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APPENDICULAR MYOLOGY OF KIRTLAND'S WARBLER

ANDREW J. BERGER

KIRTLAND'S Warbler (Dendroica kirtlandii) is listed as one of the endangered species in the Red Book of Rare and endangered fish and wildlife of the United States (Goodwin et al., 1966). The total population of this warbler is about 1,000 birds (Mayfield, 1962). Inasmuch as the complete appendicular myology has not previously been described for any member of the family Parulidae, it seems worthwhile to describe and illustrate the myology of the Kirtland's Warbler.

I am indebted to Robert W. Storer and Harrison B. Tordoff of the Uni-

versity of Michigan Museum of Zoology for one adult Kirtland's Warbler, collected in Montmorency County, Michigan, 26 June 1935, by Milton B. Trautman. Four other specimens were birds that I had hand-raised from the nest (Berger, 1966). I also acknowledge my appreciation to Mrs. Barbara Downs, who prepared the final ink drawings.

Dissection under a binocular microscope is essential for the study of the myology of a bird the size of Kirtland's Warbler (approximately 5% inches in length). A few of the wing muscles and the short toe muscles approach the minimum size for description by means of gross dissection, even with magnifications x20 and x30. When studying a specimen of Fregilupus varius (Berger, 1957), I discovered by using histological techniques that M. latissimus dorsi pars posterior and M. abductor digiti IV were rudimentary muscles, consisting of a thin layer of striated fibers in a sheet of fascia. For all practical purposes, such a "muscle" is absent. The presence of rudimentary muscles may, however, be of special interest in certain studies, and the modified technique described by Berger (1956) is useful for making a quick preliminary determination of the presence of muscle fibers in fascia or ligament. The terminology of the muscles in this paper is that used by George and Berger (1966).

MUSCLES OF TIlE WING

M. latlssirnus dorsi.--a. Pars anterior arises by an aponeurosis from the neural spine of the last cervical vertebra and from the anterior tip of the spine of the first dorsal vertebra (Figure 1). The thin fleshy belly enters the arm musculature between the bellies of Mm. scapulotriceps and humerotriceps and inserts as a fleshy band (slightly more than 1 mm wide) on a curved ridge, beginning 2.5 mm distal to the articular head of the humerus. Relative to its relations in many birds, the area of insertion is a considerable distance (1 mm) anterior to the origin of the external head of M. humerotriceps.

b. Pars posterior and pars metapatagialis are absent. c. M. latissimus dorsi dorsocutaneous is a thin band of fleshy fibers, about 0.5 mm

;vide throughout most of its length, but slightly wider at its origin and narrower anteriorly, where it tapers to a tendon. The muscle arises by an aponeurosis from

594 The Auk, 85: 594-616. October, 1968

Oct., 1968] Myology o! Kirtland's Warbler 595

• Tensor patagii longus

Interosseus dorsalis

Oeltoldeus post•r•o

Sortoriu• --• Rhomboideus profundus

, ,Omm , Figure 1. Dorsal view of the superficial wing muscles of Kirtland's Warbler.

the median dorsal ridge of the synsacrum and from the fascia covering M. iliotrochantericus posterior. The belly passes cephalad immediately deep to the skin and lateral to the midline and gives rise to an elastic tendon at about the level of the neural spine of the first dorsal vertebra. The tendon continues cephalad deep to the spinal cervical feather tract and can be traced as far as the skin overlying the occipital region of the skull, where the tendon fans out in the subcutaneous connective tissue.

M. rhomboideus super)•icialis.--The superficial rhomboid muscle arises by an aponeurosis from the spines of the last two cervical and the first three dorsal vertebrae and from the anterior tip of the spine of the fourth dorsal vertebra, as well as from the interspinous ligaments between the spines (Figure 1). The belly is much thicker anteriorly than posteriorly. It inserts by fleshy fibers on the dorsomedial edge of the scapula in approximately its anterior three-fourths (13 mm).

M. rho•nboideus pro)•undus.--The deep rhomboid muscle arises by an aponeurosis from the interspinous ligaments and from the posterior tip of the neural spine of the first dorsal vertebra and from the spines of the next four dorsal vertebrae; the origin is from the anterior tip only of the last dorsal vertebra, deep to the aponeurotic origin of M. sartorius (Figures 1, 2). The fleshy fibers pass outward and backward to insert on the medial surface of the caudal 5 mm only of the scapula; this is, relatively, a small area of insertion for the deep rhomboid muscle.

M. serratus pro/undus.--This is a well-developed complex arising by three fleshy fasciculi from the transverse process of the penultimate cervical vertebra, from the lateral surface of the superior portion of the last cervicodorsal rib, and from the lateral surface of the superior portion of the first true rib; the fasciculus from the first true rib is especially wide (Figure 2). The three fasciculi pass backward, fuse, and insert on the medial surface of the scapula for a distance of about 4 mm, just anterior to the insertion of M. rhomboideus profundus.

M. serratus anterior.--For the size of the bird, M. serratus anterior is a relatively wide (1.5 mm) band of fleshy fibers, which arises by fleshy slips from the lateral surface of the ventral part of the last cervi½odorsal rib and from the first true rib at

596 A•oREW J. B•RCE• [Auk, Vol. 85

Deltoideus minor

• /• Interosseus palmaris Os h ........ pulare• *'•,/Løt ....... dorsi ant .....

Serra us l•t• m• •. •

prof undus• , ,,• •Serro, .... , ..... j•/• •H ..... triceps /•///

•Serratu5 me•apa•agJal15

,Omm

•[•u•e ]. •o•ss] •iew of • deep hye• of win• muscles of

the level of its uncinate process (Figure 2). The two fasciculi fuse to form a single belly, which passes dorsad between the two heads of M. subscapularis and inserts by a broad aponeurosis on the ventral edge of the scapula.

M. serratus posterior.--The muscle arises by means of three fleshy fasciculi from the lateral surfaces of true ribs 2, 3, and 4, inferior to their uncinate processes. The fasciculi fuse to form a common belly; it inserts, by fleshy fibers posteriorly and by an aponeurosis anteriorly, on the ventral edge of the scapula in its caudal 3.5 mm (Figure 2).

M. serratus metapatagialis.--This derreal component arises from the lateral surface of the third true rib, inferior to the origin of the fasciculus of M. serratus posterior (Figure 2). The fibers pass upward and forward to insert into the skin of the humeral feather tract.

M. proscapulohumeralis.--M. proscapulohumeralis is well developed in Kirtland's Warbler (Figure 2). The muscle has a 3 mm-wide fleshy origin from the dorsal- lateral surface of the scapula, posterior to the origin of M. scapulotriceps and dorsal to the origin of the external head of M. subscapularis. The belly passes outward and forward to insert on the humerus between the two heads of M. humerotriceps, distal and a little dorsal to the roedial bar which separates the two parts of the double pneumatic fossa on the proximal end of the humerus.

M. dorsalis scapulae.•M. dorsalis scapulae (Figure 1) arises, posterior to the origin of M. proscapulohumeralis, from most of the lateral and ventral surfaces of the scapula in slightly less than its caudal three-fourths (11 ram). The origin from the lateral surface of the scapula is primarily by fleshy fibers; from the ventral edge it is primarily by an aponeurosis. The muscle inserts on the anconal surface of the bicipital crest of the humerus.

M. subscapularis.--The external head of M. subscapularis arises from the lateral surface and from the ventral edge of the scapula for a distance of about 5 mm, beginning at the caudal border of the glenold cavity (Figure 2). The internal head arises from an area about the same length on the medial surface of the scapula. The two heads fuse on a single, well-developed tendon, which inserts on the internal tuberosity

Oct., 1968] Myology oJ Kirtland's Warbler 597

•- I0 mm • I:•ctc•l $• Figure 3. Ventral view of the superficial wing muscles of Kirtland's Warbler. The

humerocarpal band has been removed in order to show the bellies of Mm. flexor carpi ulnaris and flexor digitorum superficialis.

of the humerus. The tendon of M. subscapularis inserts adjacent to the tendon of M. subcoracoideus, but the two tendons do not fuse.

