366 



ANATOMY OF VERTEBRATES. 



243 



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 with- 

 in a line or half a line of the 

 periphery of the tooth, and sud- 

 denly dilate at their terminations 

 into spaces, which, in transverse 

 section, are subcircular, oval, or 

 pyriform, p : the branches of the 

 radiating lines, which are conti- 

 nued into the lateral secondary 

 plates or processes of the dentinal 

 Iamella3, likewise dilate into simi- 

 lar, and generally smaller spaces. 

 All these spaces, or canals, in the 

 living tooth, must have been oc- 

 cupied by corresponding processes 

 of the vascular pulp : they consti- 

 tute as many centres of radiation 

 of the fine tubes, which, with 

 their uniting clear substance, 

 constitute the dentine. l 



An analogous complexity is 

 produced by numerous fissures, 

 radiating from a central mass of 

 vasodentine, which more or less 

 fills up the pulp cavity of the 

 seemingly simple conical teeth, 

 fig. 245, of the extinct ' Dendro- 

 dont ' fishes. 



A portion of the transverse section, a, fig. 245, magnified, 

 fig. 246, shows the fissures diverging from the pulp-cavity, p, and 

 its reticulate extensions, and sending small branches into the den- 

 tinal lamellae. 



These lateral offsets subdivide into a few short ramifications, 

 like the branches of a shrub, and terminate in irregular and 

 somewhat angular dilatations, simulating leaves, but which resolve 

 themselves into radiating fasciculi of dentinal tubes. There are 



o 



from fifteen to twenty-five or thirty-six of these short and small 

 lateral branches on each side of the main rays. 



Tooth of a Labyrinthodon, natural size ; a line of 

 section, v. 



v. pp. 195217, pi. 64A, 64B. 



