OCR Text |
Show 68 M R. E. R. ALSTON ON THE ORDER GLIRES. [Jan. 18, drical, either covered with scales arranged in rings, or more or less hairy The Myomorpha contains such a variety of forms, many or them much specialized, that it is only by allowing for exceptions that its definition can be carried further ; still many and important distinctions are common to the vast majority. The form of the mandible bv which the section was first separated from the Hystrico-morpha, agrees with the last section, the angular portion springing from the lower edge of the bony covering of the lower incisor, excepting in the subfamily Bathyerginee, in which it has exactly the form so characteristic of the hystricine rodents. The other cranial characters are very varied. In the more typical forms the intraorbital opening has a peculiar shape, which may be termed murine ; it is high, perpendicular, narrow, wider above than below; ana tne lower root of the maxillary zygomatic process is perpendicular and flattened into a thin plate with a rounded anterior edge. 1 he zygoma is comparatively slender; the malar seldom advances far torwaru (except in the Dipodida), and is usually supported below by a continuation backwards of the maxillary process, being reduced in some Fig. 3. Mandible of Bathyergus maritimus. of the typical genera to a mere splint between the latter and the squamosal process. The outer walls of the pterygoid fossae are generally obsolete ; and they have no direct fissure at the bottom, except in the aberrant subfamily named above. The clavicles are perfect except in the Lophiomyidce. |