THE TEETH. 



619 



puscles under these circumstances is established by such intervening bodies. 

 (See Fig. 265.) 



For the designation of the bioplasson formations between the dentine and 

 enamel, and dentine and cementum, I adopt the term " interzonal layer," as 

 first proposed by Dr. W. H. Atkinson. 



Neck of Tooth. There are certain peculiarities about the minute anatomy 

 of the neck of the human tooth, which, so far as I can judge from the litera- 

 ture within my reach, have not been heretofore mentioned. 



John Tomes, in describing the distribution of the dentinal tubes, says: 

 " Near the neck they stop short of the cementum." This assertion 

 is in accordance with my own observations. In the great majority of 

 teeth neither the canaliculi nor their contents, the dentinal fibers, reach 



aJ 



coa 



FIG. 265. TRANSITION OF DENTINE INTO CEMENT, WITH AN INTER- 

 MEDIATE LAYER OF CEMENT-STRUCTURE. 



D, dentine ; F, bifurcating dentine-fibers, in union with elongated cement-corpuscles, <7i ; 

 these are imbedded in a basis-substance blending with that of dentine. The regular cementum 

 is characterized by branching corpuscles, C*. Magnified 1200 diameters. 



that part of the cementum which surrounds the neck. Near the periphery 

 of the dentine bifurcations of the canaliculi and consequently also of 

 their tenants, the dentinal fibers take place, some of the finest terminations 

 of which run to the boundary between the dentine and cementum. As a rule, 

 the finest terminations of these fibers are lost to sight in a net-work somewhat 

 coarser than that of th^ basis-substance of ordinary dentine. Sometimes the 



