1893.] 3IR. M. F. WOODWABD 0:!f MAMMALIAN DENTITIOX. 465 



end oi pm^, the tooth itself being situated above the auterior end 

 of pm\ bat is in no way connected \^-ith the latter. The specimen 

 was, however, too old to show the true origin of this tooth. 



The molars were too advanced to show any indication of their 

 lost predecessors or otherwise. Of course the most posterior 

 molar in the jaw was still very young, but as a matter of fact no 

 traces either of predecessors or of successors have been observed 

 to any but the 1st molar, the rest seemingly beiug too much 

 modified. 



111. — Genebal Considerations. 



"We have seen from the above that many of the Macropodidae 

 possess vestiges of the five upper incisors of the Polyprotodonts, 

 and that in t\yo cases, viz. Pdrouale penicillata and Maoropus 

 gir/anteiis, there are traces of no less thau six of these teeth, the 

 full upper incisor formula being, 1.2.3.4.5.6. That the three 

 adult incisors are the 1st, 4th, and 6th ; this conclusion is at 

 variance with that of Old field Thomas (11, pp. 454 and 457), who 

 shows, in a diagram illustrating the relations between the teeth of 

 the Polyprotodonts and Diprotodonts, that he believes the 

 reduction in the number of the incisors in the latter to have 

 been brought about by a suppression of the two posterior teeth of 

 the former. This interpretation I have shown, by the discovery 

 of vestigial teeth, to be erroneous, the teeth which disappear beiug 

 incisors nos. 2, 3, and 5. 



The discovery of 6 pairs of incisors, although an absolute fact, 

 is in many respects an unfortunate one, as we know of no adult 

 Mammal with so many, and eA^en amongst Eeptiles many Lizards 

 and Crocodiles have the number of teeth in each pi'emaxilla 

 restricted to five. I can only suggest in explanation that in 

 Petrof/ale, where the 3 adult incisors are so slight, and where there 

 is in consequence more room in the premaxilla, the additional 

 incisor, which is only apparently lost in the Polyprotodonts (see 

 ante, p. 456), has reajjpeared as a calcified tooth owing to the 

 greater amount of room in the jaw and the lesser abstraction of 

 growth-energy on account both of the smaller size of the adult 

 teeth and of the very late development of the most posterior 

 incisor. 



In Macropiis fjifjanleus only the late calcification of the func- 

 tional teeth can Ije supposed to account for the presence of so 

 many vestiges, and as a fact we notice, directly these adult teeth 

 begin to calcify, the vestigial ones become reabsorbed. 



The incisor wliich I regard as wanting in the Polyprotodonts is 

 the 5th incisor of Petroijale, for I have found w hat ai)i)ears to be 

 an undeveloped enamel-organ in Pi'i'amclcs, between incisors 4 and 

 5 of that form, and corresponding in position with th<^ hirge 

 diastema of the adult. On one side of the upper jaw of an aduli 

 Perameles in the Teaching Collection of the Royal College of 

 Science there is a curiously elongat(*d tooth, occu])ying a position 

 intermediate bet\\e(;n ineisors 4 and 5, both of which are wautintr; 



