468 STRUCTURE AND DEVELOPMENT OF TEETH, W. WALDEYER. 



fresh teeth, examined with high powers (500 1,000), it is not 

 difficult to recognise, especially in the central section of the 

 course of the tubules, which is of considerably larger diameter, 

 the pale homogeneous dentinal fibre. The lining of the tubules 

 (dentinal sheaths) can only be satisfactorily seen in cross 

 section, when they appear as delicate yellowish rings, in the 

 interior of which the transverse section of the dentinal fibre is 

 perceptible in the form of a minute dark point. I, at least, 

 agree with Kolliker (58) in this interpretation of the appear- 

 ances seen on cross section. Carious teeth prove very service- 

 able in exhibiting these relations * The dentinal tubules are 

 best examined in fine sections dried in air. They then make 

 their appearance, filled with air, in the form of strongly defined 

 very dark tubules or lines, enabling them to be traced to their 

 finest ramifications. 



In regard to the mode of peripheric termination of the dentinal 

 tubuli no positive conclusion can be drawn. Yet exact infor- 

 mation on this point is of considerable importance, because 

 Tomes (29) has directed attention to the sensibility of the 

 peripheric portion of the dentine. 



Wherever the terminal loops occur the dentinal tubuli 

 must also end in the same manner; nevertheless, it is 

 difficult to demonstrate actual terminal loop-like structures. 

 Extremely fine processes of the dentinal tubuli run towards 

 the enamel, and are lost at the surface of the dentine. At this 

 part also larger or smaller irregularly defined cavities are 

 found, the interglobular spaces of Czermak (33), which will 

 be more fully considered hereafter. The dentinal tubuli open 

 into these interglobular spaces, and from them again fine 

 processes extend towards the enamel, A direct passage of the 

 dentinal tubuli into the enamel does not occur. 



Tomes (29) and Kolliker (58) are strongly of opinion that some of the 

 dentinal tubuli, with their soft contents, penetrate into the enamel. 

 This they think especially occurs amongst the Rodents and Marsupials. 

 I have not, however, been more successful than Hertz (52) in con- 



* In the vicinity of carious portions of tooth, both the soft dentinal 

 fibres and the dentinal sheaths are thickened, so that in transverse sections 

 both come very clearly into view. 