M. subcoracoideus.--The dorsal head of M. subcoracoideus arises from the medial

surface of the anterior end of the scapula adjacent to its articulation with the apex of the clavicle (Figure 4). The long and well-developed ventral head arises from the roedial sternocoracoidal process of the coracoid, just dorsal to its articulation with the sternum. The two heads fuse at the level of the inferior border of the procoracoid process of the coracoid. The tendon inserts on the internal tuberosity of the humerus adjacent to the tendon of insertion of M. subscapularis.

M. pectoralis.•The pectoralis muscle (pars thoracicus) has an extensive origin: from the ventral half of the carina, from the interosseous membranes in the caudal 8 mm of the body of the sternum, and from an aponeurosis extending dorsad from the lateral margin of the sternum over the superficial surfaces of the last three sternal ribs; from the anterior and lateral surfaces of the clavicle and the adjacent area on the coracoclavicular membrane (Figure 3). The muscle has a typical insertion by fleshy fibers, surrounded by a dense tendinous envelope, on the deltoid crest of the humerus.

a. Pars propatagialis brevis is entirely aponeurotic; it splits off the surface of pars thoracicus near its insertion on the deltoid crest. The apo.neurosis fuses with the distal end of the belly of M. tensor patagii brevis and contributes to the formation of its tendon of insertion.

b. Pars propatagialis longus is a minute, flat, fleshy muscle (about 0.5 mm wide and 1 mm long), which arises from the anteromedial surface of the belly of M. pectoralis a short distance (4 mm) from its insertion on the humerus. The fleshy belly gives rise to a tiny tendon; it passes dorsolaterad to insert on the tendon of M. tensor patagii longus opposite the deltoid crest of the humerus. I did not find M. pectoralis propatagilais longus in one specimen of Kirtland's Warbler.

598 A•DREW J. BERGER [Auk, Vol. 85

So gorm:oid procorocoideos tendo• indici• longus

Figure 4. Ventral view of a deep layer of wing muscles of Kirtland's Warbler.

c. Pars abdominalis is composed of two parts: subcutaneus thoracis and subcutaneus abdominalis (George and Berger, 1966: 311). The entire complex extends from the axilla to the region of the knee in the skin covering the lateral wall of the thorax and abdomen.

The anterior, thoracic, part of the complex is composed of two essentially independent, flat muscular bellies. Both arise from axillary fascia and from the ve.ntral surface of the deep portion of the tendinous envelope surrounding the inserting fibers of M. pectoralis. The anteriormost belly inserts by fleshy fibers into the skin of the axillar portion of the ventral feather tract. The posterior belly tapers to a fine, but discrete, tendon, which passes caudad to fuse with the subcutaneous co.nnective tissue along the anterior surface of the crus.

The posterior, subcutaneus abdominalis, portion of the complex arises by fleshy and aponeurotic fibers from the lateral surface of the abdominal wall at a level about midway between the vent and the posterior margin of the sternum. The belly passes outward and forward, and inserts into the skin of the ventral abdominal feather tract, just posterior to the area of insertion of the anteriormost belly of the subcutaneous thoracis muscle.

M. supracoracoideus.--This muscle arises from approximately the dorsal half of the carina, from the medial part of the body of the sternum, from the coracold, and from the anterior surface of the coracoclavicular membrane in its lateral two-thirds.

The fleshy fibers insert on a median raphe and on a large tendon which, in typical manner, passes dorsad through the triosseal canal and then outward under cover of M. deltoideus minor to insert on the anterior edge of the humerus at the junction of the articu!ar head and the deltoid crest (Figure 4).

M. coracobrachialis anterior.--Appears to be absent in this species. M. coracobrachlalis posterior.--This muscle arises from the lateral surface of the

coracoid in slightly more than its basal half (Figure 4). The belly converges on a short tendon, which inserts on the internal tuberosity of the humerus.

M. sternocoracoideus.--The muscle arises primarily from the sternocoracoidal process of the sternum but has some fleshy fibers arising from the terminal ends of the

Oct., 1968] Myology of Kirtland's Warbler 599

sternal ribs (Figure 4). The belly passes forward and inward to insert on the sternocoracoidal impression on the posterior surface of the basal portion of the coracoid.

M. cucullaris pars propatagialis.--Pars propatagialis M. cucullaris is a long fleshy band (about 13 mm in length and 0.5 mm in width), which splits off the lateral surface of M. cucullaris at about the midlength of the neck (Figure 1). The belly gives rise to an elastic tendon at the level of the head of the humerus. The short tendon fuses

with the leading edge of the tendon of M. tensor patagii longus. Relative to some other species pars propatagialis is well developed in the Kirtland's Warbler.

M. tensor patagii longus.--Mm. tensores patagii longus et brevis are two entirely independent muscles in the warbler. M. tensor patagii longus is a small (3 mm long and 1.5 mm wide) fleshy muscle, which arises by an aponeurosis from the apex of the clavicle medial and adjacent to the semitendinous origin of M. tensor patagii brevis (Figure 1). The longus muscles passes outward superficial to the belly of the brevis muscle. The tendon of insertion of M. tensor patagii longus passes outward in the leading edge of the propatagium; the tendon has a strong attachment to the palmar surface of the os radiale and a smaller attachment to the posteropalmar corner of the base of the pollex; the tendon also is intimately related to the deep fascia in the region of the wrist and hand.

M. tensor patagil brevis.--M. tensor patagii brevis is a much larger muscle (about 9 mm in length and 3 mm in maximum width) than M. tensor patagii longus (Figure 1). The brevis muscle has a semitendinous origin from the apex of the clavicle, just medial to the coracoclavicular joint. The tendon of insertion passes distad in the propatagium and is anchored to the belly of M. extensor metacarpi radialis about 3.5 mm from its humeral origin, after which the brevis tendon passes proximad along the surface of M. extensor metacarpi radialis to insert on the ectepicondylar process of the humerus. Some fleshy fibers of M. extensor metacarpi radialis arise from the anterior edge of the tendon of M. tensor patagii brevis in its course proximad to the humerus. M. pectoralis propatagialis brevis is a small aponeurosis, which splits off the surface of M. pectoralis near its insertion; the aponeurosis fuses with the distal end of the belly of M. tensor patagii brevis and contributes to the formation of its tendon of insertion.

M. deltoideus major.--The major deltoid muscle has two well-developed heads (Figure 1).

a. The anterior head arises primarily by fleshy fibers from the large os humero- scapulare, but it also arises by a small tendon attached to the inferior edge of the acromion. The belly inserts by fleshy fibers on the deltoid crest for a distance of 10 mm and by a tendon on the ectepidondylar process of the humerus, anterior to the insertion of the posterior head.

b. The posterior head arises primarily by fleshy fibers from the medial surface of the apex of the clavicle; a small fascial band (scapular anchor) passes from the posterior margin of the proximal part of the belly to the scapula, a short distance cephalad to the anterior border of M. latissimus dorsi, pars anterior. There is, in addition, a small deep fasciculus (about 10 mm long), which arises from the posterior coracoclavicular ligament and which becomes aponeurotic and fuses with the deep surface of the posterior head. The posterior head inserts by fleshy fibers on a small area of the humerus just proximal and posterior to the ectepicondylar process. The anterior and posterior heads of M. deltoideus major are entirely independent in the Kirtland's Warbler; there is no fusion either at the origin or the insertion.

M. deltoideus minor.--M. deltoideus minor is a small band of fleshy fibers which

600 A•OaEW J. BERGER [Auk, Vol. 85

arises from the ventral edge of the tip of the acromion process of the scapula (Figure 2). The flat belly (about 1 mm in maximum width) passes outward, con- cealing the tendon of insertion of M. supraeoraeoideus, and inserts on the anterodorsal surface of the deltoid crest just distal to the insertion of M. supracoraeoideus.

