86 MICROSCOPIC ANATOMY OF THE TEETH 



treated with alcoholic fuchsin, these radiating lines are 

 strongly coloured by the stain, and a broad band of more 

 diffuse staining passes a little way into the enamel at the 

 base of the depressions (fig. 40). 



The large tubes of osteodentine which form the bulk of 

 the tooth give out tree -like branches that divide and sub- 

 divide, their ultimate fine ramifications passing outwards 

 and crossing and mingling with the tubes from the outer 

 surface. Fine tubes also pass into the enamel from all 

 parts of the outer surface, although larger and more deeply 

 penetrating in the radiating bundles which start from the 

 base of the depressions. The two systems of tubes appear 

 to communicate with one another at the inner margin of 

 the enamel by their finest subdivisions. The line of junction 

 between enamel and dentine is very imperfectly defined, 

 but in most sharks the boundary line is much more distinct. 



In many sharks the tubes from the osteodentine enter the 

 enamel more or less in bundles and branch and anastomose 

 within it, forming a network. Many of the dentinal tubes enter 

 lacuna-like spaces in the enamel. The tubes from the out- 

 side enter in more or less parallel straight lines, and appear 

 to communicate with the dentinal system in the deeper part 

 of the enamel. 



In Lamna cornubica (the Porbeagle shark, fig. 41) the 

 typical osteodentine core sends large branches into the 

 enamel, which also shows traces of lamination and short 

 transverse markings. The delicate striae from the outside 

 take the stain faintly and the blending of the dentine 

 and enamel at their junction is imperfectly defined as in 

 Cestracion. These markings or striae from the outside have 

 not been hitherto shown conclusively to be of a tubular 

 nature. Tomes speaks of them as striae and considers it 

 doubtful whether they are of a tubular nature or merely 

 distinctly shown prisms, and says he has never been success- 

 ful in getting coloured fluids to enter them (18 e). 



The author has shown, however, that, in the sharks, in 

 the Sargus, and in all the other fishes examined for this 

 purpose, the markings are most certainly tubes, and are 

 quite independent of the columns of prisms which are also 

 seen at the margin of the enamel following a course parallel 



