1893.] MB. il. r. WOODWABD ON MAMMALIAN DENTITION. 465 



end oipirf, the tooth itself being situated above the anterior end 

 of pm^, but is in no way connected \vith 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 postei-ior 

 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 being too much 

 modified. 



ITT. — GrENERAL CONSIDEEATIONS. 



We have seen from the above that many of the Macropodidae 

 possess vestiges of the five upper incisors of the Polyprotodonts, 

 and that in two cases, viz. Petrogale penicillata and Macropus 

 giganteus, there are traces of no less than 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 Oldfield 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 being 

 incisors nos. 2, 3, and 5. 



The discoveiy 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 even amongst Eeptiles many Lizards 

 and Crocodiles have the number of teeth in each premaxilla 

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

 Fetrogale, 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 reappeared 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 Macropus giganteus only the late calcification of the func- 

 tional teeth can be 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 which I regard as wanting in the Polyprotodonts is 

 the 5th incisor of Fetrogale, for I have found Avhat appears to be 

 an undeveloped enamel-organ in Perameles, between incisors 4 and 

 5 of that form, and corresponding in position with the large 

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

 Perameles in the Teaching Collection of the Eoyal College of 

 Science there is a curiously elongated tooth, occupying a position 

 intermediate between incisors 4 and 5, both of which are wanting j 