M. biceps brachii.--M. biceps braehii arises by a strong, flat tendon from the anterolateral surface of the head of the eoraeoid and by a much thinner aponeurosis from the bicipital crest of the humerus, just distal to the artieular head and proximal to the origin of the ventral head of M. humerotrieeps (Figures 3, 4). The fleshy belly extends almost to the distal end of the arm, where a single tendon is formed. The tendon divides into two unequal parts: a very large tendon inserts on the proximal end of the ulna; a very small, fine tendon inserts on the proximal end of the radius. There is no biceps slip in Kirtland's Warbler.

M. triceps brachii.--M. seapulotrieeps arises by two well-developed heads. The posterior superficial head arises by fleshy fibers from the lateral surface of the aeromion and from the seapula posterior and inferior to the aeromion (Figure 1). The anterior deep head arises by tendinous fibers from the inferior edge of the scapula on the posterior surface of the glenoid lip and from the adjacent scapulohumeral ligament. The two heads fuse about half way down the arm; the common belly gives rise to a tendon near the distal end of the humerus. The tendon contains a sesamoid

where it crosses the distal end of the humerus; the tendon inserts on the posterior surface of the base of the eoronoid process of the ulna.

The external head of M. humerotrieeps is much larger at its origin than the internal head (Figures 1, 2, 4). The two heads arise within the well-developed double pneumatic fossa near the proximal end of the humerus. M. proseapulohumeralis inserts within the pneumatic fossa between the two heads of M. humerotriceps and just distal to the medial bar which lies between the two fossae. The two heads also arise

from the shaft of the humerus; they fuse to form a common belly. The tendon of insertion (which does not contain a sesamoid) inserts on the oleeranon process of the ulna, independent of the insertion of M. seapulotrieeps.

M. anconaeus coracoideus.--Both the long tendon of M. expansor seeundariorum and M. aneonaeus eoraeoideus are absent in the Kirtland's Warbler.

M. expansor secundarlorum.--M. expansor secundariorum is weakly developed in Kirtland's Warbler; the scapular tendon is absent. The muscle arises from the humeroulnar pulley only, which is an indirect rather than a direct origin from the humerus (Figure 3). The small, pale belly inserts on the bases of the inner two secondary feathers.

M. brachialis.--M. braehialis arises from the braehial impression on the humerus (Figure 3). The belly passes across the elbow palmar to the tendon of insertion of M. biceps braehii and inserts by fleshy fibers for a distance of about 2.5 mm (a relatively long area for the size of the bird) on the braehial impression on the ulna.

M. pronator superficialis.--The bellies of all the flexor muscles of the forearm are limited to slightly more than the proximal half of the forearm. M. pronator superficialis has the most proximal origin of those muscles arising from the distomedial surface of humerus (Figure 3). The belly (about 10 mm in length) passes distad and inserts on the anteroventral surface of the radius primarily by fleshy fibers but by an aponeurosis distally.

M. pronator profundus.--M. pronator profundus has an unusual origin by two distinct heads in the Kirtland's Warbler. There is a typical origin from the humerus by a short tendon which gives rise to a 9 ram-long fleshy belly (Figure 3). The belly tapers to a flat tendon which inserts on the radius posterior to the most distal

Oct., 1968] Myology o) • Kirtland's Warbler 601

area of insertion of M. pronator superficialis. A second (unusual) fleshy head arises from the humeroulnar pulley, deep to the belly of M. flexor carpi ulnaris. This well-developed belly fuses, in part, with the deep surface of the main belly but also gives rise to an aponeurosis that inserts on the radius, beginning a short distance beyond the insertion of the biceps brachii tendon and extending to the insertion of the tendon of the main belly. The aponeurosis is intimately retated to the deep surface of the main belly and its tendon of insertion.

M. )•lexor digitorum super)•icialis.--This muscle has a typical origin by a tendon from the medial humeral epicondyle (Figure 3). The tendon of origin fans out into a dense humerocarpal band, which envelops (i.e. conceals) the belly of M. flexor digitorum superficialis and most of the belly and tendon of insertion of M. flexor carpi ulnaris. Posteriorly, the humerocarpal band fuses with the fascia surrounding the bases of all but the most proximal secondaries and their under coverts (i.e. those receiving the expansor secundariorum muscle). Distally the humerocarpal band attaches to the palmar surface of the os ulnare and then continues around the wrist and into the hand, where it has three main attachments: (1) a strong slip to the base of the pollex, (2) to the carpometacarpus forming a vaginal sheath around the tendon of M. flexor digitorum profundus, (3) the bulk of the band fans out over the posterior aspect of the hand, attaching to metacarpal III and to the bases of the inner four primaries.

The belly of M. flexor digitorum superficialis is about 7 mm long; its fleshy fibers begin close to the humeral origin of its tendon. The long fine tendon of insertion passes distad on the deep surface of the humerocarpal band, through a groove on the anterior surface of the os ulnare, and into the hand. The tendon passes deep to the tendon of M. flexor digitorum profundus near the distal end of the carpometacarpus and inserts on the base of the proximal phalanx of digit II.

M. )•lexor dlgitorum profundus.--M. flexor digitorum profundus has a V-shaped origin by two fleshy heads, one arising on either side of the area of insertion of M. brachialis (Figure 3). The belly (about 9 mm in length) extends slightly beyond the midlength of the forearm. The tendon of insertion passes through a groove on the anterior surface of the os ulnare and then around the anterior surface of the pisi-

form process. The tendon crosses superficial to the tendon of M. flexor digitorum superficialis near the distal end of the carpometacarpus and inserts on the base of the distal (second) phalanx of digit II.

M. flexor carpi ulnaris.--M. flexor carpi ulnaris arises by a strong tendon from the distal end of the medial epicondyle of the humerus (Figure 3). The tendon passes through a strong humeroulnar pulley and then gives rise to a fleshy belly 10 mm in length. From its posterior and deep surface, the belly gives rise to two small fleshy fasciculi; these end in tendons, which send tendinous slips to the bases of the outer five secondary flight feathers. The rounded, well-developed, main tendon of insertion passes down the forearm and inserts on the proximal face of the os ulnare.

M. ulnlmetacarpalis ventralis.--This is a well-developed two-headed muscle (about 8.5 mm long), which has relatively a far proximal origin for this muscle: beginning posterior to the distal part of the insertion of M. brachialis (Figure 4). The proximal head of M. ulnimetacarpalis ventralis arises by fleshy fibers from the ventral surface of the ulna, posterior to the origin of M. flexor digitorum profundus. The latter muscle conceals all but the most distal part of the belly of M. ulnimetacarpalis ventralis. A short distal head arises from the anteroventral surface of the ulna about

its midlength. The two heads fuse on a common tendon. The strong, flat tendon of


insertion passes dorsad in a groove on the os radiale and inserts on the anterodorsal corner of the base of the carpometacarpus.

M. extensor metacarpi radialis.--M. extensor metacarpi radialis is composed of a single belly (about 11 mm long), which is limited to slightly less than the proximal two-thirds of the forearm (Figures 1, 3). The muscle arises by a tendon from the lateral epicondyle of the humerus. The belly gives rise to a single strong tendon, •vhich inserts on the extensor process of the carpometacarpus.

M. extensor metacarpi ulnaris.--This muscle arises by a thin tendon from the distal end of the humerus, posterior but adjacent to the origin of M. extensor digitorum communis, and proximal to the origin of M. anconeus (Figure 1). The tendon of origin sends a slip posteriorly to attach to the ulna, thus forming an ulnar anchor. The fleshy belly of M. extensor metacarpi ulnaris begins at the apex of the resulting V-shaped tendon, about 2 mm from the humeral origin of the tendon. The belly of the muscle (about 10 mm long) extends slightly more than halfway down the forearm. The tendon of insertion crosses the wrist joint and inserts on a tubercle on the posterior edge of metacarpal III about 3 mm from the base of the carpometacarpus.

