1897.] MALAGASY GENUS BBACKYCliOMTS. 701 



between the two pterygoid fossae, which is reduced to a thin 

 transparent plate. 



In this way is brought about the great depth and spaciousness 

 of the pterygoid fossae. Their roof is covered by an iri'egular 

 network of raised ridges, apparently for the pterygoid interuus, 

 greatly developed as a masticatory muscle. 



A beginning of these conditions we meet with in the Microtince : 

 in Fiber there is in the bony septum a spacious fenestra, situated 

 farther backwards than the small fontanelle which is seen in 

 Tachijori/ctes. The Microtince are somewhat intermediate in this 

 respect between the Rhizomyes and typical bracbyodont Muridse, 

 including -Bra6*%Hrom?/s. In the latter, the height of the basi- 

 sphenoid is not increased; it slopes considerably downwards from 

 before backwards, so that the shallow pterygoid fossae are situated 

 slightly below the level of the inferior surface of the basispheuoid, 

 which broadly separates them. In MicrotincB they are situated 

 somewhat above the level of the basisphenoid. 



Winge, speaking of the BafJvjerr/im, remarks that the strongly 

 developed m. pterygoideus which is inserted alongside the centra 

 of the sphenoidea has transformed the presphenoid into a thiu 

 vertical plated I find that both the presphenoid and basisphe- 

 noid are thus transformed, at least in the genera Bathyergus and 

 Georychus. 



2. Sjxila.r. — Winge places Spalax amongst the Dipodidje ' on 

 account of the form of the infraorbital canal, and for having ra.l of 

 the same size as m.2. He states though, that besides the complete 

 absence of premolars, this genus is in other respects as well on a 

 somewhat higher level than the rest of the DipodidaB. The outer 

 wall of the iufi'aorbital canal is certainly not greatly developed ; 

 and in adult specimens it is besides pushed considerably forwards, 

 whilst at the same time starting almost horizontally from the 

 cranium. The upper maxillary radix of the zygoma, which in 

 Muridae usually forms the roof of the infraorbital canal, is more 

 obliquely extended downwards in Spalax (not much differing from 

 what obtains in Zapun), so that it helps to form the outer wall 

 of the canal. The direction and extension of the walls, of course, 

 shape the form of the canal itself. But with all that, the agree- 

 ment with the Dipodidae is not so considerable, and besides seems 

 to be a secondarily acquired character in Spalax; and this for the 

 following reasons : — 



(1) In younger specimens of Spalax (B.M.), and in some adult, 

 the outer wall of the canal is by no means pushed considerably 

 forwards and neither is it horizontal, but more upright ; as a 

 consequence these specimens approach Siphneus in the form of 

 the canal. 



» ' Gnavere fra Lagoa Santa,' p. 127, and footnote 62, p. 169 : " Den Del af 

 M. pterygoideus interims, der Toxer op paa Sideme af Xilebenskroppene, er 

 nieget stsrk, naar langt frem under Foramen opticum eg bar oixiformet det 

 Ibi-reste Kilebenskrop til en tynd lodret Plade." Footnote (p. 169) : " De paa- 

 gjaldende Muskier ere gjennemgaaede bos Georychus capensis ; Markerue 

 paa Hovedskallen ere de samme bos de andre Sliegter." 



- ' Gnavere fra Lagoa Santa,' pp. 109, 121, 166. 



Pnoc. ZooL. Soc— 1897, No. XLVI. 46 



