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 ina 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 Sciuride 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 Lemuride, 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 tympanics 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 peli 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 Lemuride, 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 Lemuride, butis far from reaching 
that orifice in the Sciuride. The pterygoid processes of the alisphenoid show no trace, 
in Chiromys, of the canal for the ectocarotid, so general in Sciuride 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 
Lemuride inclusive. The maxillary series of sockets converge more or less anteriorly 