M. extensor digitorum communis.--This muscle has a tendinous origin from the distal end of the humerus at the base of the distal surface of the ectepicondylar process (Figure 1). The belly (about 9 mm long) is limited to less than the proximal half of the forearm. The tendon of insertion has a typical course around the distal end of the ulna and into the hand. The tendon bifurcates at the level of the base of

the pollex. The short branch of the tendon inserts on the posterodorsal corner of the pollex. The long branch of the tendon makes a right-angle turn around a tubercle on the carpometacarpus and then passes distad in a groove on the anterodorsal edge of metacarpal II. At about the midlength of that bone, the tendon moves to its dorsal surface and passes deep to the tendon of M. extensor indicis longus. Near the distal end of the carpometacarpus, the tendon of M. extensor digitorum communis passes around the posterior surface of a bony flange and inserts on the base of the proximal phalanx of digit II.

M. anconeus.--M. anconeus has the most distal origin of the extensor muscles arising from the humerus (Figure 1). It arises distal to, and completely independent from, the tendon of origin of M. extensor metacarpi ulnaris. The belly of M. anconeus (about 8 mm long) inserts by fleshy fibers on the anterodorsal surface of the ulna; the belly is limited to approximately the proximal half of the forearm.

M. suplnator.--M. supinator is a very small muscle in the warbler; it arises by a fine tendon from the distal end of the humerus, deep to the tendon of origin of M. extensor digitorum communis (Figure 4). The fleshy belly (4 mm in total length) of M. supinator fans out from its tendon of origin and inserts on an area about 2 mm long on the proximal end of the radius.

M. extensor indicis longus.--The spindle-shaped fleshy belly (about 11 mm long) of M. extensor indicis longus arises from the posterior surface of approximately the proximal half of the radius, beginning at the level of insertion of M. biceps brachii on the radius (Figures 2, 4). The tendon of M. extensor indicis longus curves around the external ulnar condyle and into the hand. The tendon passes diagonally forward along the carpometacarpus, passing superficial to the tendon of M. extensor digitorum communis, and then along the anterodorsal surface of the proximal phalanx of digit II. The tendo.n inserts on the base of the distal (second) phalanx of digit II. A distal head ("M. flexor metacarpi brevis") of M. extensor indicis longus is absent.

M. extensor pollicis longus.--M. extensor pollicis longus has a very tiny belly (about

Oct., 1968] Myology o] Kirtland's Warbler 603

5 mm long and 0.2 mm wide), which arises by fleshy fibers from the anterodorsal surface of the coronoid process of the ulna (Figure 2). The belly tapers to a hairlike tendon, which inserts on the extensor process of the carpometacarpus, dorsal and adjacent to the tendon of insertion of M. extensor metacarpi radialis.

M. ulnimetacarpalis dorsalis.--This muscle is absent in the warbler. M. extensor pollicls brevis.--This muscle is absent in the warbler. M. abductor polllcls.--This muscle arises for a distance of about 1 mm from the

ventral edge of the tendon of insertion of M. extensor metacarpi radialis, just before it inserts on the extensor process of the carpometacarpus (Figure 3). The belly of M. abductor pollicis is about 3 mm long. It inserts by a flat tendon on a small tuberosity on the posterodorsal edge of the pollex about one-third the way distad from its base.

M. adductor polllcis.--This is a tiny (about 0.1 mm in diameter), but long (2 mm), muscle, which arises from the carpometacarpus opposite the base of the pollex (Fig- ure 3). The belly inserts by fleshy fibers near the tip of the posterior surface of the pollex.

M. flexor pollids.--This muscle is absent in the warbler. M. abductor indlcis.--This muscle is absent in the warbler.

M. interosseus dorsalls.--M. interosseus dorsalis has a very small (2 mm long) fleshy belly, which arises from the metacarpals at the proximal end of the intermetacarpal space (Figure 1). The belly tapers to a tiny tendon that inserts on the anterodorsal corner of the base of the distal phalanx of digit II.

M. interosseus palmaris. M. interosseus palmaris has a belly about 4 mm in length and is much wider than the belly of M. interosseus dorsalis (Figures 2, 3, 4). Both muscles arise from the proximal portion of the intermetacarpal space. The tendon of M. interosseus palmaris passes to the dorsal surface of the hand at the distal end of the carpometacarpus, passes distad along the posterodorsal surface of the proximal phalanx of digit II, and inserts on the posterodorsal corner of the base of the distal phalanx. Fascial extensions of the tendon continue distad and fuse with the fascia surrounding the digital primaries.

M. flexor diglti ///.--The fleshy belly of M. flexor digiti III arises from the posterior surface of metacarpal III in approximately its basal one-half (Figure 3). The belly ends on a small tendon, which passes distad along the metacarpal and inserts on the poorly developed posterior spine of digit III a short distance distal to its base.

MUSCLES OF TIlE LEG

M. sartorious.--This is a thin strap of muscle with a maximum width of 3 mm at its origin (Figure 5). It arises by an aponeurosis from the neural spine of the last (fifth) dorsal vertebra and by fleshy fibers from the anterior iliac process just anterior to the origin of M. iliotrochantericus anterior. The belly passes down the anterior surface of the thigh, passing medially as it approaches the knee, and inserts primarily by fleshy fibers on the anteromedial surface of the head of the tibiotarsus under cover of the most proximal fibers of M. gastrocnemius pars interna. Part of the belly of M. sartorious inserts on the medial surface of the patellar ligament a short distance before it inserts.

M. illotibialis.--The relationships of M. iliotibialis to the other muscles of the thigh are similar to those in most other passerine birds thus far studied: M. iliotibialis conceals most of the muscles on the lateral surface of the thigh, including all but the tendon and most distal part of the belly of M. biceps femoris (Figure 5). M. iliotibialis arises by an aponeurosis from the anterior iliac crest and most of the posterior iliac crest; the most posterior part of the muscle arises by fleshy fibers. Anteriorly, the aponeurosis of origin conceals Mm. iliotrochantericus posterior and iliotrochanteri-

604 ANDREW J. BERGER

Aponeurotic Oil

[Auk, Vol. 85

Gastrocn ernius pars

Flexor perf, et perf, digiti

Peroneus

Tibialis

Peroneus

Semitendinosus

semitendinosus

perL et perf, digiti

pars externa

hallucis longus

caudae

eaudoe

'Depressor coudae

pars caudofemoralis

Ligamenturn cartilage

Extensor dlgitorurn

IC) mm

Figure 5. muscles.

I

Lateral view of the left leg of Kirtland's Warbler to show the superficial

cus anterior. The central part of M. iliotibialis is aponeurotic in its distal three-fourths. The fleshy anterior and posterior parts of the belly become aponeurotic a short distance proximal to the knee. The common aponeurosis of the three parts of the muscle forms the anterior layer of the patellar ligament.

M. iliotrochanterlcus posterior.--This relatively large muscle arises by fleshy fibers from the bone of the entire anterior iliac fossa and from the anterior iliac crest

Oct., 1968] 605 Myology o! Kirtland's Warbler

[liotrochantericus medius

Iliotrochantericus

Iliatrochantericus

Femorotibialis

Femorotibialis distal

Flexor per• et per• digit[

Flexor per• etper• digiti

Tibialis

Biceps femoris

loop

Flexor perforatus digit[ ]•

perforatus digitl

perforatus digit[ •T

hallucis longus

Peroneus

I0 turn

Flexor perforatus digit[

Flexor digitorum Iongu

Flexor perf. et perf. digiti iT

Flexor perf, et perf. dig[ti m

perforatus digill gZ

Flexor perforatus digiti lTr

Figure 6. Lateral view of the left leg of Kirtland's Warbler to show a deep layer of muscles and the pattern of insertion of the flexor tendons o.n digits II, III, and IV. The following muscles have been removed: sartorius, iliotibialis, piriformis pars caudofemoralis, gastrocnemius, and peroneus longus.

