. Bulletin - United States National Museum. Science. 80 UNITED STATES NATIONAL MUSEUM. length, where a roughened elevation is met. From this point posteriorly the ischia tapers rapidly to the blunt truncated end (fig. 44), which is triangular in cross- section. The height and rugoseness of this elevation on the superior border of the ischium is more pronounced in fully adult specimens. The inferior border presents a thin, sharp edge, except at the transversely expanded distal extremity, which is flattened and has a roughened surface that appears to have been closely appHed to the postpubis. In
. Bulletin - United States National Museum. Science. 80 UNITED STATES NATIONAL MUSEUM. length, where a roughened elevation is met. From this point posteriorly the ischia tapers rapidly to the blunt truncated end (fig. 44), which is triangular in cross- section. The height and rugoseness of this elevation on the superior border of the ischium is more pronounced in fully adult specimens. The inferior border presents a thin, sharp edge, except at the transversely expanded distal extremity, which is flattened and has a roughened surface that appears to have been closely appHed to the postpubis. In the restoration of the pelvis of Stegosaurus (fig. 42), Marsh* has indicated the ischium and postpubis as being in contact along their whole length, but it would appear from the study of specimens in the National Museum collections that there was a longitudinal cleft between them, as in Omosaurus. In plate 80, figure 5, Dinosaurs of North America, Marsh shows the distal third of the ischia as meeting on the median line. The shortness of these bones, in conjunction with the great width of the sacrum, appears to make such a imion impossible, and in an impublished plate of the articulated sacrum they are shown only in contact at their ends. Fur- thermore, none of the seven iscliia in these collections shows inner surfaces adapted to or even suggestive of such a carti- laginous symphysis. It is also noted that in the mounted skeleton of S. ungulatus in the Peabody Museum of Yale University the ends of the ischia are not in juxtaposition (pi. 36). Nopcsa ^ lays particular stress on the cleft between the pubis and iscliium. He says: The longitudinal cleft between the pubis and the ischium, which is present in both species of Omosaurus and our Stegosaurus [S. prisms] is a character found in all primitive Ornithopoda; the clos- ing of this cleft observable in S. ungulatus must, therefore, be regarded as a mark of specialization. In view of what is now known of the manner of articulati
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