TEETH. 



931 



Cuvier affirms that the number of fangs of an 

 elephant's molar depends upon the number 

 of points at which the base of the gelatinous 

 (dentinal) pulp is attached to the bottom of 

 the capsule; and that the interspaces of these 

 attachments constitute the under part of the 

 crown or body of the tooth, the attachments 

 themselves forming the first beginnings of the 

 fangs. True to his hypothesis of the forma- 

 tion of the dental tissues by excretion, he 

 says * that the elongation of the fangs is pro- 

 duced by two circumstances : first, the pro- 

 gressive elongation of the layers of osseous 

 substance (dentine) which force the tooth to 

 rise and emerge from its socket ; secondly, 

 the thickening of the body of the tooth by the 

 addition of successive layers to its inner sur- 

 face, which, filling up the interior cavity, leaves 

 scarcely room for the gelatinous pulp, and 

 forces it down into the interior of the roots. 



This pulling up of the fang on the one hand, 

 and squeezing down the pulp on the other, are 

 forces too gross and mechanical to be admitted 

 in actual physiology to explain the growth of 

 the root of a tooth or of any other organised 

 product ; such modes of explanation were, 

 however, inevitable in adopting the excretion 

 theory of dental development. 



With regard to the homologies of the com- 

 plex molars of the Proboscidian quadrupeds, 

 a species of insight which may come to be 

 deemed, in the course of anatomical science, 

 as of equal import to the knowledge of the 

 formative processes of parts, I must admit 

 that the mere fact of the marked and dispro- 

 portionate increase of size of the first of the 

 three last molars over its predecessor the last 

 of the first three that are developed may 

 appear but a feeble support to the analogical 

 evidence on which, chiefly, I have classed the 

 three last developed molars of the elephant, in 

 a category distinct from that of their smaller 

 predecessors. But the value of such indica- 

 tion and analogy will begin to be apparent 

 when we examine the condition of dental 

 development in the primeval forms of Pro- 

 boscidians. I have already shown that the 

 typical character of the Diphyodont dentition 

 was more closely and generally adhered to in 

 the genera that existed during the oldest ter- 

 tiary periods in geology than in their actual 

 successors : it became of course highly inter- 

 esting to inquire whether the miocene Mas- 

 todons, the earliest of the great Proboscidian 

 quadrupeds of which we have any cognizance, 

 manifested any analogous closer adhesion to 

 type than their elephantine successors, and 

 whether they would afford any actual proof 

 of the true deciduous nature of the first, 



* " Ces racines et les pedicules qui leur servent de 

 noyaux s'alongent ensuite par deux raisons : d'abord 

 les progres des lames de substance osseuse qui, s'alon- 

 geant toujours, forcent la dent a s'elever et a sortir 

 de 1'alveole ; ensuite Pe'paississement du corps de la 

 dent par la formation des couches successives qui, 

 en remplissant le vide inte'rieur, n'y laissent presque 

 plus de place pour le noyau gelatineux, et le refoulunt 

 vers 1'interieur des tubes des racines." Annnles du 

 Museum, viii. 1807, p. 108 ; Osseui. Fossiles, 1834, 

 p. 527. 



second, or third molars, by the development 

 of a vertical successor or premolar. Cuvier 

 first ascertained the fact, though without ap- 

 preciating its full significance, in a specimen 

 of the upper jaw of the Mastodon angustidetix 

 from Dax, in which the second six-lobed 

 deciduous molar was displaced by a four- 

 lobed or quadricuspid premolar developed 

 above it and succeeding it vertically.* The 

 same important fact was subsequently con- 

 firmed by Dr. Kaup in observations of the 

 Mastodon longirostris of the miocene tertiary 

 deposits of Eppelsheim.f 



This satisfactorily proves the true deci- 

 duous character of the first and second molars ; 

 and that the third molar in order of appear- 

 ance J, is also one (the last) of the de- 

 ciduous series, is indicated by the contrasted 

 superiority of size of the ante-penultimate 

 tooth, which I regard as the first of the true 

 molar series. 



The great extent and activity of the pro- 

 cesses of dental development required for the 

 preparation of the large and complex true 

 molar teeth would seem to exhaust the power, 

 which, in ordinary Pachyderms, is expended in 

 developing the vertical successors of the deci- 

 duous teeth. In the primeval Mastodons above 

 cited, this normal exercise of the reproductive 

 force was not, however, wholly exhausted, anil 

 one premolar, of more simple form than its 

 deciduous predecessor, was developed on each 

 side of both jaws. But even this trace of ad- 

 herence to the archetypal dentition is lost in 

 the more modified Proboscidians of the pre- 

 sent day. 



Another and very interesting mark of adhe- 

 sion to the archetype is shown by the deve- 

 lopment of two incisors in the lower jaw in 

 the young of some of the Mastodons, by the 

 retention and development of one of these 

 inferior tusks in the male of the Mastodon 

 giganteus of North America, and by the reten- 

 tion of both in the European Mastodun longi- 

 rostris. No trace of these inferior homotypes 

 of the great premaxillary tusks have been 

 detected in the foetus or young of the existing 

 elephants. 



In the gigantic Dinotherium the upper in- 

 cisors were suppressed, and the two lower 

 incisors were developed into huge tusks, 

 which curved down from the symphvsis of 

 the massive under jaw. Most of the grinders 

 had two transverse ridges on the crown, as in 

 the Tapir ; two deciduous molars, if not three, 

 were succeeded vertically by two premolars, 

 the second of which (p. 4 of the typical series) 

 closely resembles the true molars, as in other 

 Perissodactyles. 



The typical dentition is departed from in 

 the existing Hippopotamus by the early loss 

 of p. 1, and the reduction of the incisors to 



Q 9 



~- in both jaws : in the extinct Hippopota- 

 mus of India p. 1 was longer retained, and the 



* Ossemens Fossiles, 4to. ; Divers Mastodontes, 

 pi. iii. jffy. 2. 



t Ossemens Fossiles de Darmstadt, 1835, pi. 1. 

 j Odontography, pi. 144,,/fy. 11, rf.3 



3 o 2 