606 ANDREW J. BERGER [Auk, Vol. 85

to about the level of the anterior margin of the acetabulum (Figure 6). The well- developed belly ends on a wide (about 1.5 mm), flat tendon, which inserts on a curved ridge on the lateral surface of the femur just distal to the trochanter. The belly of M. iliotrochantericus posterior conceals Mm. iliotrochantericus medius and iliacus.

M. •liotrochantericus anterior.--This muscle arises primarily by fleshy fibers from the tip of the anterior iliac process of the ilium, adjacent to the origin of M. sartorius, and from the ventrolateral edge of the ilium for a distance of about 1.5 mm (Figure 6). The well-developed belly passes backward and outward to insert between the bellies of Mm. femorotibialis externus and femorotibialis medius on the posterolateral surface of the shaft of the femur, beginning about 2.5 mm from the proximal end of the bone.

M. illotrochanterlcus medius.--This is a small muscle about 4 mm long and little more than 0.5 mm in maximum width at its origin from the ventrolateral edge of the ilium posterior to the origin of M. iliotrochantericus anterior (Figure 6). The nerve to M. iliotrochantericus posterior passes dorsad between the bellies of Mm. iliotrochantericus anterior and iliotrochantericus medius. The belly of M. iliotrochantericus medius passes backward and outward dorsal to the belly of M. iliotrochantericus anterior, tapers to a narrow thin aponeurosis, and inserts on the posterolateral surface of the femur a short distance proximal to the insertion of M. iliotrochantericus a.n- terior and immediately anterior to the most proximal fibers of origin of M. femorotibialis externus.

M. gluteus medius et minlmus.•This muscle, "D" in leg-muscle formulae, is absent in Kirtland's Warbler.

M. femorotibialis externus.--This muscle arises from the lateral and posterolateral surfaces of the femur, beginning about 1.5 mm from the proximal end of the bone and extending distad for most of the length of the femoral shaft (Figure 6). The fleshy fibers begin at the level of insertion of M. ischiofemoralis, which is a short distance proximal to the areas of insertion of Mm. iliotrochantericus anterior et medius.

The anteromedial border of M. femorotibialis externus is inextricably fused with M. femorotibialis medius. As it approaches the knee, the belly of M. femorotibialis externus gives rise to an aponeurosis, which forms the lateral portion of the patellar ligament.

A relatively long distal head lies deep to the proximal head and arises from the posterolateral surface of the distal half of the femur. The distal head also ends on an aponeurosis; it forms the deep layer of the most lateral part of the patellar ligament.

M. femorotibialis medius.--The largest of the three parts of this complex (Figures 6, 7), M. femorotibialis medius arises primarily by fleshy fibers from the trochanteric ridge and the anterior surface of the shaft of the femur throughout nearly its entire length. Mm. femorotibialis externus et medius are intimately fused throughout their length except proximally, where the two muscles are separated by the tendon of insertion of M. iliotrochantericus anterior.

The fleshy fibers of M. femorotibialis medlus insert on the proximal surface of the patella. The lateral portion of the muscle also gives rise to aponeurotic fibers, which aid in the formation of the patellar ligament.

M. femorotibialis internus.--M. femorotibialis internus has two independent bellies in the Kirtland's Warbler. The proximal or "typical" belly is a long (about 11 mm), spindle-shaped muscle arising from the medial surface of the femur, beginning just distal to the insertion of M. iliacus about 3 mm from the proximal end of the femur


(Figure 7). The proximal belly ends on a narrow flat tendon, which inserts on the anteromedial corner of the head of the tibiotarsus.

The deep distal belly (about 5 mm long) arises from the medial surface of the femur just proximal to the internal femoral condyle. The belly ends on a flat tendon; it inserts on the tibiotarsus posterior and adjacent to the insertion of the tendon of the proximal belly.

M. biceps femoris.--This muscle arises by an aponeurosis from the most caudal portion of the anterior iliac crest (dorsal to the acetabulum) and from approximately the anterior 3 mm of the posterior iliac crest (Figures 5, 6). In some specimens a small portion of the dorsal border of M. ischiofemoralis may be visible between the posterior border of the biceps muscle and the anterior border of M. semitendinosus. The belly of the biceps muscle passes downward, tapers to a small tendon, descends through the biceps loop, and inserts on the posterior face of the shaft of the fibula about 3 mm from the proximal end of the bone.

The biceps loop has three arms: two femoral and one fibular (Figure 6). The proximal femoral arm (about 0.5 mm wide) is attached to a ridge on the anterolateral surface of the femur 3 mm from the distal end of the bone. The narrower distal

arm is attached to the posterolateral surface of the femur just proximal to the external femoral condyle. The distal femoral arm and the aponeurosis of M. gastrocnemius pars externa are inextricably fused. The fibular arm passes forward deep to the common aponeurosis of origin of Mm. flexor perforans et perforatus digiti II and flexor perforans et perforatus digiti III and attaches to the anterior edge of the fibula about 1.5 mm from the proximal articular surface.

M. semitendlnosus.--M. semitendinosus arises by fleshy fibers from the posterior 1.5 mm of the posterior iliac crest and by an aponeurosis from ligaments and fascia extending between the first free caudal vertebra and the caudal end of the ilium (Figures 5, 6). The small belly (about 2.5 mm wide) of the semitendinosus muscle passes downward and forward, superficial to M. piriformis pars caudofemoralis, and ends on a ligamentous raphe shared by the t•vo parts of the semitendinosus complex.

The accessory semitendinosus muscle is a small band (about 4 mm long and 2 mm wide) of fleshy fibers extending between the distal end of the femur and the common raphe. The accessory semitendinosus muscle inserts on the posterior surface of the femur just proximal to the external condyle, beginning between the two fernoral arms of the biceps loop and extending medially in the popliteal fossa of the femur to the inner surface of the internal femoral condyle and the origin of M. gastrocnemius pars media.

The inconspicuous and relatively delicate raphe which separates the semitendinosus and the accessory semitendinosus muscles fans out into a narrow aponeurosis inferior to the bellies of the muscle. Part of the aponeurosis fuses with the superior border of the tendon of insertion of M. semimembranosus and inserts with it on the tibio-

tarsus. The remainder of the aponeurosis inserts on the distal end of the belly of M. gastrocnemius pars media.

M. piriformis.--a. Pars i]iofemoralis is absent in the Kirtland's Warbler. b. Pars caudofemora]is arises by a small tendon (about 2 mm long) from the

posterolateral corner of the base of the pygostyle (Figure 5). From its minute tendon of origin, the belly expands within a short distance to a maximum width of about 3 mm. The belly passes forward, deep to M. semitendinosus and superficial to M. ischiofemoralis, and inserts by tendinous fibers (1 mm wide) on the posterior surface of the femur, beginning about 4.5 mm from the proximal end of the bone.

M. ischiofemoralis.--This muscle arises by fleshy fibers from most of the lateral

608 ANDSEW J. BrRCrR [Auk, Vol. 85

Jliot rochont ericus [liotrochanterlcus medius

Femorotibialis

Femorotibialls

Gastrocnemius pars

internus

Adductor longus et brevis anterior

longus et brevis posterior

pars media

pars externa

Peroneus

TibiaIls

I0 mm

Ligamenium

ibiaI cart,lage

•ypotarsus

Achillis

/

Figure 7. A medial view of the pelvis and right leg of Kirtland's Warbler. Only the skin and superficial fascia have been removed.


surface of the ischium and from the ventral surface of the small projecting posterior iliac crest (Figure 6). A small area on the posteroventral surface of the ischium between 3/1. ischiofemoralis (anteriorly and superiorly) and 3/1. semimembranosus (posteriorly and inferiorly) is devoid of any muscle attachment.

The tendon of insertion of M. ischiofemoralis forms on the superficial surface of the belly, tapers to a width of about 0.75 mm and inserts on a ridge on the lateral surface of the femur beginning about 1.5 mm from the proximal end of the bone.

