THE TEETH OF MAMMALS. 



283 



closed (in those allied creatures which have an undoubted 

 upper canine) ; (iii.) because it is cut later than the others 

 (Owen). 



These three reasons are weak, because (i.) form is a 

 veiy unsafe guide to homology, and as to the lateness of its 

 development (iii.), it succeeds to the third incisor, by Pro- 

 fessor Owen's own showing, after about the same lapse of 

 time which separated the eruption of the second and third 



incisors. Moreover, Oreodon, an extinct Ruminant with 

 caniniform teeth, has the eight incisors in the lower jaw in 

 addition to a caniniform tooth, which is the fifth tooth counting 

 from the front. With reference to the relative positions of 

 the upper and lower teeth, determining which is and which 

 is not "the canine," (ii.) no one, looking at the dentition 

 of Oreodon, would be inclined to hesitate which teeth he 

 should call " canines ; " yet the lower caniniform tooth 

 shuts behind the upper, and therefore, according to this 

 test, it is not a true canine. 



In the Lemurs there are similarly eight procumbent teeth 



( ! ) Oreodon Culbertsonii (after Leidy). It will be observed that in the 

 upper jaw the four premolars of the typical mammalian dentition are 

 behind the "canine," but that in the lower jaw the tooth which would 

 fulfil the functions of a canine is the first of these four, and therefore is 

 not the corresponding tooth to the " canine" in the upper jaw. 



