MYOLOGY
The jaw musculature of doves is not an imposing system. The eating habits impose no considerable stress on the muscles; the mandibles are not used for crushing seeds, spearing, drilling, gaping, or probing as are the mandibles of many other kinds of birds. Doves use their mandibles to procure loose seeds and grains, which constitute the major part of their diet (Leopold, 1943; Kiel and Harris, 1956: 377; Knappen, 1938; Jackson, 1941), and to gather twigs for construction of nests. Both activities require but limited gripping action of mandibles. The crushing habit of a bird such as the Hawfinch (Coccothraustes coccothraustes), on the other hand, involves extremely powerful gripping (see, for example, Sims, 1955); the contrast is apparent in the development of the jaw musculature in the two types. Consequently, it is not surprising to find a relatively weak muscle mass in the jaw of doves, and because the musculature is weak there are few pronounced osseous fossae, cristae and tubercles. As a result, the bones, in addition to being small in absolute size, are relatively weaker when compared to skulls of birds having more distinctive feeding habits which require more powerful musculature.
The jaw muscles of the species dissected for this study are, in gross form, nearly identical from one species to another. Thus, a description of the pertinent myology of each species is unnecessary; one basic description is hereby furnished, with remarks on the variability observed between the species.
The terminology adopted by me for the jaw musculature is in boldfaced italic type. Synonyms are in italic type and are the names most often used by several other writers.
M. pterygoideus ventralis: part of Mm. pterygoidei, Gadow, 1891:323-325, table 26, figs. 1, 2, 3 and 4, and table 27, fig. 3—part of M. pterygoideus internus, Shufeldt, 1890:20, figs. 3, 5, 6, 7 and 11—part of M. adductor mandibulae internus, Edgeworth, 1935:58, figs. 605c and 607—part of M. pterygoideus anterior, Adams, 1919:101, pl. 8, figs. 2 and 3.
M. pterygoideus dorsalis: part of Mm. pterygoidei, Gadow, 1891:323-325, table 26, fig. 7 and table 27, figs. 1 and 3—part of M. pterygoideus internus, Shufeldt, 1890:20—part of M. adductor mandibulae internus, Edgeworth, 1935:58, fig. 605c—? part of M. pterygoideus anterior, Adams, 1919:101, pl. 8, figs. 2 and 3.
M. adductor mandibulae externus: a) pars superficialis: parts 1 and 2 of M. temporalis, Gadow, 1891:320-321—part of M. temporal, Shufeldt, 1890:16, figs. 5 and 7—part of M. adductor mandibulae externus, Edgeworth, 1935:58-60—M. capiti-mandibularis medius and profundus, Adams, 1919:101, pl. 8, fig. 1.
b) pars medialis: ? parts 1, 2 and 3 of M. temporalis, Gadow, 1891:320-322—part of M. masseter and ? part of M. temporal, Shufeldt, 1890:16-18, figs. 5, 6, 7 and 11—part of M. adductor mandibulae externus, Edgeworth, 1935:58-60—M. capiti-mandibularis superficialis, first part, Adams, 1919:100-101, pl. 8, fig. 1.
c) pars profundus: part 2 of M. temporalis, Gadow, 1891:321, table 27, fig. 2—part of M. temporal and ? part of M. masseter, Shufeldt, 1890:16-18—part of M. adductor mandibulae externus, Edgeworth, 1935:58-60—? part of M. capiti-mandibularis medius and all of pars superficialis, second part, Adams, 1919:100-101.
M. pseudotemporalis profundus: M. quadrato-maxillaris, Gadow, 1891:322-323—M. pterygoideus externus, Shufeldt, 1890:20-21, figs. 3, 5 and 11—part of M. adductor mandibulae medius, Edgeworth, 1935:58-59—? part of M. pterygoideus posterior, Adams, 1919:101, pl. 8, figs. 2 and 3.
M. protractor pterygoidei: part 4b of M. temporalis, Gadow, 1891: 322-323, table 27, fig. 4—part of M. entotympanious, Shufeldt, 1890:19-20, figs. 3 and 11—part of M. spheno-pterygo-quadratus, Edgeworth, 1935:57.
M. depressor mandibulae: M. digastricus s. depressor mandibulae, Gadow, 1891:318-319—M. biventer maxillae, Shufeldt, 1890:18-19, figs. 3, 4, 5, 6, 7 and 11.
M. pseudotemporalis superficialis: M. spheno-maxillaris, Gadow, 1891:323—part of M. temporal, Shufeldt, 1890:16—part of M. pseudotemporalis, Hofer, 1950:468-477—part of M. adductor mandibulae medius, Edgeworth, 1935:277.
