in the deeper parts of the dentine, 

 but in several places around the circumference of the pulp 

 channels are seen in the dentine communicating with the 

 pulp, and blood-vessels enter them, the endothelial cells 

 and blood corpuscles being evident within the canals in 

 the dentine. The blood-vessels can be traced along the pulp 

 and seen to cross the odontoblast layer and enter the 

 tubular canals, which penetrate some little distance into the 

 dentine. As, however, these vascular canals pursue a very 



e 



FIG. 161. Vascular loops in tooth of Pseudoscarus. e. Enamel ; 

 d. dentine. Ground section. (x!50.) 



twisted course, more deeply in the dentine only portions 

 of them are seen, cut across (fig. 162). 



In the Cynomys (Prairie Marmot) (fig. 163) the author 

 found the dentine to be permeated by vascular canals in 

 great abundance. He has not been able to find any record 

 of the previous observation of this condition in Cynomys, 

 but it is very evident in ground sections of the incisor and 

 can scarcely have failed to be detected. Short vascular 

 canals in the dentine of many rodents are described by 

 Owen (17) and J. Tomes (21 b). 



From these observations we see that the most permanent 

 and highly developed form of dentine would appear to be 

 tubular or ortho- dentine, and that in the course of develop- 



S 2 



