90 A MANUAL OF DENTAL ANATOMY. 



like ordinary dentine, but this soon gives place to a coarsely 

 channeled tissue, containing elongated spaces filled with pulp, 

 from which canaliculi, like those of a bone lacuna, branch 

 off in all directions, but do not run far. 



Very many sharks have teeth composed of osteo-dentine, 



FIG. 48 (). 



with an outer dense layer : the tooth of Lamna here figured 

 shows a central core of osteo-dentine, which constitutes the 

 bulk of the tooth j external to this a somewhat thin layer of 

 hard dentine, in which all the dentinal tubes run out at 

 right angles to the surface, but are derived from the channels 

 of the osteo-dentine and not from any single pulp chamber ; 

 while the outermost layer, which is clear and structureless, 



( l ) Tooth of a species of Lamna, consisting of a central mass of vaso- 

 dentine, passing towards its surface into a fine-tubed unvascular dentine. 

 The clear structureless layer on the surface may probably be regarded as 

 enamel. 



