PROFESSOR OWEN ON THE AYE-AYE. 8l 



in all Rodents, — least so, perhaps, in Sciurus ; but there is no such convergence in 

 Chiromys. The diastema is chiefly in the maxillary, and is sharp, in Chiromys ; it is 

 chiefly in the premaxillary, and is smooth, broad, and convex, in Fodentia. In this 

 order the squamosal is peculiar for its length, its straight upper border, and the detach- 

 ment of the zygomatic process from the fore part of the outer side ; it forms a deep longi- 

 tudinal groove for the mandibular condyle, and does not anchylose with the petro- 

 tympanic element. None of these characters are shown in the squamosal of the Aye- 

 aye, which conforms with that in the Lemurida, and more especially departs from the 

 Rodent type in the broad flat articular surface for the lower jaw ; but this has no 

 posterior ridge. A well-ossified palate is an exception in the Rodentia, and the Sciurida 

 show best that exception ; but in these the prepalatine or incisive vacuities are longer 

 than in Chiromys, and the postpalatine notch is deeper : in the breadth of the bony palate 

 the Squirrels come nearest to the Aye-aye. 



The mandibular condyle in Chiromys approaches the form of that in Rodentia by the 

 superiority of its fore-and-aft over its transverse diameter ; but, in its oval convexity, 

 it resembles more nearly the condyle in Tarsius than that of any Rodent. In all 

 Rodents the condyle of the mandible is higher than the level of the grinders ; the angle 

 of the jaw is produced backwards beyond it ; the long and narrow coronoid process 

 curves back to nearly the same vertical line with the condyle. The symphysis reaches 

 the lower border of the ramus, and the curved incisive socket projects more or less from 

 the inner surface. All these Rodent characteristics of the mandible are wanting in 

 Chiromys. In certain Lemurida {Stenops, Lichanotus, Illig., Propithecus, Bntt.) the angle 

 of the jaw is rounded ofi" ; but it is nearly on a vertical line with the condyle : its 

 advanced position in Chiromys is a speciality in the Quadrumanous series. It is one 

 which leads it still further from the Carnivora; and the sessile condyle contrasts 

 strongly with the pedunculate one, especially in the small extinct Ferines (Plagiaulax 

 and Triconodon) of the Purbeck beds : a concomitant difference being shown in the den- 

 tition : trenchant teeth, grooved as in the lower carnassials of Thylacoleo, hold the place 

 of the thick flat-crowned molars of Chiromys. 



The scapula of Chiromys diflfers from that of Rodents, and resembles that of Lemurs, in 

 the proportions of the supra- and infra-spinal fossae. The subscapular surface does 

 not show the intermuscular cristse which are usually so well marked in Rodents. The 

 lower border, though well everted, has less the character of a second spine than it shows 

 in the Squirrels. 



The perforation above the internal condyle of the humerus is the rule in the LemuridcB ; 

 it is the exception in the Rodentia. The perforation between the condyles is common 

 in the Rodentia' ; it is not present in the Lemurida. In the foregoing comparison the 

 humerus of Chiromys agrees with that in the Lemurida. In its relative length to the 



' The intercondyloid perforation, without the supracondyloid one, occurs in Leporida, Capybara, Cavia, Doli- 

 chotis, Chinchilla, Lagotis, Myopotamus, Ccelogenys, Dasyprocta, Hystrix, and Arvicola. The supracondyloid 



VOL. V. PART 11. 



M 



