The Appendicular Myology of the Labrador Duck (Camptorhynchus Labradorius)

Condor, 80:407-418 0 The Cooper Ornithological Society 1978

THE APPENDICULAR MYOLOGY OF THE LABRADOR DUCK (CAMPTORHYNCHUS LABRADORIUS)

RICHARD L. ZUSI AND GREGORY DEAN BENTZ

The Labrador Duck (Camptorhynchus labra- on either humeral element. The remainder of dorius, Gmelin) has been extinct for almost the forelimb bones and muscles were in sur- 100 years, the last specimen having been prisingly good condition. As all the feathers taken in 1878. The species occurred formerly were retained with the skin, M. expansor along the east coast of North America from secundariorum could not be demonstrated. the Ungava Peninsula to the Delaware River Each hindlimb included the distal half of the and perhaps to Chesapeake Bay (Palmer tibiotarsus, the tarsometatarsus, and all pha- 1976). Little is known about its habits or in- langes of all toes except the ungual pha- ternal anatomy, and nothing is known about langes, which remained with the skin. In some its myology. instances complete bellies of muscles were The purpose of this paper is to describe absent and only the tendon of insertion is de- the distal musculature of the wing and leg of scribed. Also, due to the extremely dehy- the Labrador Duck. The unique history of drated condition of all muscles, the presence a study skin of an adult male in the collections of several small muscles and fiber architecture of the Smithsonian Institution (USNM 1972) even of larger ones could not always be dem- gave us the opportunity to do this. About onstrated. Dissection was performed with a twenty years ago, Humphrey and Butsch stereomicroscope and drawings were made (1958) realized that they could study the with the aid of a camera lucida microscope pterylosis and osteology of the Labrador Duck attachment. We referred to one fluid speci- by temporarily dismantling a study skin of men each of Oldsquaw (Clangula hyemalis) the species. On removing the limb bones, and White-winged Scoter (Melanitta de- they also found that the distal musculature glandi) to clarify our interpretation of the dried was “well enough preserved to warrant de- muscles of Camptorhynchus and some points scription,” The limb bones and muscles re- were also checked against the Common Eider moved from that specimen are the basis for this (Somateria mollissima). Bentz wrote the ini- study. Surprisingly, no broad comparative tial descriptions and Zusi made the illustra- survey of hindlimb myology of waterfowl has tions. The entire paper was reviewed and yet been published. Studies on a few species modified by both authors. One leg and one are those of Stolpe ( 1932), Miller ( 1937), wing were skeletonized; their counterparts Frantigek ( 1934) and Ruck ( 1949), and more are retained in alcohol. recently, Raikow ( 1970) analyzed diving We follow the myological nomenclature of adaptations in the stifftail ducks. Even fewer George and Berger (1966). Where their studies of forelimb myology are available. The terminology differs from that being developed most complete work is still that of Fiirbringer by the International Committee on Avian (1888), who dealt mainly with the shoulder Anatomical Nomenclature, we have added the and proximal portion of the wing. Brief de- new name in parentheses. The new terms have scriptions of wing muscles in a few species already been employed in certain studies and a detailed analysis of their functions in (Raikow 1976, 1977). We use the terms relation to flight were presented by Sy ( 1936). “major digit” and “minor digit” for wing Lacking broadly comparative information on digits II and III, and “major metacarpal” anatid myology we made no systematic com- and “minor metacarpal” for metacarpals II and parison of the Labrador Duck with other III, respectively. The term “alular phalanx” species; by contrast our comparison of the refers to the pollex. The directional terms cleaned limb bones with skeletons in the “dorsal” and “ventral,” “cranial” and “caudal” Smithsonian Institution and with informa- as applied to the forelimb, refer to the hori- tion presented by Woolfenden (1961) pro- zontally extended wing. vided some taxonomic clues that conclude this paper. MUSCLES OF THE FORELIMB Only the distal half of each humerus was M. biceps brachii (Not shown). This muscle present and only the distal muscles remained inserts by two parallel tendons that pass dor-

