52 



SPECIAL HISTOLOGY. 



apart, which arise from slight varicosities, and give the 

 fibres a certain resemblance to muscular bundles, or rather 

 Fig 190 colossal muscular fibrils. They 



certainly do not indicate a 

 cellular composition. If the 

 action of the hydrochloric acid 

 be allowed to go on, the fibres 

 soon become quite pale, the 

 transverse striation disappears, 

 and nothing remains but a deli- 

 cate framework corresponding 

 with the previously solid fibres, 

 and which often presents cer- 

 tain appearances of tubes. In 

 the end this also becomes 

 almost completely destroyed 

 by the action of the acid, so that in teeth which have been thus 

 macerated hardly anything remains of the enamel, which does 

 not, like the dentine, retain its form. 



The prisms of the enamel are united very intricately with- 

 out any intermediate substance. I have not been able to 

 convince myself that canals constantly exist between the 

 prisms, 1 but it is certain that cavities of various kinds may be 

 not unfrequently found in the enamel. Such, for instance, are 

 — 1. The continuations of the dentinal canals into the enamel, 

 to which reference has been made above, with the elongated 

 cavities at the border of the dentine which arise from their ex- 

 pansion (fig. 191, c) ; and 2. The cleft-like gaps in the middle 

 and external portions of the enamel (fig. 191), which are not 

 in communication with the preceding, are never entirely ab- 

 sent in any enamel, and often occur in very great numbers, as 

 narrower or wider spaces which, however, never contain air. 



Fig. 190. Enamel prisms isolated, after the slight action of hydrochloric acid, 

 x 350. From Man. 



1 [With respect to this point, opinions differ; Todd and Bowman consider that 

 canals normally exist between the enamel prisms. Tomes finds canals in the 

 enamel prisms of young animals, and sometimes in a part or the whole length of 

 them in old teeth. KSlliker (Mikr. Anat. 77) has not yet observed any such cases. 

 Czermak (I.e. p. 13) believes that, in a few cases, he has observed "very numerous 

 delicate enamel tubules arranged in close series."-^EDS.] 



