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Show 1897.] MEILAGASY GENUS RRACHYUROMYS. 699 examination shows that the Rhlzomyes (Tachyoryctes, Rhizomys) and Brachyuromys are nearly related to each other-the same holds good, in a somewhat minor degree, with regard to Spalax and Siphneus. The Rhlzomyes are highly adapted to fossorial habits ; Brachyuromys much less. The molars of both will be considered below. The skull of the two (Rhlzomyes and Brachyuromys) presents the following agreements, B. ramirohitra being somewhat intermediate between Tachyoryctes and B. betsileoensis, although standing of course closer to the latter:- (1) The zygomata diverge outwards posteriorly, more in Rhlzomyes than in Brachyuromys ; the malar process of the squamosal parts at right angles from the skull and is strongly developed. (2) The jugal is very strong and approaches closer to the lachrymal than in other Muridae. (3) The infraorbital foramen in Brachyuromys is situated higher above the molar series and reaches higher up than in other Muridae; the narrowed lower portion being lower and wider in B. ramlrohltra. In Tachyoryctes it is located higher still, and there is almost no narrowed passage below. In Rhizomys the foramen is situated higher still, and much shortened as well as broadened. (4) The skulls of both Rhlzomyes and Brachyuromys are depressed and massive. (5) Mandibulae short, massive and high. Anterior margin of coronoid process almost vertical. (6) The lower maxillary border, between premaxillary suture and first molar, viewed in profile, appears higher anteriorly, sloping down backwards towards the anterior alveolar border. (7) The molar series diverge backwards. (8) The glenoid fossa is, outside and inside, delimited by longitudinal parallel crests. (9) The anterior margin of the nasals does not reach as much forwards as that of the premaxillaries. The skull of Rhlzomyes differs from Brachyuromys in the following characters, which are all of them the expression of the higher fossorial adaptation and the more hypselodont molars :- Eyes and ears very small; tail very short. A sagittal crest. Increase in vertical extent of the maxilla, upwards as well as downwards.-Anterior narial aperture depressed and broad.-Foramina incisiva small and situated backwards, being overgrown by the premaxillaries. The upper posterior processes of the premaxillaries extend also far backwards.- The distance between m.l and anterior extremity of the premaxdlaries, depending on the increased length of the incisor alveoli, is much increased as well.-Viewed in profile, the sloping backwards of the inferior border of premaxillary and maxillary, between the incisors and first molar, is much steeper than in Brachyuromys.-The great horizontal extension of the lower incisors and the great vertical extension of the lower molars |