M. semimembranosus.--3/l. semimembranosus arises by fleshy fibers from an area approximately 2.5 mm wide on the posteroventral surface of the ischium just dorsal to the ischiopubic fenestra (Figure 7). The small flat band of fleshy fibers (about 2 mm in maximum width) enters the leg musculature by passing between pars interna and pars media of 3/1. gastrocnemius, gives rise to a flat aponeurosis about 1.5 mm wide, and inserts on the posteromedial surface of the tibiotarsus, beginning about 2 mm from the proximal articular surface of the bone.

M. adductor longus et brevis.--This muscle consists of two independent bellies which, i.n passerine birds, are named pars anterior and pars posterior, although pars posterior also lies on a deeper plane (Figure 7).

a. Pars anterior arises by means of fleshy fibers from the ventrolateral surface of the ischium along a line 3 mm long, beginning at the level of the caudal border of the obturator foramen. The flat bandlike belly passes downward and forward to insert by fleshy fibers on the posterior surface of the femur in approximately its distal two-thirds.

b. Pars posterior arises by a thin aponeurosis (1.5 mm wide) from the ventrolateral surface of the ischium ventral to, and between, the areas of origin of M. adductor longus et brevis pars anterior and M. semimembranosus. The thin, small (slightly more than 1 mm wide), fleshy belly of pars posterior passes downward and forward, deep and posterior to pars anterior, to insert in common with the origin of 3/1. gastrocnemius pars media on a prominent tubercle on the posteroproximal end of the internal femoral co.ndyle.

M. obturator externus.--3/l. obturator externus is composed of two independent bellies.

a. The dorsal belly arises by fleshy fibers from the ischium at the posterodorsal border of the obturator foramen. The small (2 mm long), fleshy belly passes outward and forward to insert on the superficial surface of the tendon of insertion of M. obturator internus.

b. The ventral belly arises from the ischium at the anteroventral border of the

obturator foramen. The rectangular-shaped belly passes outward and inserts by fleshy fibers on the posterior surface of the femur immediately distal to the insertion of 3/1. obturator internus.

M. obturator internus.--This is a triangular-shaped muscle arising by fleshy fibers from the medial surface of the pubis, ischiopubic membrane, and the ischium (Figure 7). Fleshy fibers converge on a well-developed tendon. It passes outward through the obturator foramen and inserts on the posteroproximal end of the femur just distal to the trochanter.

M. iliacus.--This is a tiny band of fleshy fibers about 3 mm long and 0.2 mm in maximum width (Figure 7). The muscle arises from the ventral edge of the ilium immediately posterior to the origin of M. iliotrochantericus medius. 3/1. iliacus passes backward and outward to insert on the medial surface of the femur about 2 mm from

the proximal end of the bone and just proximal to the origin of 3/1. femorotibialis internus.


M. ambiens.--The ambiens muscle is absent in Kirtland's Warbler.

M. gastrocnemius.--The gastrocnemius muscle has three typical heads in the warbler. a. Pars externa has a well-developed belly (14 mm long) extending about half way

down the crus (Figures 5, 7). Pars externa arises by an aponeurosis from a tubercle on the posterolateral surface of the femur just proximal to the lateral condyle. The aponeurosis of origin is fused to the superficial surface of the distal arm of the biceps loop. The belly of pars externa passes distad superficial to the tendon of insertion of M. biceps femoris and ends on a strong tendon, which forms the most lateral part of the common tendo achillis of the gastrocnemius complex.

b. Pars media is a small muscle (about 6 mm long) arising from a prominent tubercle on the posteroproximal surface of the internal fernoral condyle. The origin on the tubercle is shared with the insertion of M. adductor longus et brevis pars posterior. The belly of pars media ends on an aponeurosis, which passes downward between the bellies and tendons of pars externa and pars interna to form the central part of the tendo achillis.

c. Pars interna is the most superficial muscle on the anterior and medial surfaces of the proximal end of the crus. The muscle arises by fleshy fibers from the medial surface of the inner cnemial crest and the head of the tibiotarsus. A small band of

fleshy fibers (about 6 mm long) arises from the anterior surface of the patellar ligament, passes distad across the medial surface of the knee joint (superficial to the insertion of M. sartorius), and ends on the superficial surface of the main head. The fleshy belly of pars interna ends on a tendon a short distance proximal to the termination of the belly of pars externa; the tendon forms the medial portion of the tendo achillis.

The common tendon of insertion of the three parts of M. gastrocnemius passes distad over the posterior surface of the tibial cartilage, inserts on the posterior surface of the hypotarsus, and continues distad to insert on the posterolateral ridge of the tarsometatarsus and to fuse with the deep fascia on the posterior surface of that bone, thus aiding in forming a vaginal sheath for all of the flexor tendons passing to the toes.

M. tibiaIis anterior.--All but the most distal end of the tibial head and the common

belly of M. tibialis anterior lie deep to the relatively large expanded belly of M. peroneus longus (Figures 5, 6, 7).

a. The tibial head of M. tibialis anterior arises, under cover of M. peroneus longus, from a small area on the lateral surface of the inner cnemial crest and from a relatively large area on the medial surface of the outer cnemial crest of the tibiotarsus.

b. The long (15 mm), spindle-shaped femoral head arises by a short (about 0.5 mm long), but stout, tendon from a pit on the apex of the external fernoral condyle. The fleshy belly passes downward in the interval between the heads of the fibula and the tibiotarsus and then down the anterior surface of the tibiotarsus deep to the tibial head of the muscle. The two heads remain independent a little over one-third

the way down the crus. The fernoral head fuses with the deep surface of the tibial head just proximal to the formation of the tendon of insertion. The overall length of the tibial head and the common belly is about 15 mm; the muscle extends slightly more than half way down the crus.

c. The single large tendon of insertion passes distad deep to the ligamenturn transversum, but superficial to the tendon of M. extensor digitorum longus, and inserts on the anterior surface of the tarsometatarsus 1.5 mm from the proximal end of the bone.

M. extensor digitorum longus.--The small belly of M. extensor digitorum longus is limited to approximately the proximal third of the crus, although the muscle has a relatively large origin from most of the lateral surface of the inner cnemial crest,


from the base of the outer cnemial crest, and from the anterior surface of the head and proximal end of the shaft of the tibiotarsus (Figure 5). The belly passes downward medial to the femoral head of M. tibialis anterior and rapidly tapers to a small tendon.

The tendon passes under the ligamentum transversum, deep to the tendon of M. tibialis anterior, and then through a bony canal just above the condyles of the tibiotarsus. The tendon passes through a second bony canal on the proximal end of the tarsometatarsus and then continues distad medial to the tendon of insertion of M.

tibialis anterior and lateral to the belly of M. extensor hallucis longus. The tendon trifurcates near the distal end of the tarsometatarsus.

Small tendons pass along the dorsal surfaces of digits II and IV. The primary insertion of each tendon is on the dorsal surface of the base of the terminal (ungual) phalanx of those digits, but small branches of each main tendon also insert on the bases of all but the proximal phalanx of each digit.

The branch of the main tendon to digit III is larger than the other two tendons combined. The tendon passes along the dorsal surface of the proximal phalanx of digit III and bifurcates at about the midlength of the phalanx. The resulting medial and lateral branch tendons insert on the dorsal surface of the base of the terminal

phalanx and also send branches to insert on the base of the third phalanx of the digit.

M. peroneus longus.--M. peroneus longus conceals all but the most distal part of the belly of M. tibialis anterior (Figures 5, 7). The fleshy belly (12 mm long) of M. peroneus longus is located in slightly less than the proximal half of the crus. The belly arises primarily by fleshy fibers along a narrow line on the anterior edge of the inner cnemial crest, the rotular crest, and the outer cnemial crest of the tibiotarsus. The belly tapers to a small tendon which bifurcates a short distance (1.5 mm) from the proximal end of the tibial cartilage. One branch continues in the direction of the common tendon and inserts on the proximolateral corner of the tibial cartilage. A slightly narrower (but longer) branch passes downward and forward over the lateral condyle, passes superficial to the tendon of insertion of M. peroneus brevis, and inserts on the tendon of M. flexor perforatus digiti III about 2.5 mm inferior to the proximal end of the tarsometatarsus.

