. Carnegie Institution of Washington publication. The basisphenoid is quite similar to that of Dimetrodon^ but the anterior pro- cess, the parasphenoidal portion, is much longer and heavier and extends well forward in a straight line instead of being turned upward as a thin vertical plate. This is one of the most primitive characters of the skull. The pterygoids of both sides are preserved in part. The posterior half is present on both sides. There was the same division of the bone into an anterior and pos- terior and an external portion as in Dimetrodon. The anterior portion is largely missin
. Carnegie Institution of Washington publication. The basisphenoid is quite similar to that of Dimetrodon^ but the anterior pro- cess, the parasphenoidal portion, is much longer and heavier and extends well forward in a straight line instead of being turned upward as a thin vertical plate. This is one of the most primitive characters of the skull. The pterygoids of both sides are preserved in part. The posterior half is present on both sides. There was the same division of the bone into an anterior and pos- terior and an external portion as in Dimetrodon. The anterior portion is largely missing, but enough remains to show that it was flat and covered with small teeth. The posterior portion is nearly vertical, but inclined somewhat inward, and the posterior end overlapped and articulated with the inner side of the inner condyle of the quadrate. The external portion stood out at right angles to the other part of the bone, but was far from vertical, slanting backward at a large angle. The outer face of the ex- ternal process abutting against the lower jaw is rugose, but very thin; there are fifteen small teeth arranged in sockets on the lower side. The development of the external process of the pterj'goid from this slanting condition with a thin external face to the perfectly vertical position with the outer face broad and rugose is one of the clearest lines of development in the suborder. There is no trace of the ectopterygoid. The epipterygoid stands in the usual posi- tion on the upper edge of the pterygoid. It is thin with an elongate base parallel to and rest- ing on the upper edge of the pter\-goid. The lower jaws of both sides are represented by fragments, but these can not be fitted together so as to give an accurate estimate of the length. The jaw was much more slender than in Dimetrodon and of less width anteriorly, but was seemingly quite high behind. The articular region was attached to the inner side instead of being terminal in much the same way as in tha
Size: 2446px × 1022px
Photo credit: © Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorcarnegieinstitutionof, bookcentury1900, bookdecade1900
