. Bulletin - United States National Museum. Science. 138 XJNITED STATES NATIONAL MUSEUM BULLETIN 2 4 7 backward ventrally and then upward to meet the lateral crest contributed in part by the supraoccipital shield. The squamosal contributes the posterolateral portion of the braincase. Commencing anteriorly at its contact with the pterygoid, the squamosal curves backward, outward, and forward to the extremity of its zygomatic process to constitute the hinder limit of the temporal fossa. A shallow trough on the dorsal surface of the squamosal extends backward from about the level of the anterior
. Bulletin - United States National Museum. Science. 138 XJNITED STATES NATIONAL MUSEUM BULLETIN 2 4 7 backward ventrally and then upward to meet the lateral crest contributed in part by the supraoccipital shield. The squamosal contributes the posterolateral portion of the braincase. Commencing anteriorly at its contact with the pterygoid, the squamosal curves backward, outward, and forward to the extremity of its zygomatic process to constitute the hinder limit of the temporal fossa. A shallow trough on the dorsal surface of the squamosal extends backward from about the level of the anterior face of the postglenoid process to the lambdoid crest. The zygomatic process is slender and is directed obliquely outward and forward. The lambdoidal crest is continued forward on the dorsal surface of the zygomatic process. Except at their extremities the exoccipitals are almost hidden from a dorsal view by the lambdoid crest. The. Figure 55.—Posterior view of skull, USNM 16783, of Diorocetus hiatus. For abbreviations, see figure 53. transverse diameter (330 mm.) of the triangular occipital shield of the larger skull (USNM 23494) at the level of the foramen magnum exceeds the greatest distance (230 mm.) from the dorsal rim of the foramen magnum to the apex. The forward thrust of the hinder elements of the skull has pushed the apex of the supraoccipital sliield to the level of the anterior end of the zygomatic process. The lower portion of the triangular supraoccipital shield is depressed noticeably below the level of its lateral crestlike margins. From a dorsal view the occipital condyles appear relatively small and not protuberant. Posterior viev^?.—The subtriangular occipital shield is constituted by the dorsally attenuated supraoccipital and the relatively small lateral exoccipitals. Ventrally each lambdoid crest (fig. 56) does not quite follow the posterior limit of the corresponding squamosal and turning abruptly upward at about the level of the center of the foramen
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