TEETH. 



929 



I had the tusk and pulp of the great ele- 

 phant at the Zoological Gardens longitudinally 

 divided, soon after the death of that animal 

 in the summer of 1847. Although the pulp 

 could be easily detached from the inner surface 

 of the pulp-cavity, it was not without a certain 

 resistance, and when the edges of the co- 

 adapted pulp and tooth were examined by a 

 strong lens, the filamentary processes from 

 the outer surface of the pulp could be seen 

 stretching, as they were withdrawn from the 

 dentinal tubes, before they broke. They are 

 so minute that, to the naked eye, the detached 

 surface of the pulp seems to be entire, and 

 Cuvier was thus deceived in concluding that 

 there was no organic connection between the 

 pulp and the ivory.* As the learned professor 

 who has contributed the article " PACHYDER- 

 MATA " adopts Cuvier's description of the 

 formation of the teeth of the elephant by 

 deposition and transudation of the tissues 

 from free surfaces of the formative organs, I 

 have the more valued the rare opportunity of 

 testing and" confirming, by examination of the 

 recent animal, the account of the processes of 

 conversion of those organs into the dental 

 tissues, which I gave in my " Odontouraphy." 



Each molar of the elephant is formed in 

 the interior of a membranous sac the capsule, 

 the form of which partakes of that of the 

 future tooth, being cubical in the first molar, 

 oblong in the last, and rhomboidal in most of 

 the intermediate teeth ; but always decreasing 

 in vertical extent towards its posterior end, 

 and closed at all points, save where it is 

 penetrated by vessels and nerves. It is lodged 

 in an osseous cavity of the same form as itself, 

 and usually in part suspended freely in the 

 maxillary bone ; the bony case being destined 

 to form part of the socket of the tooth. The 

 exterior of the membranous capsule is simple 

 and vascular, as shown at in. 5, fig. 592. ; its 

 internal surface gives attachment to numerous 

 folds or processes, as in most other Ungulate 

 animals. 



The dentinal pulp rises from the bottom of 

 the capsule, or that part which lines the deepest 

 part of the alveolus, in the form of transverse 

 parallel plates extending towards that part of 

 the capsule ready to escape from the socket. 

 Tiiese plates adhere only to the bottom of 

 the capsule ; their opposite extremity is free 

 from all adhesion. This summit is thinner 

 than the base ; it might be termed the edge 

 of the plate: but it is notched, or divided 

 into many digital processes. The tissue of 

 these digitated plates is identical with that of 

 the dentinal pulp of simple Mammalian teeth ; 

 it becomes also highly vascular at the parts 

 where the formation of the dentine is in active 

 progress. 



Processes of the capsule descend from its 

 summit into the interspaces of the dentinal 

 pulp-plates, and consequently resemble them 

 in form ; but they adhere not only by their 



* Annales du Museum, torn. viii. (1806), p. 94. 

 The account is repeated verbatim in the posthumous 

 edition of the " CXs.semens Fossiles," 1836. 



VOL. IV. 



base to the surface of the capsule next the 

 mouth, but also by their lateral margins to 

 the sides of the capsule, and thus resemble 

 partition-walls, confining each plate of the 

 dentinal pulp to its proper chamber ; the 

 margin of the partition opposite its attached 

 base is free in the interspace of the origins of 

 the dentinal pulp plates. The enamel organ, 

 which Cuvier appears to have recognised 

 under the name of the internal layer of the 

 capsule, is distinguishable by its light blue 

 sub- transparent colour and usual microscopic 

 texture, adhering to the free surface of the 

 partitions formed by the true inner layer of 

 the capsule. Although the enamel-pulp be 

 in close contact with the dentinal pulp prior 

 to the commencement of the formation of the 

 tooth, one may readily conceive a vacuity 

 between them, which is continued uninter- 

 ruptedly, in many foldings, between all the 

 gelatinous plates of the dentinal pulp, and the 

 partitions formed by the combined enamel- 

 pulp and the folds of the capsule. According 

 to the excretion-view, this delicate apparatus 

 must have been immediately subjected to the 

 violence of being compressed in the unyielding 

 bony box, by the deposition of the dense 

 matters of the tooth in the hypothetical vacuity 

 between the enamel and dentinal pulps; a 

 process of absorption must have been con- 

 ceived to be set on foot immediately that the 

 altered condition of the gelatinous secreting 

 organs took place ; and, according to Cuvier's 

 hypothesis, the secreting function must be 

 supposed to have proceeded, without any ir- 

 regularity or interruption, while the process 

 of absorption was superinduced in the same 

 part to relieve it from the effects of pressure 

 produced by its own secretion. 



The formation of the dentine commences 

 immediately beneath the membrana propria of 

 the pulp : a part which Cuvier distinctly 

 recognised, and which he accurately traced 

 as preserving its relative situation between 

 the dentine and enamel throughout the whole 

 formation of the dentine, and discernible in 

 the completed tooth " as a very fine greyish 

 line, which separates the enamel from the in 

 ternal substance " or dentine. 



The calcification and conversion of the 

 cells of the dentinal pulp commence as usual 

 at the peripheral parts of the lamelliform pro- 

 cesses furthest from the attached base. It 

 may readily be conceived, therefore, that, at 

 the commencement, there is formed a little 

 cap upon each of the processes into which 

 the edges of the pulp-plates are divided. As 

 the centripetal calcification proceeds the caps 

 are converted into horn-shaped cones ; when 

 it has reached the bottom of the notches of 

 the edge of the pulp-plate all the cones be- 

 come united together into a single transverse 

 plate ; and, the process of conversion having 

 reached the base of the pulp-plate, these plates 

 coalesce to form a common base to the crown 

 of the tooth, which would then present the 

 same eminences and notches that charac- 

 terised the gelatinous pulp, if, during the 

 period of conversion, other substances had 



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