868 



TEETH. 



Fig. 550. 



Fig. 551. 



Magnified portion of section of incisor of Horse ; 

 c cement, e enamel, d dentine. 



the tooth, following the sinuous wavings of 

 the lobes of dentine (ef), which diverge from 

 the central pulp-cavity, a. 



The inflected fold of cement c runs straight 

 for about half a line, and then becomes wavy, 

 the waves rapidly increasing in breadth as 

 they recede from the periphery of the tooth ; 

 the first two, three, or four undulations are 

 simple ; then their contour itself becomes 

 broken by smaller or secondary waves ; these 

 become stronger as the fold approaches the 

 centre of the tooth, when it increases in 

 thickness, and finally terminates by a slight 

 dilatation or loop close to the pulp-cavity, 

 from which the free margin of the inflected 

 fold of cement is separated by an extremely 

 thin layer of dentine. The number of the 

 inflected converging folds of dentine is about 

 fifty at the middle of the crown of the tooth 

 figured, but is greater at the base. All the 

 inflected folds of cement at the base of the 

 tooth have the same complicated disposition 

 with increased extent; but, as they approach 

 their termination towards the upper part of 

 the tooth, they also gradually diminish in 

 breadth, and consequently penetrate to a less 

 distance into the substance of the tooth. 

 Hence, in such a section as is delineated 

 (/. 552.), it will be observed that some of the 

 convoluted folds, as those marked cc, extend 

 near to the centre of the tooth ; others, as 

 those marked c', reach only about half-way 

 to the centre ; and those folds, c" ', which, to 

 use a geological expression, are "cropping 



Tooth of a Labyrinthodon, natural size. 



out," penetrate to a very short distance into 

 the dentine, and resemble, in their extent and 



Fig. 552. 



Transverse section of tooth of Labyrinthodon. 

 (Magnified.') 



simplicity, the converging folds of cement in 

 the fangs of the tooth of the Ichthyosnurus. 



The disposition of the dentine is still more 

 complicated than that of the cement. It con- 

 sists of a slender, central, conical column, 

 excavated by a conical pulp-cavity for a cer- 



