198 ON THE FOSSIL BONES OF PACHYDERMATOtTS QUADRUPEDS. 



they are not used. One and the same production of the capsule often- 

 times deposits its cortical portion on the upper part of the lamella, 

 though as yet it deposits only enamel on the lower part. 



It also happens that the upper part of the interval of the lamellae is 

 already filled by the cortical part, when the lower part is still sepa- 

 rated : then the lower part of the capsular production is found sepa- 

 rated from the upper, and no longer receives its nourishment, except 

 hy its lateral adhesions with the capsule. 



The deposition of the enamel commences almost with the transuda- 

 tion of the osseous substance, and that of the cortical part follows soon 

 after ; so that the summit of each lamella is terminated in its three 

 substances long before its base, and the neighbouring lamellae are 

 soldered together by their summits, before they are yet hardened at 

 their bases. 



To all we have now said, let us add that these different operations 

 are not executed simultaneously in all the parts of the tooth, but that 

 they take place much sooner before than behind : it will be seen that 

 the anterior lamellae will be already united together at their summits, 

 and even at their bases, when the intermediate lamellae will be still 

 separated from each other, at least at their bases, and when the poste- 

 rior ones will not be even formed, and will present only pointed and 

 distinct horns, which must become the summits of their dentuli' (den- 

 telures.) 



From what we have just said it also follows, that the substances of 

 which the teeth are composed are all formed by excretion and by lay- 

 ers ; that the inner substance in particular has nothing in common 

 with the ordinary bones but its chemical nature, consisting equally 

 of gelatine and phosphate of lime, but that it resembles them 

 neither in its tissue, nor in its mode of deposition, nor in that of 

 growth. Its tissue presents neither cells nor fibres, but merely lamellae 

 inlaid, the one in the other : those who compare it to the diploe of the 

 cranium, and suppose cells to be in it, give a very false idea of it. It 

 is not formed in a primary cartilaginous nucleus, which might be suc- 

 cessively penetrated by earthy molecules : it does not grow by a gene- 

 ral and simultaneous development of all its parts, preserving still the 

 same form : in a word, it is not penetrated either by vessels or nerves. 

 Those who thought that the vessels of the pulpy nucleus pass into the 

 body of the tooth were deceived : and those still more so, who maintain 

 a passage of the vessels of the periosteum of the alveolus into the sub- 

 stance of the roots. There does not pass the least fibril of the pulpy 

 nucleus to the substance called osseous : and the latter is not connected 

 to the remainder of the body, except merely by its mechanical inclosure. 

 Thus, no portion of the tooth is regenerated when it has been removed : 

 and if cleft teeth are again consolidated, it is only because new layers 

 forming within are agglutinated to the external, and the latter to 

 them. 



We shall again see new proofs of all this in treating of the ivory, 

 and we shall there refute the objections derived from diseases of the 

 teeth ; but in the mean time, we must eay that most anatomists have 

 very improperly given the name of osseous substance to the inner sub- 

 stance of the teeth, and that they have designated by that of ostifica- 



