TOOTH-GENESIS IIS THE CANID^. 4o.5 



1^1 oi Cyon riitilans and dpm^' of Canis familiar is, a point vvhicli 

 will be referred to subsequeudy. Compace fig. 3 B and Jig. 4 A. 



It may be urged that the first molar and the fourth premolar 

 belong to an entirely different series, and are not in any way 

 comparable. Such an objectiou has, I believe, never been raised 

 by any of the supporters of the Tritubercular theory ; they have 

 always regarded these teeth as tritubercular derivatives (2), and 

 therefore, I think, one is quite justified in attempting to 

 homologize these various cusps. 



If this be allowed, then, I think it must be said that the 

 Protocone of the molars is not represented in the premolars of a 

 form like the Jackal, and that this is still more accentuated in 

 Oyon. Consequently, if we are to interpret the anterior premolars 

 in the light of the fourth of the series of the upper six cheek- 

 teeth, the/bifr premolars would appear to have the all important 

 Protocone wanting. 



From these considerations I cannot but think that the greatest 

 doubt is thrown upon the Tritubercular theory by a careful study 

 of the cusps themselves in the various teeth. 



Microscopical l^xam ination. 



By the discoveries of Elower, Kiikenthal, and others the term 

 Monophvodont, in its strictest sense, has become uselestJ, thoujtjh 

 still employed to designate those animals which have only one 

 functional set of teeth. 



The Marsupials, the Edentates, and the Cetacea have all 

 histological representatives of at leat^t two dentitions. 



In the Dog, indications of three dentitions are to be found, 

 namely, the Milk, Permanent, and Post-permanent ; the last bein^- 

 especially well-marked in the region of the third upper inci.-or 

 of an animal about three weeks old (27). In all the specimens 

 that I have examined, including a foetus as early as the seventh 

 week, I have been unable to find any trace of a Pre-milk 

 dentition. 



Evidences of the Post-permanent dentition have also been 

 adduced by Lecbe (10) and Kiikenthal (8) in the Seal, Edse(21) 

 in Man, and M. E. Woodward (29) in Erinaceus. Three den- 

 titions are thus represented m all the>e animals. The same 

 number is found represented in the Marsupials, but these Leche 

 has rei'erred to a Pre-milk, Milk, and Permanent. He was led 

 thus to regard them Irom the fact of the functional dentition of 



37* 



