700 DR. C. 1. I'OUSYTH MAJOR OX TUB [ Juue 1 , 



produce the well-known changes in the shape of the mandibula. — 

 The angnlar process is less curved inwards than in the Malagasy 

 genus. — Occiput inclined forwards. 



Basis cranit. — In Brachyuronij/s we have the conditions normal 

 in Muridae ; the tympanic bones are remarkable for their small 

 size. Rhizomyes : Auditory meatus tubular. The space behind 

 the choanse, whose base is formed by the basisphenoid, is much 

 compressed laterally. Brandt, in his description of the skull of 

 the genus Khizomj/s \ comprehending both Tachyorycfes and 

 Ehizomyes^, \TLiakes a statement apt to be misleading. Heferring 

 apparently to the figure of '■'• Nyctocleptes dehan" {=■ Rhizomys 

 sumatrensis) by Temminck,'' he says : — " Die innern Fliigelfortsatze 

 des Keilbeins divergiren so stark nach aussen, dass hinten, wie bei 

 keiqer andern der bekannten Spalacoiden-Gattungen, eine sehr 

 breite Gaumenrinue entsteht." All depends what extension is 

 given to the term ' Gaumenrinne ' (palatal groove). The internal 

 pterygoid processes in fact diverge much with their inferior borders, 

 so that, as is shown in Temminck's figure, and in PL XXXVIII. 

 fig. 3 of the present paper, they almost completely cover the 

 pterygoid fossae. Upwards, however, they converge very much ; 

 and lastly, in the upper third of their height, they run parallel 

 with each other, so as to delimit a groove — whose bottom (or roof) 

 is occupied by the basisphenoid — -which is very deep anteriorly 

 and whose upper portion is exceedingly narrow (Rh. sinensis). 

 In Rh. sumatrensis the groove is slightly shallower and less narrow ; 

 and the same, although in a minor degree, holds good with regard 

 to Rh. pruinosus. In Tachyorydes the groove in question is less 

 deep ; backwards, where it is no more bordered by the internal 

 pterygoid processes, it appears as a very narrow longitudinal 

 groove in the middle line of the basisphenoid, which is thus parti- 

 tioned in two lateral portions; whereas in Rhizomys it has only 

 somewhat raised borders. Anteriorly, the "palatal groove" 

 appears somewhat deepened and enlarged, as shown in Eiippell's 

 plate'' and in PI. XXXVIII. fig. 3 of the present paper. 



In consequence of the vertical extent of the maxillary in 

 Rhizomys, the bony palate comes to be situated at a very deep level. 

 As a consequence, the external pterygoid processes also acquire a 

 considerable vertical extension, since they serve as a " support for 

 the maxillary." ° But this is not the only explanation of the great 

 depth of the pterygoid fossae ; otherwise their roof — or rather 

 their bottom, as we are speaking of them as ' fossae ' — would remain 

 on a level with the inferior basis of the intervening basisphenoid. 

 In Rhizomys and Tachyorydes the anterior portion of the basi- 

 sphenoid becomes increased in vertical size, forming a septum 



^ J. F. Brandt, " Uiitersucliungen lib. d. craniolng. Entwicklungsstufen d. 

 Nager d. Jetztzeit," Mem. Aead. St. P^tersbourg, [6] is. 7ii. 1855, p. 817. 



- lb. p. 306. 



^ ' Monographies de Mammalogie,' ii. Leiden, 1835, p. 40, pi. xxxiii. fig. 5. 



"* Mus. Senckenberg. iii. Taf. x. fig. 2 c {Ehhomys [Tachyori/ctes] macro- 

 ccphalus). 



\ Winge, Meddel. Naturh. Foren. 1881, p. 40. 



