goid muscles. Same specimen shown in Fig.
1. x 2.]

The muscle was probably divided into a major medial mass, the temporal,
and a lesser, sheetlike lateral mass, the masseter. The temporal was
the largest of the adductors and arose from the lateral parts of the
parietal, the dorsal parts of the postorbital, the most posterior
extent of the postfrontal, and the upper parts of the squamosal. The
muscle may have been further subdivided, but evidence for subordinate
slips is lacking. The fibers of this mass were nearly vertically
oriented in lateral aspect since the parts of the ramus that are
available for their insertion lie within the anteroposterior extent of
the adductor chamber. In anterior aspect the fibers were obliquely
oriented, since the jaw and subtemporal fossa are lateral to much of
the skull-roof from which the fibers arose.

The masseter probably arose from the quadratojugal, the jugal, and
ventral parts of the squamosal, although scars on the quadratojugal and
jugal are lacking. The squamosal bears an indistinct, gently curved
ridge, passing upward and forward from the posteroventral corner of the
bone and paralleling the articulation of the squamosal with the
parietal. This ridge presumably marks the upper limits of the origin of
the masseter from the squamosal.

[Illustration: FIG. 3. _Captorhinus._ Cross-section of right half of
skull immediately behind the pterygoid flange, showing masseter,
temporal, and anterior pterygoid muscles. Same specimen shown in Fig.
1. x 2.]

[Illustration: FIG. 4. _Captorhinus._ Internal aspect of left
mandibular fragment, showing insertion of posterior pterygoid muscle.
KU 8963, Richard's Spur, Oklahoma. x 2.8.]

The masseter inserted on the external surface of the coronoid process,
within two shallow concavities separated by an oblique ridge. The
concavities and ridge may indicate that the muscle was divided into two
sheets. If so, the anterior component was wedge-shaped in
cross-section, and its thin posterior edge overlapped the larger mass
that inserted on the posterior half of the coronoid process.

From a functional standpoint it is doubtful that a major component of
the adductors arose from the quadrate wing of the pterygoid, for when
the jaw is closed the Meckelian fossa is directly lateral to that bone.
If the jaw were at almost any angle but maximum depression, the
greatest component of force would be mediad, pulling the rami together
and not upward. The m