M. peroneus brevis.--M. peroneus brevis has a small spindle-shaped belly (about 12 mm long) arising from the anterior surface of the shaft of the fibula, beginning just proximal to the insertion of M. biceps femoris (Figures 5, 6). The tendon of insertion of M. peroneus brevis is held in place by a ligament on the anterolateral surface of the tibiotarsus at the level of the ligamentum transversum. The tendon passes deep to the long tendon of M. peroneus longus and inserts on a tubercle on the lateral surface of the proximal end of the tarsometatarsus.

M. flexor perforans et perforatus digitl Ill.--This is the most superficial muscle on the lateral surface of the crus, lying anterior to Mm. gastrocnemius pars externa and flexor perforans et perforatus digiti II and posterior to M. peroneus longus (Figures 5, 6).

The 15 ram-long belly of M. flexor perforans et perforatus digiti III arises by two short heads. Because of their fascial covering, the two heads are not distinct on the superficial surface of the muscle. The anterior head arises primarily by fleshy fibers from the lateral surface of the outer cnemial crest and from the head of the fibula.

The posterior head arises by an aponeurosis from the lateral fernoral condyle, just distal to the origin of M. flexor perforans et perforatus digiti II, and from the patellar ligament. The two heads fuse after independent courses of about 3 mm•

The common belly tapers to a small tendon, which passes down the posterior surface

612 ANDREW J. BEROER [Auk, Vol. 85

of the crus under cover of the gastrocnemius muscle and tendon, through a fibrous canal in the roedial half of the tibial cartilage, and then through the most superficial bony canal on the medial side of the hypotarsus in company with the tendon of M. flexor perforans et perforatus digiti II. There is no vinculum between the tendons of Mm. flexor perforans et perforatus digiti III and flexor perforatus digiti III.

The tendon of M. flexor perforans et perforatus digiti III expands at the distal end of the tarsometatarsus, ensheathes the tendon of M. flexor digitorum longus, and then perforates the tendon of M. flexor perforatus digiti III. The tendon splits, allowing the passage of the tendon of M. flexor digitorum longus, near the distal end of the second phalanx of digit III. The two branches insert, respectively, on the medial and lateral corners of the base of the third phalanx of digit III.

M. flexor perjorans et perforatus digiti//.---This is a tiny muscle with a belly 5 mm in length. The proximal half of the belly is visible anterior to the origin of M. gastrocnemius pars externa but the distal half of the belly is concealed by pars externa (Figures 5, 6). M. flexor perforans et perforatus digiti II arises from a small area on the posteroproximal face of the lateral femoral condyle just distal to the origi.n of M. gastrocnemius pars externa.

The mi.nute tendon of M. flexor perforans et perforatus digiti II passes distad deep to the belly and tendon of M. gastrocnemius, through a fibrous canal in the posterior surface of the tibial cartilage, and then traverses the most posterior (superficial) of the bony canals in the hypotarsus. The tendon continues down the posterior surface of the tarsometatarsus and through a large fibrocartilaginous pad at the base of digit II to reach the plantar surface of that digit. The tendon bifurcates at about the midlength of the phalanx. The tendon of M. flexor digitorum longus passes between the two resulting branches of the tendon. The roedial branch inserts on the medial corner of the base of the second phalanx of digit II. The lateral branch inserts on the plantar surface of the capsule of the interphalangeal joint between the proximal and second phalanges of the digit.

M. flexor perforatus digiti 1V.--Mm. flexores perforati digiti III et IV share a common fleshy origin from the intercondyloid region of the femur (Figure 6). This origin also is shared with the most medial of the three heads of M. flexor hallucis longus.

The 12 mm-long belly of M. flexor perforatus digiti IV descends along the back of the crus superficial to the belly and tendon of insertion of M. flexor perforatus digiti III and the most medial head of M. flexor hallucis longus, but medial to the main bulk of the belly of the latter muscle.

The tendon of M. flexor perforatus digiti IV passes over the back of the tibial cartilage and through the most superficial of the bony canals on the lateral surface of the hypotarsus; during the course the tendon of M. flexor perforatus digiti IV descends on the superficial or posterior surface of the tendon of M. flexor perforatus digiti III.

The tendon of M. flexor perforatus digiti IV expands at the distal end of the tarsometatarsus, ensheathes the tendon of M. flexor digitorum longus, and then splits to insert on the fibrocartilaginous pad and related capsular tissue on the plantar surface of the base of the third phalanx of digit IV.

M. flexor perforatus digiti Ill.--This muscle arises from the deep surface of M. flexor perforatus digiti IV, although fundamentally the two muscles share a common origin from the intercondyloid region of the femur.

The relatively long (about 14 mm) belly and tendon of insertion of M. flexor perforatus digiti III pass distad deep (medial) to the belly and tendon of M. flexor perforatus digiti IV (Figure 6). The tendon of M. flexor perforatus digiti III lies anterior to the tendon of M. flexor perforatus digiti IV as they cross the posterior


surface of the tibial cartilage and traverse the superficial bony canal in the lateral half of the hypotarsus.

The long tendon of M. peroneus longus inserts on the tendon of M. flexor perforatus digiti III just after that tendon emerges from the inferior surface of the hypotarsus. There is no vinculum between the tendons of M. flexor perforatus digiti III and M. flexor perforans et perforatus digiti III.

The tendon of M. flexor perforatus digiti III splits and thus allows the passage of the tendons of Mm. flexor perforans et perforatus digiti III and flexor digitorum longus at about the midlength of the proximal phalanx of digit III. The resulting two terminal branches of the tendon of M. flexor perforatus digiti III insert on the base of the second phalanx of digit III.

M. flexor perforatus digiti //.--This muscle arises by an aponeurosis (shared with M. flexor perforans et perforatus digiti II and the lateral head of M. flexor hallucis longus) from a small area on the posteroproximal face of the lateral fernoral condyle distal to the origin of M. gastrocnemius pars externa (Figure 6).

The small spindle-shaped belly (8 mm long) of M. flexor perforatus digiti II tapers to a very fine tendon. The tendon passes through a fibrous canal in the lateral half of the tibial cartilage deep to the tendons of Mm. flexor perforatus digiti III and flexor perforatus digiti IV, takes a diagonal course distad across the intertarsal joint, and traverses a deep bony canal on the medial surface of the hypotarsus.

The tendon of M. flexor perforatus digiti II is not perforated by either the tendon of M. flexor perforans et perforatus digiti II or by the tendon of M. flexor digitorum longus. The tendon passes through a canal in a large fibrocartilaginous pad at the base of the proximal phalanx of' digit II and then inserts on the proximomedial corner of the proximal phalanx of that digit.

M. plantaris.--This is a tiny triangular-shaped muscle with a belly about 3.5 mm in total length. The muscle arises by fleshy fibers from the posteromedial surface of the head of the tibiotarsus. The belly tapers to a fine tendon, which passes down the medial surface of the crus and inserts on the proximomedial corner of the tibial cartilage.

M. flexor hallucis longus.--M. flexor hallucis longus is peculiar in the warbler in that the muscle has three separate heads.

a. The most medial head arises in common with M. flexor perforatus digiti IV from the intercondyloid region of the femur.

b. The intermediate head arises by an aponeurosis from the posterolateral surface of the femur proximal to the external condyle and distal to the origin of M. gastrocnemius pars externa and medial to the origin of Mm. flexor perforans et perforatus digiti II and flexor perforatus digiti II (Figures 5, 6).

c. The lateral head arises by a small flat tendon attached to the distal end of the femur adjacent to the attachment of the origin of the intermediate head of the muscle and deep to the aponeurosis of origin of Mm. flexor perforans et perforatus digiti II and flexor perforatus digiti II. The tendon of the lateral head passes distad lateral to the fibular arm of the biceps loop and is fused with it. Fleshy fibers arise from the tendon at the level of insertion of the biceps tendon (i.e. about 5 mm distal to the fernoral origin of the tendon). The tiny 5 mm-long spindle-shaped belly of the lateral head ends on a tendon, which fuses with the proximal end of the main tendon derived from the common belly formed by the medial and intermediate heads of the muscle.

