274 Bulletin American Museum of Natural History. [\ol. XXVII, 



cially in their close agreement in the characters of the base of the skull. 

 In both genera the palate is thinly ossified and in Tupaia this thinness 

 causes small irregular vacuities in the hinder part. The true pterygoids 

 end in small backwardly directed processes, which are widely separated 

 from the low, triangular pterygoid processes of the alisphenoid; these are 

 tunneled at the base by the small alisphenoid canal, and the two \^■ings 

 together form on each side a peculiarly short and wide ectopterygoid fossa 

 (Fig. 21). The functional bulla in both genera is formed from the greatly 

 expanded entotympanic, the true tympanic remaining as a delicate ring 

 inside the entrance of the bulla. The tympanic wing of the basisphenoid 

 is slight or absent; the tympanic process of the alisphenoid in Tupaia is 

 much reduced, but in Ptilocercus (Fig. 21, ///. As.) it retains more of the 

 concavity on its posterior side •which is so characteristic of primitive marsu- 

 pials. 



Thus in the constitution and arrangement of the auditory region the 

 Tupaiida?, as observed by all authorities, differ radically from the other 

 Insectivorcs and approach the non-Malagasy Lemurs (Weber, 1904, pp. 

 366, 745). If, as van Kampen suggests (1905, p. 452) the entotympanic 

 represents merely the expanded and secondarily independent tympanic wing 

 of the petrosal, which is seen in many Marsupials and Insectivores, then the 

 difference in the bulla of the Menotyphla and those of the Lipotyphla be- 

 comes a difference of degree rather than of kind. At any rate the difference 

 as it now stands is a great one and im])lies a relatively long period of separa- 

 tion between the Menotyphla and Lipotyphla, an inference which is rein- 

 forced by much testimony from other parts of the organism. 



Differences from the lipotyphlous Insectivores are also evident in the 

 arrangement of the foramina. In Tupaia the optic foramen is so large that 

 only a spicule of bone remains between it and the sphenorbital fissure. In 

 Ptilocercus however it is smaller and well separated from the latter. The 

 foramen rotundum in Tupaia is entirely distinct from the sphenorbital 

 fissm'c and lies below and behind it, whereas in lipotyphlous Insectivores as 

 well as in Ptilocercus the foramen rotundum is confluent with that fissure. 

 The identification of the foramen in question in Tupaia as the rotundum 

 is strengthened by the fact that it is continuous internally with a groove 

 which has the position of the Gasserian fossa (for nerve Y.^). The foramen 

 ovale is almost hidden beneath the expanded bulla. 



As in other Insectivores and primitive Placentals an alisphenoid canal 

 pierces the base of the pterygoid flange of the alisphenoid (cf. Ptilocercus, 

 Fig. 21, c. al.) and there is a prominent sinus canal on the side of the brain 

 case, opening anteriorly in a supraorbital foramen. 



Lower jaiv. The slender lower jaAV of Tupaia is not distinguished by 



