Exploration of the Colorado River of the West and Its Tributaries Explored in 1869, 1870, 1871, and 1872, Under the Direction of the Secretary of the Smithsonian Institution.

Page 272, Exploration of the Colorado River

272 EXPLORATION OF THE CANONS OF THE COLORADO. alveolar plate dips down between the front teeth. The maxillary ends anteriorly in the curve just described ; its other boundaries are obscured in adult life. The side is flat; it suddenly rises in a broad, thin, zygomatic plate, flush above with the general level of the top of the skull, there abutting (as shown by a long persistent suture) both with frontal and intermaxillary. This plate stands away nearly at a right angle with the axis of the skull, but very oblique to the other two planes. It circumscribes the orbit anteriorly; is excavated in the lachrymal region ; its upper border is widened to a sharp-edged surface, and slopes gently outward, downward, and backward; its thin under margin rises to nearly meet the upper, finishing the laminar portion, and continuing to the malar bone as an angular process. A lachrymal bone is plainly indicated at the upper back part of the plate, but its extent and relations are not appreciable. The frontal is much contracted, especially across the middle, having a somewhat hourglass-like superior outline, though both ends are angular. In front, it sends a rectangular median process abutting against the nasals, and inclosed between the intermaxillaries, and an acute lateral process on each side, entering a recess between intermaxillary and maxillary. These sutures seem persistent. Behind, the fronto-parietal and fronto-squamosal sutures are commonly obliterated; when appreciable, the bone is seen to unite with the extremely narrow parietals by a directly transverse straight line, and with the squamosals by an oblique line on each side. These sutures persist longer on top of the head than in the orbital region. The malar bone is a mere splint, reduced coincidently with the great extension of the zygomatic spurs of both squamosal and maxillary. It is somewhat clubbed anteriorly and overrides its support; behind, it is itself overlapped.* The parietals, as already hinted, are singularly reduced in this family. In the skull of an old Geomys, the squamo-parietal suture is obscure or inappreciable, and the squamosals appear to meet each other at the above-described ridge on the median line; careful inspection, however, usually reveals a very irregular and much overlapping squamo-parietal suture, defining * Although the zygoma in this family is a good stout arch, this reduction of the malar prepares us for the delicate thread-like condition of the parts in the next family, Saccom$idce.