Both the medial and the intermediate heads of M. flexor hallucis longus pass distad medial to the biceps loop and the tendon of insertion of M. biceps femoris. The medial

614 ANDREW J. BERGER [Auk, Vol. 85

head fuses with the intermediate head about 8 mm inferior to their fernoral origins. The overall length of the intermediate head and the common belly is about 15 ram, extending a little more than half way down the crus.

The single tendon of insertion of M. flexor hallucis longus descends through a fibrous canal in the lateral half of the tibial cartilage and through the deepest (most anterior) bony canal in the lateral half of the hypotarsus. As it descends through the posterior compartment of the tarsus, the tendon of M. flexor hallucis longus crosses superficial to the tendon of M. flexor digitorum longus. The two tendons are not interconnected by a vinculum.

The tendon of M. flexor hallucis longus curves around the lateral surface of metatarsal I, passes through a well-developed fibrous pulley (perhaps a vestige of the tendon of insertion of M. flexor hallucis brevis), and reaches the plantar surface of the hallux. The main insertion is on the base of the terminal phalanx of the hallux, but a vinculum, derived from the deep surface of the tendon, inserts on the fibrocartilaginous pad between the proximal and distal phalanges of the hallux.

M. flexor digitorura longus.--This muscle arises by two typical heads: one from the posterior surface of the fibula; the other from the posterior surface of the tibiotarsus (Figure 6). The well-developed belly (about 15 mm in length) extends a little more than half way down the crus and ends on a large tendon. This tendon of insertion passes through the roedial half of the tibial cartilage and then through the deepest (most anterior) bony canal in the roedial half of the hypotarsus. Inferior to the hypotarsus, the tendon of M. flexor digitorum longus passes deep to the tendon of M. flexor hallucis longus and then lateral to it. There is no vinculum.

The tendon of M. flexor digitorum longus trifurcates at the level of metatarsal I. The small tendon to digit II passes through fibrous tissue at the base of the proximal phalanx of digit II and then along the plantar surface of the digit to insert on the base of the distal phalanx. A small vinculum arises from the deep surface of the tendon opposite the middle of the second phalanx of digit II; it inserts on the pad between the second and terminal phalanges of the digit. The main tendon does not perforate the tendon of M. flexor perforans et perforatus digiti II.

The tendon to digit III is much larger than the branches to digits II and IV. The branch to digit III passes between the two limbs of the tendon of insertion of M. flexor perforatus digiti III opposite the proximal phalanx, between the two limbs of the tendon of insertion of M. flexor perforans et perforatus digiti III near the distal end of the second phalanx, and then inserts on the plantar surface of the base of the distal phalanx. Small vinculae insert on the fibrous pads at the interphalangeal joints between the second and third and the third and fourth phalanges.

The small branch-tendon to digit IV is completely ensheathed by the tendon of M. flexor perforatus digiti IV at the base of the digit. It perforates that tendon at about the midlength of the proximal phalanx, and inserts on the plantar surface of the base of the distal phalanx. Vinculae from the deep surface of the tendon insert on the fibrous joint pads at the interphalangeal joints between the third and fourth and the fourth and fifth (terminal) phalanges.

M. popllteus.--M. popliteus is absent in the Kirtland's Warbler. M. flexor hallucls brevls.--This muscle is absent in the warbler. M. extensor hallucis longus.--This muscle is vestigial in Kirtland's Warbler. Its tiny

belly is about 6 mm in length and about 0.1 mm in maximum width. That this was indeed a muscle had to be confirmed by histological examination.

The muscle arises from the anteromedial surface of the tarsometatarsus, beginning about 1 mm from its proximal articular surface. The belly passes downward roedial to


the tendons of Mm. extensor digitorum longus and tibialis anterior and gives rise to a minute shiny tendon. The tendon moves gradually to the posteromedial surface of the tarsometatarsus, crosses the center of the trochlea of metatarsal I, and passes on to the dorsal surface of the proximal phalanx of the hallux. The tendon could not be traced to the distal phalanx; apparently, the tendon ends in the deep fascia on the dorsum of the hallux.

Ligaments o! the hallux.--A well-developed automatic extensor ligament of the hallux (George and Berger, 1966: 456) extends from the plantar-medial corner of the base of the proximal phalanx of the hallux to the dorsomedial corner of the base of the terminal phalanx of the hallux. The proximal attachment of the ligament is to a large fibrocartilaginous disc which interconnects the distal end of the troch!ea of metatarsal I and the base of the proximal phalanx of the hallux.

A strong automatic extensor ligament of the claw of the hallux extends from the dorsal surface of the distal end of the proximal phalanx to the base of the terminal phalanx of the hallux.

Short toe muscles absent.--As the following muscles could not be identified (with 20X magnification), they are considered to be absent in Kirtland's Warbler: Mm. abductor digiti II, adductor digiti II, extensor proprius digiti III, extensor brevis digiti III, extensor brevis digiti IV, abductor digiti IV, adductor digiti IV, and lumbricalis.

SUMMARY

The following wing muscles are absent in Kirtland's Warbler: latissimus dorsi pars posterior and pars metapatagialis, coracobrachialis anterior, the biceps slip, anconaeus coracoideus, entepicondyloulnaris, the distal head of M. extensor indicis longus, ulnimetacarpalis dorsalis, extensor pollicis brevis, flexor pollicis, and abductor indicis.

M. latissimus dorsi pars anterior inserts on the humerus anterior to the area of origin of the external head of M. humerotriceps, thus differing from the pattern of insertion in most passerine species.

M. pronator profundus has a double origin in Kirtland's Warbler: a typical tendinous origin from the distal end of the humerus, and an unusual fleshy origin from the humeroulnar pulley.

M. ulnimetacarpalis ventralis is unusual in that it has. both' a proximal and a distal head of origin.

As is true for all passerine birds thus far studied, the leg-muscle formula of Kirtland's Warbler is ACEFXY (George and Berger, 1966: 236). The following formulae muscles, therefore, are absent in all passerine birds studied: piriformis pars iliofemoralis (B), gluteus medius et minimus (D), popliteus (G), ambiens (Am), and the vinculum (V) between the tendons of insertion of Mm. flexor perforatus digiti III and flexor perforans et perforatus digiti III. In addition, the following short toe muscles are absent in Kirtland's Warbler: Mm. abductor digiti II, adductor digiti II, extensor proprius digiti III, extensor brevis digiti III, extensor brevis digiti IV, abductor digiti IV, adductor digiti IV, and lumbricalis. M. flexor hallucis longus is unusual in that it arises by three distinct heads.

616 A•I)REW J. BERCE• [Auk, Vol. 85

LITERATIJRE CITED

BEacon, A. J. 1956. The expansor secundariorum muscle, with special reference to passerine birds. J. h/iorphol., 99: 137-168.

B•o•R, A. J. 1957. On the anatomy and relationships of Fregilupus varius, an extinct starling from the Mascarene Islands. Bull. Amer. Mus. Nat. Hist., 113: 225-272.

B•g•, A. J. 1966. Experiences with insectivorous birds in captivity. Jack-Pine Warbler, 44: 65-72.

GEo•g•, J. C., Axm A. J. B•g•R. 1966. Avian myology. New York, Academic Press. Gool)wI•, H. A., et al. 1966. Rare and endangered fish and wildlife of the United

States. Resource Publ. 34, Washington, D.C., Bureau of Sport Fisheries and Wildlife.

MAYVi•LI), H.F. 1962. 1961 decennial census of the Kirtland's Warbler. Auk, 79: 173-182.

Department of Zoology, University of Hawaii, Honolulu, Hawaii 96822.

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