the articulating surface. This muscle also has
extensive insertion on the medial side of the lower mandible dorsal to
the insertion of _M. pterygoideus dorsalis medialis_ and posterior to
the origin of _M. pseudotemporalis profundus_ (figs. 1, 3, 5, 17, 18,
19 and 20).

The fibers of _M. pseudotemporalis profundus_ can be distinguished from
the fibers of _M. adductor mandibulae posterior_ because the
pterygoideus nerve passes between the two (Lakjar, 1926:55). Rooth
(1953:255-256) considers as part of this muscle the ventral aponeurosis
of _pars profundus_ of _M. adductor mandibulae externus_ and all the
fibers ventral to it. But I could not justify the inclusion of that
aponeurosis as part of _M. adductor mandibulae posterior_ in the doves
because none of the fibers of _M. adductor mandibulae posterior_ as I
have described it were attached to that particular aponeurosis.

~_M. protractor quadrati._~--The origin is fleshy from the posterior
wall of the orbit medial to the foramen of the trigeminal nerve and
also medial to the origin of _M. pseudotemporalis superficialis_. The
origin describes an arc in the horizontal plane until it reaches the
interorbital septum and the optic nerve. The insertion is fleshy on the
posteromedial edge of the body of the quadrate and the orbital process
of the quadrate and on the otic process of the quadrate. The muscle
also inserts on the ventromedial surface of the orbital process of the
quadrate and the adjacent area of the body of the quadrate (figs. 5, 7,
9, 11, 13-18).

_M. protractor quadrati_ possesses many fibers that arise from _M.
protractor pterygoidei_. Consequently, it is difficult to determine the
exact extent of the origin or the insertion of either muscle.

ACTION OF JAW MUSCLES

~_M. pterygoideus ventralis._~--Contraction of this muscle retracts the
upper mandible by moving the palatine posteriorly, and simultaneously
adducts the lower mandible.

~_M. pterygoideus dorsalis._~--This muscle functions in essentially the
same manner as _M. pterygoideus ventralis_. The result of having a part
of its origin on the pterygoid as well as on the palatine is to
facilitate retraction of the upper mandible.

~_M. adductor mandibulae._~--This is the chief adductor of the lower
mandible and the muscle functions solely in that capacity. In birds
having great crushing ability, this muscle is much larger and more
powerful and the skull is reinforced behind the quadrate in order t