TEETH. DEVELOPMENT OF DENTINE 



287 



Incisors of Ox. 



Dentine. 

 Phosphate of Lime, with trace of) gg ^ 



fluate of lime . J 



Carbonate of Lime 7.00 



Phosphate of Magnesia 0.99 



Salts ... 0.91 



Chondrin (?) . . 30.71 



Fat 0.82 



100.00 



Enamel. 

 81.86 



9.33 

 1.20 

 0.93 

 6.66 

 0.02 



100.00 



Cement. 

 58.73 



7.22 

 0.99 

 0.82 

 31.31 

 0.93 



100.00 



Fig. 79. 



279. The Dentine and its modifications, the Enamel, and the Cementum, origi- 

 nate in three distinct structures ; which may be termed respectively, the dentinal- 

 pulp, the enamel-pulp, and the capsular or cemental-pulp ; the whole forming 

 the "matrix" from which the entire tooth is evolved. The Dentinal pulp is 

 always the first-developed part of the matrix; and it makes its appearance in 

 the form of a papilla, budding out from the free surface of a fold or groove of 

 the mucous membrane of the mouth. The substance of this papilla at first con- 

 sists, according to Mr. Tomes, 1 of a very delicate areolar tissue composed of 

 delicate fibres and bands, whose meshes are occupied with a thick, clear, homo- 

 geneous fluid or plasma, scattered through which 

 are a number of nucleated cells ; the whole being 

 enclosed in a dense, structureless, pellucid mem- 

 brane. The papilla is copiously supplied with 

 bloodvessels, which originate in a trunk that 

 enters its base (Fig. 79), and then ramify and 

 spread through its whole substance, at last form- 

 ing a capillary network which terminates in loops 

 near its apex. These vessels are accompanied 

 by nerves, which also have looped terminations. 

 The changes in which the conversion of the 

 papilla into the tooth-substance consists, com- 

 mence near the coronal surface; where the cells 

 of the pulp, lying beneath its investing mem- 

 brane, are found to have undergone enlargement, 

 and to be thickly scattered at pretty regular in- 

 tervals through a sub-granular uniting medium, 

 the intermediate areolar tissue having now dis- 

 appeared (Fig. 80, A) ; the cavities of the cells 

 are occupied by granular matter. The blood- 

 vessels now begin to retreat from the coronal 

 surface of the papilla, so that few are seen in the 

 part which exhibits this second stage of develop- 

 ment. At a later period, the cells of the pulp 

 exhibit a regular linear arrangement (B), their 

 extremities coming into close approximation with 

 each other; and the intermediate connecting 

 substance acquires a much firmer character. Each cell, after falling into line, 

 undergoes transverse fission, and each division elongates ; so that in this manner 

 their extremities are brought into close apposition. Whilst this is taking place 

 their cavities also increase in length, and extend to the extremities of the cells ; 

 and at last the intervening septa disappear, so that the cell-cavities become con- 

 tinuous, and constitute tubes (c). At the same time, the calcifying process is 

 taking place in the intercellular substance, and in the thick walls of the cells ; 



Vessels of DenM Papilla. 



'Lectures on Dental Physiology and Surgery," p. 84. 



