. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 184 S. W. W1LLISTON. In all the plesiosaurs (Fig. 16) the union of the squamosal with the postorbital has become much reduced, they merely touching each other and approaching the theriodont type, in which the post- orbital has become wholly separated from the squamosal (Fig. 12). The assumption that the prosquamosal or quadratojugal has thrust itself up between the squamosal and the postorbital is gratuitous, without evidence to support it. And, if they have not been thrust upward into this intercalary position, it must be a
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 184 S. W. W1LLISTON. In all the plesiosaurs (Fig. 16) the union of the squamosal with the postorbital has become much reduced, they merely touching each other and approaching the theriodont type, in which the post- orbital has become wholly separated from the squamosal (Fig. 12). The assumption that the prosquamosal or quadratojugal has thrust itself up between the squamosal and the postorbital is gratuitous, without evidence to support it. And, if they have not been thrust upward into this intercalary position, it must be assumed, if the bones are really present, that they form the lower part of the bar, parallel with the squamosal, intercepting the jugal from union with the squamosal. That the jugal may unite with the squamosal, even when the prosquamosal exists as. FIG. 15. Stenometopon, after Boulenger. an independent ossification, is a fact, as is shown by the structure in the cotylosaur skull. Why then is it necessary to assume that these bones, or either of them, are present in the anomondonts and sauropterygians in a fused condition ? It is of course possible that the quadrate has also become a part of the mammalian arch, as has been urged by Dollo, Al- brecht, Baur and others. The extraordinary development of the squamosal bone in the anomodonts and theriodonts has not only crowded out the prosquamosal and quadratojugal, but has also caused the absorption of the quadrate, enclosed between it and ward development than is usually seen in the Cynodontia ; but the difference between the groups is not due to any difference in the nature of the arches, but to a less de- velopment of the quadrate bone in the Theriodontia, which has resulted in a diminu- tion or atrophy of the descending pedicle of the squamosal bone" (Seeley, Phil. Trans., 1894, p. 997.). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration a
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
