NO. 1976. 



TREESHREWS: FAMILY TUPAIID.E—LYOX 



161 



edge of the orbit is placed only a trifle behind the level of the union 

 of olfactory bulb ^vith the cerebrum, whereas in Tupaiinag the pos- 

 terior edge of the orbit is placed very much behind the level of the 

 point of union of olfactory bulb and cerebrum. The general plane 

 of the orbits in PtUocercus looks more to the front of the animal, the 

 plane of each orbit making with the long axis of the skuU an angle of 

 about 40°. In the case of Tupaiinse the orbits look more to the side, 

 each making with the long axis of the skull an angle of about 20°. 

 Other conspicuous features about the skull of PtUocercus are the wide 

 spreading zygomata, temporal fossa larger than orbit, approximately 

 parallel temporal ridges, a better ossified palate and simpler audital 

 buUee; that is, not divided by internal 

 septa, as is frequently the case in the 

 Tupaiinae. The comparatively small 

 antero-extemal segment of the buUa 

 in Tupaia is very much reduced in 

 PtUocercus. At the apex of the orbital 

 ca-sHty in both Tupaia and PtUocercus 

 are two foramina, (1) the optic and 

 (2) sphenoid fissure. In Tupaia, just 

 below and external to these is the 

 foramen rotundum, situated at the 

 base of the external pterygoid plate, 

 communicating with the cranial 

 cavity as weU as with a canal, the 

 alisphenoid, running lengthwise in 

 the base of the external pterygoid 

 plate. In PtUocercus the foramen 

 rotundum is confluent with the 

 sphenoidal fissure. Posterior to the 

 external pterygoid plate in PtUocercus, 

 near the bulla, is a distinct oval fora- 

 men leading into the cranial cavity; 

 this foramen is almost entirely overlapped by the bulla in Tupaia. 



The post orbital constriction in PtUocercus is slightly less than the 

 interorbital, being sunilar in this respect to VrogcUe. In Tupaia the 

 postorbital constriction is greater than the interorbital. The two 

 limbs of the lambdoid crest in PtUocercus do not meet in a back- 

 wardly projecting obtuse angle as in Tupaiinje, but each limb runs up 

 to meet its corresponding temporal ridge. Between the posterior 

 extremities of the temporal ridges the lambdoid exists as a slightly 

 convex (backwardly) ridge. 



The coronoid process of the mandible is relatively larger and wider 

 in. PtUocercus than in Tupaiei. and the notch between the condyle and 

 coronoid shallower. See figure 14, page 160. 

 S0459'—Proc.X.M. vol.45— 13 11 



Fig. 15.— Upper and lower toothbovs of 

 pxilocekcrslo-kticoxtixextis, x 4; cat. 

 No. 112'jll, U.S.X.M., Sembkoxg Ritee, 



JOHOKE, ItALAT PE^^^-SX^,A. 



