260 MICROSCOPIC ANATOMY OF THE TEETH 



ment to higher forms the vasodentine structure has gradu- 

 ally disappeared, only existing here and there as vestiges ; 

 but in Sarcophilus and Cynomys there would appear to 

 be a more complete indication of reversion to the original 

 structure. 



A similar argument applies to the tubular enamel of 

 marsupials, where we see a reduction of the tube system 

 even in the same class of the mammalia, until in the Wombat 

 it has ceased to be apparent, but in Hymx, Dipus, and Sorex 



FIG. 162. Dentine of Sarcophilus ursinus. Capillary 

 vessels entering dentine. ( x 350.) 



among the higher mammalia we find a more or less complete 

 reversion to the original tubular enamel, and in man and 

 other mammals a slight penetration by tubes shows that all 

 traces of such a condition have not been finally lost. 



Osteodentine or Trabecular Dentine. Osteodentine is very 

 nearly allied to bone in structure. There is no distinct 

 pulp cavity, but the interior of the tooth is traversed by 

 bony trabeculae, the interspaces being occupied by medullary 

 canals and blood-vessels which may be considered to take 

 the place of the pulp. The large medullary channels at the 

 base of the tooth divide and ramify like the branches of 



