PROFESSOR OWEN ON THE AYE-AYE. 77 



characters of the locomotive organs in the ordinal grouping of the mammalian class. 

 The fore limbs and hind limbs have the same difference of length, and the same general 

 proportions to the trunk, in Chiromys as in Galago. The fingers of the hand — long, 

 slender, sub-nude, freely divergent from their metacarpal articulations — have also nearly 

 the same proportional length, one to the other, in Chiromys and Galago. The superior 

 length of the fourth finger, which begins, in the descending order of Quadrumana, to 

 be manifested in Ateles, is general in the LemuridcE, Tarsius being an exception, and 

 reaches its maximum in the Aye-aye. The inferior length of the index, slightly 

 manifested in Ateles, is more marked in most Lemuridcs, as it is in Chiromys ; but 

 amongst the slow Lemurs it is carried to the extent of malformation, as, e. g., in 

 Perodicticus. 



Although in many Rodents, and especially in the Squirrels, the fore toes have consider- 

 able mobility, they are but four in number, the thumb being a mere vestige : they are 

 more parallel, in their usual position ; they are shorter in proportion to the hand or limb, 

 are thicker, and more hirsute. The pollex in Chiromys has the same degree of opposability 

 as in other Lemuridcs : it is shorter, but thicker than the other fingers, especially at the 

 last segment. The extent of the naked palm is another lemurine or quadrumanous 

 character. The attenuated mid-digit is a curious speciality of the Aye-aye. Even in 

 this, perhaps, may be discerned an affinity to the nocturnal Lemuridas, in which the 

 hand is the seat of other extreme varieties. In Perodicticus, for instance, the index is 

 reduced to its metacarpal, first phalanx, and a vestige of its second phalanx, which 

 forms an unarmed tubercle, as if the finger had been there amputated : in Chiromys 

 the medius seems to be atrophied, though retaining its length and normal joints. 



The hind feet of Chiromys are strictly ' pedimanous,' while their secondary modifi- 

 cations best accord with the lemurine pattern of the grasping foot. The extent of the 

 naked sole, the long and narrow tarsus, the thick, terminally enlarged thumb, with its 

 flat nail, all proclaim that afiinity ; the difference from other Lemurida being only 

 shown by the more nearly equal length of the four unguiculate toes. 



The Aye-aye has a pair of nipples situated one on each side the umbilicus, but on a 

 rather lower level, as in the Tarsier ; but there is no trace of a pectoral pair in addition 

 to the ventral pair. The Rodents have three or more pairs of nipples. 



Even in regard to the dentition, some very significant approximations to the Rodent- 

 like type in Chiromys are offered by the LemuridcE among the Quadrumana. Thus, in 

 the Indris (Lichanotus) the lower incisors are reduced to a single pair ; and, of the two 

 pairs above, the anterior pair is the longest. In the Tarsiers, also, where a single pair of 

 lower incisors is opposed to two pairs above, the foremost of them is conspicuously the 

 longest, even longer than the canine. In Propithecus diadema, Bennett, the first incisor 

 much exceeds the lateral one in size. 



The well-marked division of the upper incisor of the Aye-aye into an anterior 

 thicker enamelled portion and a posterior suddenly narrow portion, might suggest 



