80 PROFESSOR OWEN ON THE AYE-AYE. 



cervical axis in the ordinary position of the head. The alisphenoids do not reach the 

 parietals in Rodentia, but they rise to the height of the squamosals for that purpose in 

 the Aye-aye, as in most Quadrumana. In the Chiromys the bony frame of the orbit is 

 entire ; in the Rodents it is widely incomplete behind ; and, in the species where a 

 postorbital process is present, it ends in a free point. In the complete circumscription of 

 the rim of the bony orbit, Chiromys exemplifies its quadrumanous affinity ; whilst it shows 

 the special family to which in that order it belongs, by the deficiency of the wall par- 

 titioning the orbital from the temporal cavity. The Lemurs, in this defect, indicate 

 the transition to the lower unguiculate Gyrencephala, the Galeopithecus offering the last 

 step by the incompleteness of the orbital frame-ring behind. The outlook of the orbits, 

 obliquely forward, upward, and outward, but least so in the last direction, differs signifi- 

 cantly from the direct outward aspect of those cavities in most Rodents. The paroccipital 

 projects freely in Sciurida and other Rodents ; in some, as in the Capybaraand Coypu, 

 to a great length. The zygomatic part of the squamosal begins in the Aye-aye at the 

 lambdoidal ridge and extends forward ; in Rodents it begins much in advance of that 

 ridge, and inclines downward before bending forward. The malar bone by its width and 

 depth, expanding the orbit by its outer convexity, and uniting behind with the frontal as 

 well as with the squamosal, speaks for the Lemurine and against the Rodent affinities of 

 Chiromys : but, as in other LemuridcB, it does not join the alisphenoid, as it does in higher 

 Quadrumana. The posterior plate of the squamosal is long and narrow in Rodents, 

 clamping the tympanies and mastoids to the sides of the cranium ; no approach to this 

 character is seen in Chiromys. The facial plate of the maxillary in Rodents is either 

 almost used up by a large antorbital vacuity (Anomalurus), or if entire, as in Sciurus, 

 is scooped by a deep vertical channel. In Sciurus bicolor the maxillary as well as the 

 premaxillary joins the broad frontal ; in Anomalurus pelii a larger lacrymal is interposed, 

 as in Chiromys ; but no Rodent shows the lacrymal fossa and foramen on the facial 

 plate, external to the rim of the orbit, as in Chiromys : this is a very significant mark of 

 the close affinity of this genus with the Lemuridce, in which the entry of the lacrymal 

 canal is external to the orbit. The interposition of the premaxillary between the nasal 

 and maxillary is one of the most marked differences in the skull between Chiromys and 

 other Quadrumana ; its agreement in this respect with Rodents depends upon the 

 anomalous development of the incisors. The nasal septum is continued almost to the 

 hinder opening of the nasal passages in Chiromys as in Lemuridce, but is far from reaching 

 that orifice in the SciurideB. The pterygoid processes of the alisphenoid show no trace, 

 in Chiromys, of the canal for the ectocarotid, so general in Sciuridcs and other families 

 of Rodentia. 



Viewing the Aye-aye as among the lowest forms of Quadrumana, it is interesting 

 to find a reappearance of the frontal sinuses which the highest of that order exhibit, 

 but which are wanting, as a rule, in the intermediate series, from the Apes to the normal 

 LemuridcB inclusive. The maxillary series of sockets converge more or less anteriorly 



