378 Mr. C. Spence Bate on the Dentition 



Thus we have five formulas, expressive of as many separate 

 opinions. It was therefore with satisfaction that the author 

 obtained several specimens of young moles, as by their dissec- 

 tion he has been enabled to clear up the several points of diffi- 

 culty, and establish the homological relations of each individual 

 tooth beyond dispute. 



Having made out and determined the forms and positions of 

 the several teeth, and the relation that they bear, in the adult 

 animal, to each other, the author proceeded to unravel the pro- 

 blem of their homological relation to the teeth in the Mamma- 

 lian order. 



In the placental mammals the largest number of teeth is 

 forty-eight, consisting of three molars, four premolars, one 

 canine, and four incisors, on each side of each jaw. In the 

 European mole we find all present excepting one on each side 

 of each jaw. The great point, therefore, to be determined is, 

 which of the teeth of the permanent series is absent. M. Fred. 

 Cuvier has pronounced it to be- an incisor from the upper jaw 

 and the canine from the lower. Prof. Bell leaves out an incisor 

 from the upper jaw and a molar from the lower ; or, since he 

 classifies the premolars and molars under that of molars, we 

 may say that he omits a premolar from the lower jaw. Prof. 

 De Blainville leaves out a premolar from the series in each jaw. 

 Prof. Owen omits an incisor from each jaw ; and Prof. Blasius, 

 the most recent comparative anatomist who has written on the 

 subject, leaves out an incisor from the upper, and a premolar 

 from the lower jaw ; but this last zoologist diff'ers from all the 

 previous writers in classifying the last premolar in each jaw as 

 belonging to the series of molars. In this arrangement Prof. 

 Blasius has evidently been governed by the form and size of the 

 tooth rather than by its relative connexion with the deciduous 

 teeth or their position in the jaws. Classification based upon 

 such observation is liable to great variation, dependent upon 

 the existing wants of animals, and therefore must possess a 

 shifting character — a condition that must exclude it from scien- 

 tific consideration. The only true classification of the teeth 

 must be based upon their position in the jaws, and the homo- 

 logical relation that they hold to each other and to the teeth of 

 other animals. 



Thus there are only three molar teeth in the placental mam- 

 mals, because there are but three teeth in the range of each jaw 

 that are developed without having been preceded in their posi- 

 tion by deciduous or milk-teeth. Therefore, since the tooth 

 that Prof. Blasius classifies as the most anterior of the molar 

 series is anticipated by a deciduous tooth, it must belong to the 

 premolar, and not the molar series. 



