302 



ANATOMY OF VERTEBRATES. 



that remarkable condition which a solitary genus (Myrmecobius) 



of existing Marsupials also presents, and which was more abun- 



240 dantly manifested in the 



± 2 extinct Amphitheria and 



Spalacotheria of the Oo- 

 litic period. At least f:f 

 true molars may be as- 

 signed to the Chryso- 

 chlore according to their 

 form — the only charac- 

 ter, in the absence of the 

 known order of their 

 vertical displacement and 

 succession, by which the 

 true and false molars can 

 at present be defined in 

 this species. In the 

 upper jaw, ib. 1, the an- 

 terior large laniariform 

 tooth, and the two suc- 

 ceeding small teeth, are 

 incisors, by virtue of 

 their position in the pre- 

 maxillary bones ; the next small tooth, with a simple compressed 

 tricuspid crown, may be regarded either as a canine or a premolar. 

 The crowns of the true molars are thin plates, narrowed from be- 

 fore backward, with two notches on the working edge, and a longi- 

 tudinal groove along the outer and thicker margin. Another 

 anomaly, more remarkable than that of the shape of the true 

 molars, is their separation from each other by vacant intervals, 

 as in many Reptiles. 



The crowns of the five lower true molars, ib. 2, 2. ..6, are com- 

 pressed antero-posteriorly, but are of unusual length, and have 

 the thicker margin turned inward ; the summit of the outer 

 border is pointed and most prominent ; the inner division is sub- 

 divided into two points. The anterior incisor is small and pro- 

 cumbent ; the second has a larger laniariform crown ; the third 

 is small, and resembles the two premolars which intervene be- 

 tween this and the first large tricuspid molar. The lower molars 

 are separated by wider intervals than those above ; the crowns of 

 the opposing series enter reciprocally the interspaces, and inter- 

 lock ; in mastication, the anterior margin of the lower tooth works 

 upon the posterior margin of the opposite upper tooth. 



Dentition of Chrysochlore, magn. 



1. Upper jaw, b side view, a grinding surface. 



2. Lower jaw, a grinding surface, b side view. 



