82 PROFESSOR OWEN ON THE AYE-AYE. 
thorax, for example, the humerus of Chiromys agrees with that shown by Lemur and 
Nycticebus: in Sciwrus 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 Lemuride 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 Lemuride 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 tuberous, 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 andthe Quadrumana. The obturator foramina are 
relatively larger in Rodentia than in Lemuride or in Chiromys. 
The femur, equalling in length the last ten true vertebre, offers, in Chiromys, a pro- 
portion to the trunk more common in Lemuride 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 than 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 Lemuride ; 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 Seiurus, Pteromys, Myoxus, Anomalurus, Helamys, and 
Dipus. Both perforations are wanting in Castor and Arctomys. 
