Development of the Tooth- Rudiments in Rodents. 301 



LIT. — Contributions to the Development of the Tooth- 

 Rudiments in Rodents. Bj Paul Freund *. 



In the autumn of 1890, at the suggestion of Prof. Born, I 

 commenced to investigate the development of the dentition of 

 various Rodents, with a view to discovering whether in the 

 diastema between the fully developed teeth it was still possible 

 to find remains of rudiments of such as had disappeared. It 

 was only after making certain discoveries bearing upon the 

 question that I learnt that a paper by MM. Pouchet and 

 Chabry f contains a series of statements with reference to 

 this subject. Nevertheless, when I have furnished a more 

 precise critical comparison of the results of these authors with 

 my own, it will be seen that what are really very material 

 points have escaped their notice. 



The dentition of the Rodents attracts attention in the first 

 place owing to the great reduction in the number of the 

 teeth. The largest number is found in the Leporidas, which 

 possess twenty-eight teeth, namely i. j, c. q, m. 5, the smallest 

 in the Muridse, in which in the majority of cases the number 

 is sixteen, namely i. ^, c. -^ m, 3 ; Avhile in Hydromys we 

 actually find only twelve teeth (/. {, c. ^, m. -^. The incisors 

 are always separated by a wide diastema from the molars or 

 premolars, as the case may be. As further peculiarities we 

 must regard the absence of the milk-dentition in many species 

 and also the circumstance that the incisors invariably, and 

 the molars usually, belong to the category of continually 

 growing rootless teeth. 



It is assumed by all authors who have written concerning 

 the origin of the Rodents that the latter have been derived 

 from forms with a fuller and, above all, more completely 

 equipped dentition, and that consequently the reduction in 

 the number and the disappearance of certain kinds of teeth, 

 such as the canines, are phenomena of a secondary character, 

 connected with the special adaptation of the dentition to a 

 peculiar sort of food, which could hardly be turned to account 

 without this modification of the teeth. In other words, the 



* Translated from the ' Archiv fiir mikroskopische Anatomie,' Bd. 39, 

 pp. 52.5-554 (Bonn, 1892) : from a separate impression communicated by 

 Dr. Forsyth-Major. 



t G. Pouchet and L. Chabry, '' Contributions a I'Odontologie des 

 Mammiferes," Journal de I'Anatomie et de la Physiologie : Paris, 1884. 



J-nn. (& Mag. N. Hist. Ser. 6. Vol xi. 22 



