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HANDBOOK OF PHYSIOLOGY. 



nar nucleated cells called odontoblasts. The odontoblasts form the den- 

 tine, while the remainder of the papilla forms the tooth-pulp. The 

 method of the formation of the dentine from the odontoblasts is as 

 follows : The cells elongate at their outer part, and these processes are 

 directly converted into the tubules of dentine (Fig. 172). The continued 



formation of dentine proceeds 

 by the elongation of the odon- 

 toblasts, and their subsequent 

 conversion by a process of cal- 

 cification into dentine tubules. 

 The most recently formed tu- 

 bules are not immediately cal- 

 cified. The dentine fibres con- 

 tained in the tubules are said 

 to be formed from processes of 

 the deeper layer of odonto- 

 blasts, which are wedged in be- 

 tween the cells of the super- 

 ficial layer (Fig. 172) which 

 form the tubules only. 



Since the papillae are to 

 form the main portion of each 

 tooth, i.e., the dentine, each 

 of them early takes the shape 

 of the crown of the tooth to 

 which it corresponds. As the 

 dentine increases in thickness, 

 the papillae diminish, and at 

 last when the tooth is cut, only 

 a small amount of the papilla 

 remains as the dental pulp, 

 and is supplied by vessels and 

 nerves which enter at the end 

 of the fang. The shape of the 

 crown of the tooth is taken by 

 the corresponding papilla, and 

 that of the single or double 

 fang by the subsequent con- 

 striction below the crown, or by division of the lower part of the papilla. 

 The enamel cap is found later on to consist (Fig. 173) of three parts; 

 (a) an inner membrane, composed of a layer of columnar epithelium in 

 contact with the dentine, called enamel cells, and outside of these one or 

 more layers of small polyhedral nucleated cells (stratum intermedium of 

 Hannover); (J) an outer membrane of several layers of epithelium; (c) 



FIG. 171. -Section of the upper jaw of a foetal 

 sheep. A. 1, common enamel-germ dipping down 

 into the mucous membrane; 2, palatine process 

 of jaw. B.- Section similar to A, but passing 

 through one of the special enamel-germs here be- 

 coming flask-shaped; c, c', epithelium of mouth; /, 

 neck; /', body of special enamel germ. C. A later 

 stage; c, outline of epithelium of gum ; /, neck of 

 enamel germ;/', enamel organ; p, papilla; s, dental 

 sacformine:; fp, the enamel germ of permanent 

 tooth. (Waldeyer and Kolliker.) Copied from 

 Quain's Anatomy. 



