434 



PLAGIAULAX. 



sunied that the correctness of the figures is not questioned. 

 The marsupial nature of the forms is not disputed, nor is 

 there any difference of opinion about the number or desig- 

 nation of the teeth. 



In both species there is a solitary incisor on each side of 

 the lower jaw, hi the fore part of the incisive border, closely 

 followed, without the interposition of a canine, by a series 

 either of three or of four premolars. The rami converge to 

 a narrow point in front, so that the tooth occupies the entire 

 width of the incisive border on each side ; and fig. 13, p. 280, 

 of my former communication, 1 representing the symphy- 

 sial portion endwise, shows (what is confirmed by the other 

 figures) that the two incisors were approximated and colla- 

 teral, as in the rodent type, placental or marsupial. In 

 P. minor (PL XXXIV. fig. 2), the tooth is procumbent. In 

 the other and larger species, P. Bechlesii, it is more robust, 

 with a thicker root, and with a more decided curvature up- 

 wards, suggesting, at the first sight, some resemblance to 

 the form of a canine. In both species the point is bevelled ; 2 

 and I failed to observe in either any mark of the play of an 

 opposed upper tooth. 



What was the function of these incisors? Professor 

 Owen's opinion is expressed thus : ' The large front tooth of 

 Plagiaulax is formed to pierce, retain, and kill.' This con- 

 clusion arrived at, the other characters are naturally regarded 

 in unison with it, until the genus is finally presented to us as 

 a predaceous carnivore. It is therefore necessary to examine 

 the evidence closely. Now, in solving a question of this kind, 

 comparative anatomy supplies for our guidance fundamental 

 principles, which govern the interpretation of mere form. 

 Let us revert to the known marsupial genera, and see what 

 light generalized observation upon them throws upon the 

 question. In all the Carnivorous genera and species, fossil 

 or recent, of which the dentition has been accurately deter- 

 mined, there are three or more incisors, followed by a canine, 

 on each side of the jaw, above and below ; and the empiri- 

 cally observed result is consistent with a rational interpreta- 

 tion of the arrangement, hi reference to their food and the 

 means of procuring it. On the other hand, in all the exist- 

 ing strictly phytophagous genera, there is only a solitary 

 incisor (being that next the axis) on either side of the lower 

 jaw, and no canine ; or if, as among the Phalangers, addi- 

 tional teeth are developed, the outer incisors and canine are 



! PL xxxiii. fig. 13 of this volume. — 

 [Ed.] 



2 Not in the sense of being denuded 

 of enamel by wear ; hut the posterior 



surface is flattened near the apex, so as 

 to yield a slightly bevelled point. (Seo 

 antca, p. 417.) 



