626 THE TEETH. 



but as the outer -surface of the tooth exceeds the inner one in extent, the 

 tubes slightly diverge in their course and divide, decreasing in diameter to 

 their peripheral extremities, and rapidly so near their terminations, where 

 they become irregularly flexuous and often interlaced. The dichotomizing 

 calcigerous tubes send off from their sides much more minute branches, which 

 quickly divide and subdivide in the interspaces of the trunks and penetrate 

 the dentinal cells. The cement, which, with the dentine, is present in all teeth 

 of mammalian animals, is characterized, except where it forms an extremely 

 thin layer, by the radiated calcigerous cells, usually arranged in lines or 

 layers parallel with the surface of the cemental coat, and with each other. 

 The enamel consists of more or less curved or wavy prismatic fibers, averaging 

 about l-4000th of an inch in diameter, and transversely striated." 



John Tomes * says of enamel : " The organic matter said not to belong to 

 the class of gelatinous tissues, but to be closely similar to epithelium in 

 its chemical relations, is stated not to exist between, but in the substance 

 of the prisms (Hoppe-Seyler). The enamel is made up of parallel fibers, 

 which lie in close contact with one another, no intervening substance being 

 demonstrable." On dentine : " In the crown of the tooth the dentinal tubes 

 terminate by forming loops, or become too minute to be traced, or pass into 

 the enamel and become lost. In teeth the dentine of which is imperfectly 

 developed, the terminal branches are lost among, or end in, the minute cavi- 

 ties which abound in the layer at or near the peripheral surface of the dentine. 

 Near the neck they stop short of the cementum, but toward the end of the 

 root they not uncommonly pass into the cementum and connect themselves 

 with the lacunae. By the extension of the dentinal tubes into the enamel and 

 into the cementum, a connection is formed more intimate than mere superposi- 

 tion and adhesion of the one to the other would have established. In prepara- 

 tions in which we are fortunate enough to retain a portion of the pulp with 

 the dentine, it may readily be seen that the soft fibrils are processes of the 

 cells known as ; odontoblasts,' which constitute the peculiar layer called the 

 membrana eboris. It is absolutely certain that no structures other than 

 nerves have the power of conducting sentient impressions, and hence it is not 

 quite necessary to assume that the dentinal fibers are actual nerves before 

 allowing them the power of communicating sensation. The greater degree 

 of sensitiveness observable in the dentine immediately below the enamel 

 that is, at the point of ultimate distribution of the dentinal tubes, and conse- 

 quently of their contents may be fully accounted for on the supposition 

 that the latter are organs of sensation, the highest sensibility of which is 

 confined to their branches." On cementum: " The canaliculi of neighboring 

 lacunae anastomose freely with each other, and establish a net-work of com- 

 munication throughout the whole body of the cementum, and occasionally 

 become connected with the terminal branches of the dentinal tubuli. It is 

 to the description of primary bone that the cementum of the teeth is most 

 closely allied, and from that it is difficult to point out any distinguishing 

 structural character." 



Charles S. Tomes t maintains of enamel: "In perfectly healthy human 

 enamel the fibrillar arrangement is not so very strongly marked ; the fibers 

 are solid, are in absolute contact with one another, and have no demonstrable 

 intervening or uniting substance, or else inter-spaces would be left, which is 



* " System of Dental Surgery," 1873. t " Manual of Dental Anatomy," 1876. 



