b ' PROCEEDINGS OF THE 



tion of hypertrophied root of a molar tooth ; heraipterous insect 

 (Tirtgis arcuata); longitudinal section of a deciduous incisor and 

 of a molar tooth. Dr. McJ^^uillen directed particular attention 

 to the last-named specimen as having a practical significance 

 bearing upon the diseases and treatment of the teeth. Under the 

 microscope a fissure (Fig. 3) inappreciable to the naked eye could 



Fig. 3. 



be seen passing through the enamel and enlarging into an oval 

 cavity near the junction with tlie dentine, also a number of inter- 

 globular spaces in the dentine in close proximity to the fissure 

 in the enamel. This fissure and the interglobular spaces, being 

 due to defective formation, are therefore predisposing causes of 

 decay. While such a fissure would be inappreciable to the naked 

 eye, a delicate probe would readily pass into it, and a tooth found 

 in such a condition should be filled immediatel}', so as to prevent 

 the development of caries ; for so long as acids, decomposed 

 food, and other exciting causes are prevented from coming into 

 contact with the defective dentine, the predisposing cause remains 

 dormant. This specimen closely demonstrates the importance of 

 promptly filling the small cavities formed in the depressions on 

 the grinding, buccal, and lingual surfaces of the bicuspids and 

 molars, and on the palatine surface of the incisors and canines. 



