258 MICROSCOPIC ANATOMY OF THE TEETH 



in very early forms, but in the higher Mammalia the tubular 

 or ortho- dentine seems to have supplanted in most cases the 

 probably more primitive vasodentine. 



In Sargus ovis loops are seen within the dentine which 

 appear to be the remains of vascular tubes, and may indicate 

 that the dentine of Sargus was derived from a vasodentine. 

 Similar loops at the base of the tooth in Sargus are evidently, 

 in the author's preparations from freshly-fixed material, in 

 communication with the pulp cavity, while isolated crescentic 

 forms are seen deeply in the dentine. In ground preparations 



FIG. 160. Vascular network in centre of incisor tooth of Sargus 

 ovis. e. Enamel ; d. dentine. Ground section. (x!50.) 



of similarly preserved incisor teeth of Sargus, what certainly 

 appear to be vascular canals are seen passing out from the 

 narrow prolongation of the pulp cavity in the crown and 

 forming a branched network which reaches up to the enamel 

 (fig. 160). This was found in all the teeth examined, when 

 they were so cut as to expose the central part of the axis 

 of the tooth, and this branching system appears to be 

 confined to this area and to extend in a direction parallel 

 to the flattened surfaces of the. tooth. Again, in Scarus, 

 loops having every appearance of being vascular tubes are 

 seen in abundance in the dentine, and at the enamel margin 

 they distinctly project into the enamel (fig. 161). 



In the teeth of the Tasmanian Devil (Sarcopkilus ur sinus) 

 of which a good preparation, preserved in formol, was 



