V 



THE DENTAL TISSUES. 



61 



therefore, are markings, ranged parallel with the exterior of 

 the dentine, which are due to the curvatures of the dentinal 

 tubes. 



The " contour lines " of Owen, even in his own works, 

 include markings of both classes : i. e., those due to the 

 curvature of the dentinal tubes, and those due to laminae of 

 interglobular spaces, such as are met with in the teeth of 

 Cetacea. Ketzius had seen and described contour markings 

 due to interglobular spaces, though his name is not usually 

 associated with them, the " brown striae of Retzius " being 

 markings in the enamel. 



The tubes as they pass outwards often divide into two 

 equally large branches ; they also give off fine branches, 

 which anastomose with those of neighbouring tubes. In the 



crown of a human tooth these fine branches are compara- 

 tively few, until the tube has reached nearly to the enamel, 

 but in the root they are so numerous as to afford a ready 

 means of distinguishing whence the section has been taken. 

 The small branches above alluded to are given off at right 

 angles to the course of the main tube, which, however, itself 

 frequently divides and subdivides, its divisions pursuing a 

 nearly parallel course. 



The tubes are subject to slight varicosities, and their 



( ] ) Termination of a dentinal tube in the midst of the dentine human. 