M. adductor mandibulae posterior: ? part of M. temporal, Shufeldt, 1890:16—part of M. adductor mandibulae medius, Edgeworth, 1935:58-59—? part of M. pterygoideus posterior, Adams, 1919:101, pl. 8, figs. 2 and 3.
M. protractor quadrati: part 4a of M. temporalis, Gadow, 1891:322-323, table 27, fig. 4—part of M. entotympanicus, Shufeldt, 1890:19-20, figs. 3 and 11—part of M. spheno-pterygo-quadratus, Edgeworth, 1935:57.
The terminology adopted by me is that of Lakjar (1926) except that the divisions of M. depressor mandibulae are designated by the Latinized equivalents of the names used by Rooth (1953:261-262).
M. pterygoideus ventralis lateralis.—The origin is fleshy and by aponeurosis on the ventral side of the palatine anterior to the palatine fossa. The insertion is fleshy on the ventromedial surface of the lower mandible and continues along the anteromedial surface of the internal angular process to its distal tip. A few fibers leave pars lateralis and insert on an aponeurosis which receives also all the fibers of M. pterygoideus dorsalis lateralis. The latter fact may have prompted Rooth (1953:257) to make the statement that the fibers originating on the dorsal part of the palatine inserted more laterally than those originating on the ventral side. Rooth worked with Columba palumbus, the Woodpigeon, and his description concerned M. adductor mandibulae internus pterygoideus, which is composed of Mm. pterygoideus ventralis et dorsalis of Lakjar (1926). His assertion that ventral fibers, that is to say, fibers arising on the ventral surface of the palatine, insert medially does not appear to be completely true for doves.
Aponeuroses cover most of the lower surface of the muscle and one or two nerves extend into the substance of the muscle. The nerves run from the anterior edge of M. pterygoideus dorsalis medialis and farther posteriorly from a separation in the muscle.
M. pterygoideus ventralis medialis.—The origin is by aponeurosis from the ventral surface of the palatine and fleshy from the palatine fossa. The aponeurosis is the same that gives origin to the fibers of pars lateralis. Part of the aponeurosis becomes tendonlike in the middle of M. pterygoideus ventralis and separates its two divisions. The insertion is fleshy on the lower one-third of the anterior surface of the internal angular process of the lower mandible, and by two tendons on the distal tip of that process. Many of the fibers of pars medialis insert on the tendons. The fibers at their insertion are not distinctly separate from those of pars lateralis and there is considerable mingling of the fibers. Consequently, the medial part of M. pterygoideus ventralis cannot be removed as a part distinct from the lateral part (figs. [1], [4], [10], [21] and [22]).
Ordinarily M. pterygoideus ventralis does not cross the ventral edge of the lower mandible, but in one white-wing the muscle was slightly expanded on the right side and it could be seen in lateral view. The homologous muscle in Columba palumbus apparently is consistently visible in lateral view. (See Rooth, 1953, fig. 6.)
M. pterygoideus dorsalis medialis.—The origin is fleshy on the dorsolateral surface of the palatine immediately anterior to the pterygoid and also on the anterior, dorsolateral, posterior and ventromedial surfaces of the pterygoid. The insertion is fleshy on the ventromedial surface of the lower mandible and the anterior surface of the internal angular process immediately dorsal to the insertion of M. pterygoideus ventralis lateralis.
M. pterygoideus dorsalis lateralis.—The origin is fleshy from the dorsolateral surface of the palatine, anterior to the origin of pars medialis and the insertion is by means of an aponeurosis on the medial surface of the lower mandible, lateral to the insertion of M. pterygoideus ventralis lateralis. The aponeurosis crosses the medial side of the insertion of M. pterygoideus dorsalis medialis. The fibers run in a posteroventrolateral direction and insert on the ventromedial side of the aponeurosis (figs. [1], [6], [8], [9], [13]-[22]).
In one individual, a Mourning Dove, the origin of pars lateralis of M. pterygoideus dorsalis extended to the pterygoid. With this one exception the muscle was uniform throughout the several species.
M. adductor mandibulae externus.—This is the most complex muscle in the jaw owing to its system of tendons and aponeuroses. Three divisions of this muscle were described by Lakjar (1926:45-46) and the divisions appear to be distinguishable in the doves, but there is no clear line of demarcation for any of the parts and the following description is based upon my own attempts to delineate the muscle.
M. adductor mandibulae externus superficialis.—The origin is fleshy from the most lateral area of the temporal fossa. Dorsally the origin is bounded by the base of the postorbital process and ventrally by the temporal process. The fibers converge upon a tendon that passes beneath the postorbital ligament and runs anteriorly among the fibers of pars profundus. The insertion is tendinous on the dorsal surface of the lower mandible in common with the dorsal aponeurosis of pars profundus. The insertion is immediately anterior to the ventral aponeurosis of pars profundus near the medial edge of the dorsal surface on a tubercle at the posterior end of the dorsal ridge of the lower mandible.
