204 LABYRINTHODONTS. 



for a certain distance from the base, and radiating outwards from its 

 circumference a series of vertical plates, which divide into two, once 

 or twice before they terminate at the periphery of the tooth. 



Each of these diverging and dichotomizing plates gives off 

 throughout its course smaller processes which stand at right angles or 

 nearly so to the main plate ; they are generally opposite, but sometimes 

 alternate : many of the secondary plates or processes which are given 

 off near the centre of the tooth, also divide into two before they ter- 

 minate ; and their contour is seen, in the transverse section, to 

 partake of all the undulations of the folds of cement, which 

 invest and divide the dentinal plates and processes from each 

 other. 



The dental pulp-cavity is reduced to a mere line about the upper 

 third of the tooth, but throughout its w^hole extent fissures radiate from 

 it, corresponding in number with the radiating plates of dentine. 

 Each fissure is continued along the middle of each plate, dividing 

 where this divides, and extending along the middle of each bifurcation 

 and process, to within a short distance of the line of cement. The 

 pulp-fissure commonly dilates into a canal at the origin of the lateral 

 processes of the radiating plates, before it divides to accompany and 

 penetrate those processes. 



The main fissures or radiations of the pulp-cavity extend to within 

 a line or half a line of the periphery of the tooth, and suddenly dilate at 

 their terminations into spaces, which, in transverse section are subcir- 

 cular, oval or pyriform (PL 64, bb) : the branches of the radiating lines, 

 which are continued into the lateral secondary plates or processes of 

 the dentinal lamellae, likewise dilate into similar and generally smaller 

 spaces. All these spaces or canals, in the living tooth, must have 

 been occupied by corresponding processes of the vascular pulp : they 

 constitute as many centres of radiation of the fine calcigerous tubes, 

 which with their uniting clear substance constitute the dentine. 



Throughout every part of this complicated tooth, the calcigerous 

 tubes were found, in their course, to obey the usual law, radiating or 

 converging, with primary curvatures and secondary undulations, at 

 right angles or nearly so to the surface of the dentine which the cement 

 invests. The number of these calcigerous tubes, which are themselves 



