522 Opposable Power of the Thumb, 



in this group, the characters of which are so remarkable as 

 to merit a more ample notice. The only known represent- 

 ative of the subfamily in question is the aye-aye, or Cheiro- 

 mys of Madagascar, one of those abnormal forms which we 

 continually find interposed between natural groups, partaking 

 in some measure of the characters of each, without decidedly 

 belonging to either, and separated from both by a breach in 

 the chain of affinities, which, as far as our present knowledge 

 extends, is not filled up by those gradual and successive mo- 

 difications of organisation which unite the generality of natural 

 families. The Cheiromys has been associated by some zoolo- 

 gists with the Rodentia, and by others with the Lemurs, 

 among the Quadrumana; but it really belongs to neither of 

 these groups; and the following considerations will show that 

 its proper place will be found among the Pedimana, in a dis- 

 tinct subfamily, probably interposed between the Simiadae and 

 Didelphidae. I speak hesitatingly upon this subject, because, 

 having never had an opportunity of examining the animal 

 itself, I am acquainted with its characters only at second 

 hand ; but, from the descriptions of Buflfon, Cuvier, and Des- 

 marest, it is manifest that its proper location is somewhere in the 

 present family, and probably between its two principal groups. 

 According to Baron Cuvier, the form and characters of the 

 skull assimilate this animal to the Simire and Simiadae, and 

 it is only in the number and arrangement of the teeth that it 

 bears any relation to the Rodentia : its organs of locomotion 

 and prehension are in all respects those of the Pedimana; and 

 its habits and economy, which chiefly depend upon the modi- 

 fication of these organs, are, no doubt, equally similar. In 

 other respects, even its dental system is not so entirely dissi- 

 milar to that of the Didelphidae, as to be altogether without 

 approximate or intermediate connecting modifications. These 

 are very apparent in the Phalangers and Petaurists, both of 

 which resemble the Rodentia in the absence of canine teeth, 

 and in having the incisors separated from the molars by a 

 vacant space ; for the two false molars which partly occupy 

 this interval are mere rudiments which do not enter into the 

 function of mastication, and which may therefore be over- 

 looked in the present enquiry. Both these genera have, more- 

 over, two incisor teeth only in the lower jaw : and, though they 

 have invariably six in the upper, yet the very superior deve- 

 lopement of the central pair, compared with the lateral, which 

 in some species are not more than half their length, brings 

 them alone into contact with the lower incisors, and thus 

 really makes the Phalangers and Petaurists in some degree 



