THE ALIMENTARY TRACT. 



279 



a. The dentine is a liomog-eneous substance pierced by numerous 

 tubules [I)), which arise at the j)ulp-eavity and course in a parallel 

 direction to the surface of the 

 dentine, where they form a 

 rich network with irregular, 

 interg'lomerular sj)aces. The 

 inner surface of the dentine 

 is roug-h, through the presence 

 of numerous small, dark 

 tubercles, 



/3. The enamel covers the 

 dentine on the apical portion 

 of the tooth. It has tubes 

 coursing through it, which are 

 continuous with those of the 

 dentine, and jDresents also 

 circumferential striations (Fig*. 

 i8i III). 



y. The tooth cuticle [Catl- 

 cula dentis) is colourless and 

 covers the enamel. It is 

 highly refractive, very trans- 

 parent, and very resistant to 

 chemical reagents. From the 

 apex, towards the Cnis/a 

 jjeirosa, it thins very rapidly, 

 but is continued sufficiently 

 far to cover a portion of the 

 Crusta petrosa. 



Ô. The Crusfa pefrosa resembles bone, except that it contains no 

 Haversian canals ; it possesses cells which resemble bone corpuscles, 

 and are usually somewhat rounded or oval and communicate with 

 each other by their processes ; for the most part it is homogeneous 

 and free from cells (Hertwig). 



e. The pulp-cavity contains a connective-tissue very rich in 

 cellular elements ; those cells adjacent to the dentine are arranged 

 in a layer [Membraiia ehoris) which has somewhat the appearance of 

 a layer of epitheliiun. The cells (odontoblasts) of this layer are 

 spindle-shaped, and send processes (dentinal fibres) into the dentinal 

 tubules. A small blood-vessel can be traced into each cavity, but 

 as yet no nerve has been found in the pulp-cavities. 



II 



I. Transvex'se section uf the premaxillaiy bnue to 

 show attachment of the teeth ; after Hertwig. 

 Magnified 22 times. 

 Dentine and enamel ; after Hertwig. Magnified 



500 times. 

 Enamel : after Hertwig. Magnified 500 time.s. 

 A Blood-vessel of the pulp-cavity. 

 Crusta petrosa. 

 Dentine. 



Processvis dentalis. 

 Layer of epithelium. 

 Tooth cuticle. 

 Reserve. 

 Enamel. 

 Cutaneous glands. 



