THE TEETH. 



45 



Fig. 187. 



very narrow yellowish border, which is what I consider to be 

 the actual wall. That such is the case, appears from the 

 examination of transverse and oblique sections of canals filled 

 with fluid, in which short, yellow tubules and small rings of 

 almost the same diameter as that of the cavities of the canals, 

 may be clearly recognised. 



The dentine occasionally presents indications of lamination 

 in the form of arched lines running more or less parallel and 

 at different distances, often quite 

 close together (fig. 187); which 

 in transverse sections appear as 

 rings, and are especially distinct 

 in the crown. These, the contour 

 lines of Owen,i are not the same 

 with the glistening, indistinctly 

 defined strise observedbySchreger, 

 which run exactly parallel to the 

 pulp cavity, and arise from the pri- 

 mary curvatures of the dentinal g - 

 canals, and which are the expres- 

 sion of the laminar mode of deposit 

 of the dentine. In animals they 

 are at times singularly beautiful, 

 especially in the Cetacea and 

 Pachydermata (Zeuglodon, Du- 

 gong, Elephant), and also in the 

 Walrus. Here as well as in fossil 

 teeth we very frequently observe 

 a breaking up of the dentine into 



Fig. 187. Perpendicular section of the apex of an incisor tooth (human), x 7 : 

 a, pulp cavity; b, dentine; c, arched contour lines, with interglobular spaces; d, 

 cement ; e, enamel, the various directions of the fibres being indicated ; ff, lines 

 of colour of the enamel. 



1 [This is not exactly correct. The term "contour lines," as used by Professor 

 Owen ('Report of British Association' for 1838, p. 135, and ' Odontography,' pp. 460, 

 464, 641) includes both descriptions of markings mentioned in the text, but is 

 more especially employed for Schreger's. The ordinary contour lines, in fact, are 

 stated by Professor Owen to proceed from " a short bend " of the tubuli " parallel with 

 the outer contour of the crown;" from these, the Professor distinguishes the "strong 

 contour lines," in the ivory of the elephant's tusk, as being produced by " strata of ex- 

 tremely minute opaque cellules." It should be observed, however, that Retzius had 



