TEETH. 



les coquilles." And the editor (M. Duvernoy), 

 in order to obviate any possibility of miscon- 

 ception, has himself subjoined a note to that 

 passage, as follows: "^L'ivoire a etc aussi 

 appelle substance osseuse, a cause de son analogic 

 de composition chimique et de durete avec 

 les os. Mais la nature inerte et inorganique 

 de cette substance, mieux appreciee dans ces 

 derniers temps, surtout par les travaux de 

 M. Cuvier, ne permet plus de la designer, avec 

 justesse, par cette seconde expression. Du 

 moins est-il necessaire de premunir le lecteur 

 centre l'ide fausse qu'il pourrait en tirer, 

 qu'elle serait organisee, qu'elle se develop- 

 perait a la maniere des os." Tom. cit. p. 201, 

 (1836). In the same spirit in which M. Du- 

 vernoy sees (in 1848) that a true idea, instead 

 of a false one, may be drawn fromcasual expres- 

 sions and similies loosely applied in the old Le- 

 cons of 1800 and 1805 ; others have sought to 

 depreciate the val ue of the establishment of the 

 truth by citing the doubts, or tentative approxi- 

 mations made by Purkinje and Schwann to 

 my theory, interpreting such approximations 

 by the light of the established truth. So far 

 from finding such a resting-place for doubt in 

 Cuvier' s early simile, cited by M. Duvernoy 

 in 1848, or in the interrogatories of Schwann, 

 nothing short of the investigation of the whole 

 of this vast subject, zootomically, develop- 

 mentally, and microscopically, as narrated in 

 my " Odontography," sufficed to settle my 

 own doubts ; and nothing short of the evidence 

 and illustrations given in that work appeared 

 to me adequate to convert anatomists from 

 the excretion-hypothesis to the intussuscep- 

 tion theory. 



That the dentine is the ossified pulp is an 

 older notion than that it is an inorganic 

 secretion from such pulp. But an hypo- 

 thesis, to be of any value in science, must be 

 proved. Almost every true theory has been 

 indicated, with various degrees of approxi- 

 mation, before its final establishment : but he 

 has ever been held, in exact philosophy, to 

 be the author of a theory, by whom it has 

 been first rightly enunciated and satisfactorily 

 established. When time has dissipated the 

 mists of individual or national rivalries and 

 jealousies, the name of the true discoverer is 

 clearly seen by the inextinguishable light of 

 true and impartial history : and to that period 

 I look forward with calm and confident hope. 



I proceed now to briefly point out the 

 leading characteristics of the teeth in the dif- 

 ferent classes of the vertebrate animals. 



Dental System of Fishes. 



The teeth of fishes, whether we study them 

 in regard to their number, form, substance, 

 structure, situation, or mode of attachment, 

 offer a greater and more striking series of 

 varieties than do those of any other class of 

 animals. 



As to number, they range from zero to 

 countless quantities. The Lancelet, the Am- 

 mocete, the Sturgeon, the Paddle-fish, and 

 the whole order of Lophobranchii, are eden- 



873 



tulous. The Myxinoids have a single pointed 

 tooth on the roof of the mouth (fig. 559., ) 

 and two serrated dental plates (b) on the 



fig. 559. 



Mi/xine. (Miiller.) 



tongue. The Tench (fig. 514. Vol. III. p. 979. 

 art. PISCKS)* has a single grinding tooth 

 on the occiput (r), opposed to two denti- 

 gerous pharyngeal jaws below (dd). In the 

 Lepidosiren a single maxillary dental plate 

 (fig. 560., a) is opposed to a single mandibular 



Fig. 560. 



Lepidosiren. 



one (b), and there are two small denticles on 

 the nasal bone (c). In the extinct Sharks 

 with crushing teeth, called Ceratodus and Cte- 

 nodus, the jaws were armed with four teeth, 

 two above and two below.f In the ChmceraB, 

 two mandibular teeth are opposed to four 

 maxillary teeth.J From this low point the 

 number in different fishes is progressively 

 multiplied until, in the Pike, the Siluroids 

 (fig. 561.), and many other fishes, the mouth 

 becomes crowded with countless teeth. 



With respect to form, I may first observe, 

 that as organised beings withdraw themselves 

 more and more, in their ascent in the scale of 

 life, from the influence of the general polarising 

 forces, so their parts progressively deviate 

 from geometrical figures : it is only, therefore, 

 in the lowest vertebrated class that we find 

 teeth in the form of perfect cubes, and of 

 prisms or plates with three sides (Myletcs), 

 four sides (Scarus), five or six sides, Mylio- 

 bates (fig. 562.). The cone is the most com- 

 mon form in fishes : such teeth may be slender, 

 sharp-pointed, and so minute, numerous, and 

 closely aggregated, as to resemble the plush 

 or pHe of velvet ; these are called " villifonn 

 teeth" (denies villiformes, dents en velours ) 

 all the teeth of the Perch are of this kind : 



* And Odontography, pi. 57. fq. 5. 



t See Odontography, pi. 22, fas. 2. 6, 7. 



j Ib., pi. 28, figs. 1, 2. 4. 6. 



The French terms are those used by Cuvier 

 and Valenciennes in their great " Histoire des Pois- 

 sons," -Ito. 



