Jaw Musculature of the Mourning and White-winged Doves Part 1

Jaw Musculature of the Mourning and White-winged Doves.

by Robert L. Merz.

For some time many investigators have thought that the genus _Zenaida_, which includes the White-winged and Zenaida doves, and the genus _Zenaidura_, which includes the Mourning, Eared, and Socorro doves (Peters, 1937:83-88), are closely related, perhaps more closely than is indicated by separating the several species into two genera. It is the purpose of this paper to report investigations on the musculature of the jaw of doves with the hope that, together with the results of other studies, the relationships of the genera _Zenaida_ and _Zenaidura_ can be elucidated.

METHODS AND MATERIALS

In order to determine in each species the normal pattern of musculature of the jaws, heads of 13 specimens of doves were dissected (all material is in the Museum of Natural History of The University of Kansas): White-winged Doves (_Zenaida asiatica_), 40323, 40324, 40328, 40392, 40393; Zenaida Doves (_Z. aurita_), 40399, 40400; Mourning Doves (_Zenaidura macroura_), 40326, 40394, 40395, 40396, 40397, 40398.

Thirty-seven skulls from the collection of the Museum of Natural History of The University of Kansas and two skulls from the United States National Museum were measured. The measurements are on file in the Library of The University of Kansas in a dissertation deposited there by me in 1963 in partial fulfillment of requirements for the degree of Master of Arts in Zoology. Specimens used were: White-winged Doves, KU 19141, 19142, 19143, 19144, 19145, 19146, 19147, 23138, 23139, 24337, 24339, 24341, 23592, 23593, 24340, 31025, 31276; Mourning Doves, KU 14018, 14781, 15347, 15533, 15547, 15550, 15662, 15778, 15872, 16466, 17782, 17786, 17788, 17795, 19153, 19242, 20321, 21669, 22394, 22715; Eared Doves (_Zenaidura auriculata_), USNM 227496, 318381. Additionally, the skulls of the Zenaida Doves mentioned above were measured. All measurements were made with a dial caliper and read to tenths of a millimeter.

ACKNOWLEDGMENTS

My appreciation is extended to Professor Richard F. Johnston, who advised me during the course of this study, and to Professors A. Byron Leonard and Theodore H. Eaton for critically reading the ma.n.u.script.

I would like also to acknowledge the a.s.sistance of Dr. Robert M. Mengel and Mr. Jon C. Barlow for suggestions on procedure, and Mr. William C.

Stanley, who contributed specimens of Mourning Doves for study. Mr.

Thomas H. Swearingen offered considerable advice on production of drawings and Professor E. Raymond Hall suggested the proper layout of the same and gave editorial a.s.sistance otherwise, as also did Professor Johnston.

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 const.i.tute 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 ma.s.s in the jaw of doves, and because the musculature is weak there are few p.r.o.nounced 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. ma.s.seter 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. ma.s.seter, 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 a.s.sertion 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 h.o.m.ologous 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 pos...o...b..tal process and ventrally by the temporal process. The fibers converge upon a tendon that pa.s.ses beneath the pos...o...b..tal 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).