FORMATION OF THE EXAMEL. 



319 



Fi- 221. 



of the dentine, wliicli is thus as it were moulded upon them, so as to 

 form the tubules in which, therefore, the cell-processes are now enclosed. 

 The same cell may continue to spin out a filament until the tubule is 

 completed in its whole length, and it may be that a cell sends out two 

 or more processes, coalescing into one as the cell recedes, so that a 

 branched tubule is thus produced. 



According to Waldej'er (•n'itli whom Boll sems to agree) it is the substance or 

 protoplasm of the cells which becomes trans- 

 formed into the dentinal matrix, all except the 

 central iDart, which remains unaltered, occupying 

 the tubule, and is prolonged by another cell lying- 

 deeper in the pulp, with which the first is in 

 connection, and so on in succession. Moreover, 

 he refers the anastomosis of neighbouring tubules 

 to the existence of communicating branches 

 between adjacent cells. 



The collogenous basis of the dentinal 

 matrix is at first uncalcified (fig. 220, h), 

 but the material of calcification soon begins 

 to be deposited in nodules or globules, 

 Avhicli run together into a uniform hard 

 substance {a). In iiarts where this coal- 

 escence partially fails the uncalcified matter 

 between the globules shrinks up when the 

 tooth has become dry, so as to leave the 

 interglobular spaces previously described 

 (p. 310). The globular mode of deposition 

 is indicated also by tlie inner surface of 

 the growing' dentine, which is nodulated 

 (Czermak); and, indeed, separate nodules 

 may sometimes be seen in the soft tissue 

 of the growing matrix (see fig. 220). 



Purkinje and Raschkow described a fine pel- 

 lucid homogeneous membrane {inniihrdna prc- 

 foriiKittcti} covering the surface of tlie pulp before 

 the commencement of calcification, but the exist- 

 ence of such a coating is at )jest doubtful, and 

 at any rate Avhether present or not, it appears 

 to be of no significance in the development of 

 the teeth. It may possibly be the first uncalcified 

 dejDosit of dentinal matrix. 



The Enamel. — The surface cells of the 

 enamel-germ line the dental sac in the 

 form of a tesselated or cubical epithelium 

 (fig. 221, e). On the other hand the cells 

 which lie next the surface of the pulp 

 become elongated and attenuated into a 

 prismatic shape, precisely like a columnar 

 epithelium {d fig. 221). Tlie central cells, 



Fig. 221. — A Section through the Enamel Organ and Dental Sac from 

 OF A Child at Birth (from K<3lliker). 250 Diameters. 



a, outer dense layer of the dental sac ; h, inner looser texture of the 

 capillary blood-vessels and a somewliat denser layer towards the enamel 

 spongy substance ; d, inner cells ; and e, outer cellular layer of the enamel or 



THE Tooth 



same with 

 organ ; c. 



