LABYRINTHODONTS. 195 



having their long axis vertical, or in the direction of the axis of the 

 tooth : these cells do not extend into the substance of the tooth 

 itself. The dentine is composed of fine calcigerous tubes and the 

 intermediate clear substance, the minute cells of which are unusually 

 conspicuous and abundant. In a completely formed tooth no trace of 

 a pulp-cavity is discernible in the prominent crown. The calcige- 

 rous tubes are continued into the body of the tooth at once from 

 the subjacent bone, in the interspace of the transverse fissure first 

 mentioned. The tubes nearest the external and the internal periphery of 

 the base of the tooth incline with a gentle curve towards those surfaces ; 

 but the greater number proceed vertically, and nearly parallel with 

 each other, to the convex line anterior to the inflected apex of the 

 tooth, where their extremities are slightly bent outwards, except in a 

 few of the tubes nearest the apex which follow its inward curvature. 

 The secondary undulations and branches of the calcigerous tubes are 

 very elegant and conspicuous : the terminal branches of these tubes 

 end in a rich border of calcigerous cells. The dentine is not com- 

 plicated with medullary canals or inflected folds of the external 

 cement. The convex margin of the upper half of the tooth is coated 

 with a layer of enamel. The concave border and the basal half of 

 the opposite margin exhibit a thin layer of cement. The enamel, 

 viewed by transmitted hght, presents the same dull brownish tint as 

 that of the saurian and mammalian teeth ; and has a minutely undu- 

 lating fibrous texture. 



LABYRINTHODONTS. 



87. The dental system in the extinct genus Labyrinthodon is more 

 formidable than that of any existing Batrachian : and principally 

 differs, as regards its more obvious characters, in the implantation 

 of the teeth in distinct sockets, and in the development of certain of 

 the anterior teeth of both jaws into large and formidable tusks. 



A close-set series of subequal teeth extends along the alveolar 

 border of both upper and lower jaws, and along the anterior part of 

 the outer margin of each broad vomerine bone : two or three canine- 

 shaped teeth, at least three times the size of the serial teeth, are placed 

 in the intermaxillary bones and at the anterior and external angle of 



o2 



