4 PROCEEDINGS OP THE 



mittod the results under the microscope in three sections taken 

 from the same locality, one being under the other. 



As he had anticipated, the growth proved to be hypertrophy of 

 the cementum, one of the three hard structures entering into the 

 formation of the human tooth, viz., enamel, cementum, and dentine. 

 The term exostosis, frequently applied to this growth, was open 

 to exception on account of the fact that there are certain charac- 

 teristic differences between cementum and bone, which any one at 

 all familiar with the microscopical anatomy of these two struc- 

 tures will readily recognize. 



With a view of making these differences apparent to those 

 unacquainted with the subject, he had placed under one of the 

 microscopes a section of bone. This specimen shows a trans- 

 verse section of the Haversian canals with the lacunje and can- 

 aliculi arranged around them in concentric laminae. In the 

 cementum, on the contrary, canals for the passage of blood- 

 vessels are rarel}'^ seen, while the lacunse and canaliculi are quite 

 numerous. 



The three sections from the hypertrophied structure differ from 

 each other in a somewhat remarkable manner, when taking into 

 consideration the fact that they had been in such close contiguity. 



In the first or outer section the lacunae and canaliculi are pre- 

 sented in the usual arrangement of cementum. In the second 

 section, taken immediately under it, there are, in addition to the 

 lacunae and canaliculi, a number of irregular spaces; while in the 



Fiff. 2. 



third section (Fig. 2) the lacunae are largely increased, and the 

 canaliculi are more numerous and increased in length, running 



