82 PROFESSOR OWEN ON THE AYE-AYE. 



thorax, for example, the humerus of Chiromys agrees with that shown by Lemur and 

 Nycticebus: in Sciurus and most Rodents the humerus is relatively shorter; only 

 in the volant Pteromys and Anomalurus the humerus differs as much, or more, by its 

 greater length, as it does in Galeopithecus, from that in Chiromys. The straight outline of 

 the deltoid ridge in the Aye-aye's humerus is a Lemurine feature : its lower part projects 

 and forms an angle in Sciurus. The configuration of the elbow-joint is more Lemurine 

 than Sciurine in Chiromys. 



The Aye-aye resembles the LemuridcB and Platyrhine Quadrumana in the complexity 

 of its carpal structure, — the ' intermedium,' sometimes described as a dismemberment 

 of the scaphoid, sometimes as that of the magnum, being present, together with the 

 accessory scapho-trapezial sesamoid ; but the scaphoid shows the proportion in respect 

 of length whereby the Lemurides more resemble, than do other Quadrumana, the Car- 

 nivora. The Squirrels (S. bicolor, e. g.) have the intermedium and the accessory sesa- 

 moid ; but the scaphoid and lunare are confluent : other Rodents depart further from 

 the Lemurine type of carpus which Chiromys exemplifies. 



The pelvis of the Chiromys, in the ilio-vertebral and ilio-pubic angles, in the degree of 

 expansion of the fore part of the ilium, in the smoothness of its outer surface, and in 

 the moderate development of the ischial tuberosities, closely accords with the Lemurine 

 type. It strongly departs from the Rodent type in the ilio-pubic angle, which in the 

 Squirrels is 145°, in the Aye-aye 110°. The iliac bones, moreover, in most Rodents are 

 bent outwards at their summits, which are thickened and tuberoas, and the outer surface 

 is bisected by a longitudinal ridge. On the other hand, the ischial tuberosities do not 

 bend out in Rodents, as in Chiromys and the Quadrumana. The obturator foramina are 

 relatively larger in Rodentia than in Lemuridce or in Chiromys. 



The femur, equalling in length the last ten true vertebrae, offers, in Chiromys, a pro- 

 portion to the trunk more common in LemuridcB than in Rodentia. In the Squirrels, 

 for example, the femur is relatively shorter to the trunk, and the ridge for the ecto- 

 gluteus projects as a third trochanter. In most Rodents the lower extremity of the 

 femur is less expanded, comparatively, with the shaft thaa in Chiromys, where the femur 

 closely repeats the proportions and formal characters of that in Lemur proper. 



The tibia, by its near equality of length with the femur, instructively proclaims the 

 quadrumanous nature of Chiromys : in most Rodents, and especially those with long 

 hind limbs, or when these have the same proportion to the trunk as in Chiromys, the 

 leg is longer than the thigh, usually in a well-marked degree. The fibula is more 

 slender in proportion to the tibia in the Squirrels and other Rodents, where it is a 

 distinct bone, than in the Aye-aye and Lemurides ; it is also situated more posteriorly : 

 in most Rodents it anchyloses with the tibia. 



Amongst the pentadactyle Rodents, the Squirrels most resemble the Aye-aye in the 



perforation, without the intercondyloid one, is found in Sciurus, Pteromys, Myoxus, Anomalurus, Helamys, and 

 Dipus. Both perforations are wanting in Castor and Arctomys. 



