296 



DIGESTIVE ORGANS. 



[sect. 138. 



a\ 



iMi 



'•'/n 



The conjunction of the enamel-fibres is effected without any- 

 visible intermediate substance, and is very intimate. I have not, 

 hitherto, been able to convince myself that canals regularly exist 

 between the enamel -fibres ; still there are, doubtless, not unfre- 

 quently cavities of various kinds in the enamel. Among these I 

 reckon, 1, the above-mentioned continuations of the dentinal canals 

 into the enamel, and the elongated cavities upon the boundary of the 

 dentine, occasioned by the enlargement of these canals (fig. 125, c) ; 

 Kg. 125. an d 2, breaches in form of fissures in the middle 



and outer parts of the enamel (fig. 125,6). The 

 latter are not connected with the former, are 

 never entirely absent, and frequently exist in ex- 

 ceedingly large numbers, as narrower or wider 

 fissures, which, however, are never filled with air. 



The course of the enamel-fibres is, in general, 

 the same as that of the dentinal canals of the 

 crown, although larger curvatures occur in them 

 only upon the masticating surface. All the 

 enamel-prisms, moreover, do not appear to extend 

 through the entire thickness of the enamel, al- 

 though this is certainly the case with the majority. 

 Peculiar, also, are the decussations of the enamel- 

 prisms, which take place in transverse planes of 

 the tooth in such a manner that not separate 

 fibres, but entire band- shaped layers of them (cor- 

 responding to fine, externally visible circular lines, 

 o - o8'" to o , i2" / in thickness), extend in very 

 various directions (each layer preserving the same 

 direction), from the dentine as far as the outer 

 surface of the enamel: which arrangement gives 



Human dentine and t i • • -n ^ 1 



enamel; magnified 350 to perpendicular sections, especially alter they are 



times, a. Enamel-cu- . _ •l-ii 1 i •  i t 



me-, b. enamei-fibres, moistened with hydrochloric acid, a peculiar 



with fissures between . . . , 



them and transverse striated appearance (fig. 122), inasmuch as when 



lines; c. large cavities J~ i i 



in the enamel; a. so treated, alternate darker transverse sections, 



dentine. . />i •■ 



and lighter longitudinal aspects or the prisms 

 come to view. Such decussations constantly occur, also, upon the 

 masticating surface, and layers of enamel run here generally in an 

 annular form, so that upon the molars they describe circles, and 

 upon the cutting teeth ellipses; but towards the middle of the 

 masticating surface, irregularities of these lines occur, which cannot, 

 as yet, be clearly made out. To be distinguished from the colourless 

 strise, which indicate the above-described stratified arrangement of 

 the enamel-fibres, are certain brownish lines or colourless stria, 



