M. depressor mandibulae superficialis lateralis.—The origin is fleshy from the squamosal region, slightly posteroventral to the origin of M. adductor mandibulae externus superficialis. A thin aponeurosis lies medial to the muscle fibers. The insertion is by means of an aponeurosis that becomes tendonlike along the posteroventrolateral crista and the posteriormost part of the ventral edge of the lower mandible.
M. depressor mandibulae medialis.—The origin is fleshy from the lateral and ventral surfaces of Ligamentum depressor mandibulae. The insertion is fleshy on the posterior surface of the lower mandible, posterodorsal to the insertions of partes superficialis medialis et lateralis (figs. [4], [9], [10], [13] and [14]).
The parts of M. depressor mandibulae are difficult to distinguish from one another because of considerable intermingling of fibers.
M. pseudotemporalis superficialis.—The origin is fleshy from the posterior wall of the orbit, dorsal to the foramen of the trigeminal nerve, lateral to the origin of M. protractor quadrati and medial to M. adductor mandibulae externus profundus. The insertion is by means of an aponeurosis that bifurcates at the point of contact with the mandibular ramus of the trigeminal nerve, which is at the level of the orbital process of the quadrate (except in the Mourning Dove where the division is more anterior), and which inserts as two tendons on the dorsomedial edge of the lower mandible posterior to the insertion of M. pseudotemporalis profundus. The lateral tendon is superficial to the dorsomedial edge of M. adductor mandibulae externus, and converges with the aponeurosis of pars profundus of that muscle and inserts with it on a tubercle near the dorsomedial edge of the mandible anterior to the insertion of M. adductor mandibulae posterior as mentioned before. The anterior half of the medial tendon lies ventral to the lateral edge of M. pseudotemporalis profundus and the mandibular ramus of the trigeminal nerve. All of the fibers of the muscle insert on the posteroventral surface of the aponeurosis before it divides. Part of M. pseudotemporalis profundus also lies ventral to the medial tendon of M. pseudotemporalis superficialis and, in effect, the tendon is imbedded in the substance of M. pseudotemporalis profundus as it proceeds anteriorly. The trigeminal nerve leaves a slight impression on the ventral surface of the muscle near its origin (figs. [1], [3], [11], [13], [14], [15] and [16]).
M. adductor mandibulae posterior.—The origin is fleshy from the anterodorsal and anterior surfaces of the quadrate body, from the anterodorsolateral, medial and anterior surfaces of the orbital process of the quadrate. The muscle also has an origin from the otic process of the quadrate, partly fleshy and partly by a slight aponeurosis. The insertion is fleshy on the dorsal and lateral surfaces of the mandible immediately anterior to 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.