riorly and curves
slightly in a dorsal direction and meets the Meckelian fossa. The
curved part of the ridge is made of the prearticular bone alone. A
small hollow above the ridge, anterior to the glenoid cavity, faces the
medial plane of the skull and is bordered by the articular bone behind
and above, and by the Meckelian fossa in front.

The surfaces of the hollow and the prearticular-articular ridge bear
tiny grooves and ridges that seem to be muscle scars. The entire area
of the hollow and its bordering features was probably the area of
insertion of the posterior pterygoid.

However, the area of insertion lies mostly ventral to the articulating
surface of the articular bone and extends but slightly in front of it.
Seemingly little lever effect could be exercised by an adductor
attaching in this position, namely, at the level of the fulcrum of the
mandibular ramus.

The posterior pterygoid muscle probably arose from the anterior portion
of the pterygoid wing of the quadrate, from a ridge on the ventromedial
surface. From the relationship of the muscle to the articulation of the
jaw with the skull, it may be deduced that the muscle was limited in
function to the stabilization of the quadrate-articular joint by
keeping the articular surfaces in close contact with each other and by
preventing lateral slipping.

Finally there is evidence for an adductor between the temporal and
masseter masses. The anterior dorsal lip of the Meckelian fossa
supports a small knob to which this muscle attached, much as in
_Sphenodon_ (Romer, 1956:18, Fig. 12). Presumably the muscle was
sheetlike and attached to the skull roof, medial to the attachment of
the masseter.

A pseudotemporal may have been present, but evidence to indicate its
extent and position is lacking. The muscle usually arises from the
epipterygoid and nearby areas of the braincase and skull roof and
inserts in the anterior parts of the fossa of the jaw. In _Captorhinus_
the lateral wing of the pterygoid cuts across the fossa, effectively
blocking it from the upper and medial parts of the skull, the areas of
origin for the pseudotemporal.

Dimetrodon

The morphology of the skull of _Dimetrodon_ closely resembles that of
the primitive _Haptodus_ (Haptodontinae, Sphenacodontidae), and "hence
may be rather confidently described as that of the family as a whole"
(Romer and Price, 1940:285). The major differences between the two
genera are in the increased speciali