294 THE DENTAL SYSTEM OF THE PRIMATES [SECT. A 



in most instances, and thus the position is diametrically opposed 

 to that of Cope. Forsyth-Major was able to shew however that 

 the history of the teeth of Rodents gives good support to his view, 

 and Tims (op cit. p. 139) confirms this application (of the theory) 

 to Rodentia. 



Considerations of the following kind are adverse to the multi- 

 tubercular theory: (a) Should the "mammalian" claims of the 

 Upper Triassic fossil remains known as Dromatherium 1 (Fig. 204, 

 No. 3) be made good, then the multituberculate forms are coeval 

 with a primitive " triconodont " form of molar tooth. From the 

 latter type it is possible though not probable that the tri- 

 tubercular types are derived, (b) Mammalian embryology shews 

 that the cusps in development first assume a triangular disposition, 

 whereas on the theory of Polybuny a multituberculate stage would 

 be expected 2 . 



In so far as the Primates are concerned, the theory of Multi- 

 tuberculism is not easily applicable. Indeed the molar teeth of 

 the Orang-utan, as well as occasional but not rare anomalous 

 forms of the human molars (especially those of the lower set), 

 suggest that the multitubercular condition may appear suddenly 

 and sporadically. But it is not necessarily atavistic or reversionary, 

 for it may imply adaptation to some special circumstances of 

 nutrition. 



C. The Theory of Concrescence. Another view is that of 

 Tims (op. cit. passim), who was impressed with the fact that the 

 cingulum is capable of throwing up offshoots in the form of cusps. 

 This fact is duly recognized by the exponents of the tritubercular 

 theory both as regards the premolar, and to some extent as regards 

 the molar teeth. Tims proposes to adopt this explanation as 

 regards the premolar teeth, while as regards the molar teeth, and 

 this is an important point, he suggests the concrescence of 

 primarily distinct elements placed originally in an antero-posterior 



1 This extraordinary animal is represented by a mandible, in which three 

 incisors, a canine, three conical premolars, and seven molars are differentiated. 

 The molars bear three conical cusps and are neither multituberculate nor tri- 

 tuberculate. 



2 Osborn, Evolution of Mammalian Molar Teeth, 1907, p. 208, deals in some 

 detail with the theory of multitubereulism. 



