. Monographs of North American rodentia [microform]. Rodentia; Paleontology; Rongeurs; Paléontologie. i i'- ,i ;i ',i^i' \ '«! ! j|i it I'f ) ' i'T 1 ii If. 568 MONOOIiAPHS OF NORTH AMEBIOAN BODENTIA. plane lengthwise, but much arched in the opposite direction. To the outer side of the glenoid fossae, the zygomata form a broad flat expansion or horizontal plate, which widely separates the ends of the malars from each other, and largely increases the zygomatic width of the skull, so conspicuous in this species. Nothing of the sort is seen in Arctomys, Sciurus, etc., where the zygomatic process
. Monographs of North American rodentia [microform]. Rodentia; Paleontology; Rongeurs; Paléontologie. i i'- ,i ;i ',i^i' \ '«! ! j|i it I'f ) ' i'T 1 ii If. 568 MONOOIiAPHS OF NORTH AMEBIOAN BODENTIA. plane lengthwise, but much arched in the opposite direction. To the outer side of the glenoid fossae, the zygomata form a broad flat expansion or horizontal plate, which widely separates the ends of the malars from each other, and largely increases the zygomatic width of the skull, so conspicuous in this species. Nothing of the sort is seen in Arctomys, Sciurus, etc., where the zygomatic process of the squamosal bends downward from the outer border of the glenoid; while, in Haplodon, it forms a broad horizontal shelf for articulation to the malar (f). At any rate, the broad plate is there, but how much of it is squamosal and how niuch is malar, the obliterutiun of the suture prevents me from determining. The occipital view of the skull is flat, more or less perpendicular, though, especially in younger skulls with decided forward-upward obliquity, two or more times as wide as high, with the general contour of a low isosceles triangle. The straightness of the basal line is chiefly broken by the downward projec- tion of well-developed paroccipital processes; the upper outline curves as already described, in speaking of the superior view of the skulls. The general surface is a|>proximately plane as well as perpendicular, though appearing depressed at the sides, owing to the projecting of the flange-like occipital ridge. A considerable portion of the back walls of the bullae auditorise appears upon this plane of the skull, as irregularly quadrilateral plates bounded exteriorly by the mastoids, interiorly by the paroccipitals, and them^lves forming a part of the superior border of the occipital plane on each side. The foramen magnum appears mostly in the plane of the occiput, its lower margin merely making a shallow emargination of the base of the skull (more con- spicu
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Keywords: ., bookcentury1800, bookdecade1870, bookpub, booksubjectpaleontology
