." But, unaccountably, Watson's illustration (1948:830,
Fig. 4) of his reconstruction limits the insertion of the temporal to
the anterior limit of the Meckelian opening and a part of the coronoid
process above it. No muscle is shown entering the Meckelian canal. It
seems more likely that the temporal entered and inserted in the canal
and on its dorsal lips. The masseter inserted lateral to it, over the
peak of the coronoid process, and overlapping onto the dorsalmost
portions of its external face, as Watson has illustrated (Plate I,
middle fig.).

I am in agreement with Watson's reconstruction of the origins for both
the anterior and posterior pterygoid muscles. On a functional basis,
however, I would modify slightly Watson's placement of the insertions
of these muscles. Watson believed that the jaw of _Dimetrodon_ was
capable of anteroposterior sliding. The articular surfaces of the jaws
of _Dimetrodon_ that I have examined indicate that this capability, if
present at all, was surely of a very limited degree, and in no way
comparable to that of _Captorhinus_. The dentition of _Dimetrodon_
further substantiates the movement of the jaw in a simple up and down
direction. The teeth of _Dimetrodon_ are clearly stabbing devices; they
are not modified at all for grinding and the correlative freedom of
movement of the jaw that that function requires in an animal such as
_Edaphosaurus_. Nor are they modified to parallel the teeth of
_Captorhinus_. The latter's diet is less certain, but presumably it was
insectivorous (Romer, 1928). With the requisite difference in levels of
origin and insertion of the anterior pterygoid in _Dimetrodon_ insuring
the application of force throughout the adduction of the jaws, it would
seem that the whole of the insertion should be shifted downward and
outward in the notch. If this change were made in the reconstruction,
the anterior pterygoid would have to be thought of as having arisen by
a tendon from the ridge that Watson has pictured (1948:828, Fig. 3) as
separating his origins for anterior and posterior pterygoids. The
posterior pterygoid, in turn, arose by tendons from the adjoining
lateral ridge and from the pterygoid process of Romer and Price.
Tendinous origins are indicated by the limitations of space in this
area, by the strength of the ridges pictured and reported by Watson,
and by the massiveness of the pterygoid process of Romer and Price.

Discussion

A comparison of the gener