M. adductor mandibulae externus medialis.—The origin is by a flat, heavy tendon from the temporal process. The tendon is attached almost vertically on the temporal process. It twists approximately 130° as it runs anteriorly, and becomes a thin aponeurosis, which gives rise on its dorsal and ventral surfaces to many fibers that insert in a fan-shaped area on the mandibular fossa. Fibers from the dorsal and dorsomedial sides of the heavy tendon run rostrad and insert on the ventral surface of the dorsal aponeurosis of pars profundus. From the ventral surface the most posterior fibers converge on an aponeurosis that inserts on a transverse crista on the dorsal surface of the mandible immediately lateral to the ventral aponeurosis of pars profundus and dorsal to the insertion of M. adductor mandibulae posterior. The more anterior fibers insert fleshily on the mandibular fossa. The tendon of origin is actually one with the ventral aponeurosis of pars profundus, which is situated in a horizontal plane. The insertion is primarily a fleshy attachment on the mandibular fossa. Some of the fibers that arise on the dorsomedial and lateral surfaces of the tendon of origin attach to another tendon, which inserts in the midline of the mandibular fossa on a small tubercle near the anterior end. Also, there is insertion by an aponeurosis anterior to M. adductor mandibular posterior as stated above. Fibers attach to the dorsal and ventral side of the aponeurosis.
M. adductor mandibulae externus profundus.—The origin is fleshy from the medial surface of the temporal fossa, the posterior wall of the orbit and the otic process of the quadrate. The origin is bounded laterally by the origin of pars superficialis and medially by the origin of M. pseudotemporalis superficialis. Ventrally the muscle lies against its own ventral aponeurosis, which originates on the posterior wall of the orbit immediately above the articulation of the otic process of the quadrate, and which also receives many fibers from the surface of the quadrate. The insertion is primarily by means of two aponeuroses. The most dorsal aponeurosis inserts on a tubercle at the posterior tip of the dorsal edge of the mandible. The lateral tendon of M. pseudotemporalis superficialis converges with the aponeurosis. It is superficial and there are no fibers on its dorsal surface. The ventral aponeurosis inserts on a crista immediately below the insertion of the dorsal aponeurosis. It receives fibers on its ventral surface from the otic process of the quadrate, and on its dorsal surface gives rise to fibers that insert on the dorsal aponeurosis (figs. [2], [3], [5], [9], [10], [11], [13]-[18]).
The tendon of insertion of pars medialis of M. adductor mandibulae externus does not become a superficial aponeurosis posteriorly in the Zenaida Dove as it does in the Mourning and White-winged doves.
M. pseudotemporalis profundus.—The origin is fleshy from the medial and partially from the dorsal surface of the lower mandible. The origin is almost completely anterior to and partly dorsal and ventral to the medial (most anterior) insertion of M. pseudotemporalis superficialis. The anterior margin of the origin is at the point where the mandibular ramus of the trigeminal nerve enters the mandible. Posteriorly the origin is bounded by the insertion of M. adductor mandibulae posterior, and ventrally by a ridge that is situated about halfway down the medial side of the mandible. The insertion is by aponeurosis on the tip of the orbital process of the quadrate and fleshily on the anterior surface of the same process. The aponeurosis extends about three-fifths of the distance along the muscle and it is dorsal or superficial to all of the fibers. Many fibers insert on the ventral side of the aponeurosis (figs. [1], [5], [13], [14], [15], [16], [21] and [22]).
This muscle is the most variable of all the jaw muscles. In the Mourning Dove the muscle appears rather slender in dorsal view and in the White-winged Dove has an enlarged lateral belly that gives the appearance of a thicker muscle. In the Zenaida Dove M. pseudotemporalis profundus is intermediate in shape between those of the other two species. This muscle will be discussed in detail later.
M. protractor pterygoidei.—The origin is fleshy from the junction of the sphenoidal rostrum and the interorbital septum. Fibers converge on the pterygoid in anteroventrolateral and posteroventrolateral directions. The posterior edge of the muscle is in contact with M. protractor quadrati with which its fibers mingle. The insertion is fleshy on the posterior surface of the lateral half of the pterygoid to its articulation with the body of the quadrate (figs. [6], [8], [9], [11], [13]-[20]).
M. depressor mandibulae superficialis medialis.—The origin is fleshy from the lateral edge of the basioccipital where the muscle is attached to Ligamentum depressor mandibulae and extends in a lateral direction to a point where the structures involved turn dorsad. The insertion is by fibers and a light aponeurosis on the crista that is situated on the posteroventromedial edge of the lower mandible.
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.