[4071 408 RICHARD L. ZUSI A?rTD G. D. BENTZ

OS ulnare

FIGURE 1. Ventral views of left forearm of Camntorhynchus.- ,~ (A and B) Superficial muscles; M. pronator superficialis removed in A. (C) Deep muscles. sal to M. brachialis. One inserts on the proxi- muscle arises by a strong tendon from the mocranial surface of the ulna. The other in- medial surface of the distal end of the humerus serts on the proximoventral surface of the j-ust deep and slightly proximal to the origin radius and sends a branch to the distal end of the humerocarpal band (h c). The fan- of the first tendon and the adjacent portion shaped belly passes distally to a fleshy in- of the ulna. sertion on the ventral surface of the proximal M. brachialis (Fig. 1C; b). This muscle has two-thirds of the radius. a fleshy origin on the distal end of the humerus Ad. flexor digitorum superficialis (Figs. lA, just proximal to the condyles. The fibers of 3A, 4C; f d s). This muscle arises by a short the belly pass distally along the cranial border tendon from the medial condylc of the hu- of the ligamenturn collaterale ventrale (1 c v) merus and is completely cnsheathed by the and insert fleshy on the ventral surface of the humerocarpal band. The spindle-shaped belly proximal end of the ulna. Its insertion is deep passes distally and ends on a narrow tendon to the belly of M. entepicondyloulnaris. that passes into the hand in a shallow groove M. pronator superficiaks (Fig. 1B; p s). on the cranial surface of the OS ulnare. The This muscle arises by a stout tendon from a tendon attaches to the proximal end of the shallow depression near the medial epicondyle first phalanx of the major digit, encloses a of the humerus. The belly fans out to insert sesamoid, and continues distally to insert on by semitendinous fibers on the cranioventral the cranial surface of the proximal end of the surface of at least the proximal half of the second phalanx of the major digit, ventral to radius. the insertion of M. extensor indicis longus. M. pronator profundus (Fig. 1A; p p). This M. flexor digitorum profundus (Figs. lC, MYOLOGY OF THE LABRADOR DUCK 409

FIGURE 2. Dorsal views of left forearm of Campto~hynclaus. (A) Superficial muscles. ( B ) M. extensor metacarpi ulnaris removed from its common tendon of origin with M. anconeus. (C) Deep muscles.

3A, 4C; f d p). This large muscle lies super- muscle has a common tendinous origin with ficial to M. ulnimetacarpalis ventralis and M. pronator profundus from the medial epi- arises by two fleshy heads from the cranio- condyle of the humerus. The belly fans out ventral surface of the ulna. The belly extends caudodistally and inserts fleshy on the ven- most of the length of the forearm and ends tral surface of the proximal one-fourth of the on a strong tendon that passes craniad to the ulna, ventral and caudal to the insertion of OS ulnare, around the pisiform process of the M. brachialis. George and Berger (1966: carpometacarpus, and into the hand. The 354) referred to this muscle as the “gallina- tendon passes along the cranioventral edge ceous” muscle, stating that it was known only of the carpometacarpus where it gradually in kiwis ( Apteryx), the Galliformes and tina- crosses the tendon of M. flexor digitorum mous. It is clearly present in Camptorhynchus superficialis caudally. At the distal end of and we found it also in the other ducks we ex- the first phalanx of the major digit the tendon amined. curves abruptly cranially and ventrally to M. flexor carpi ulnaris ( Fig. 1A; f c u) . This pass through a fibrous loop (not shown) and is the most caudal muscle on the ventral side an adjacent bony loop (not shown) on the of the wing. It arises by a strong tendon from proximocranial edge of the second phalanx. the distal end of the medial condyle of the From this loop the tendon continues along humerus, passes caudal and lateral to a large the cranioventral edge of the second phalanx sesamoid and gives rise to a strong, tendinous to insert on the proximoventral edge of the belly. The sesamoid is anchored by ligaments tiny third phalanx. to the medial condyle of the humerus and M. entepicondyZouZnu& (Fig. 1C; e). This to the olccranon process of the ulna. The 410 RICHARD L. ZUSI AND G. D. BENTZ

A B

FIGURE 3. Muscles of the wrist and manus of the left wing of Camptorhynchus. (A) Ventral view. (B) Dorsal view. Tendon of M. extensor indicis longus crosshatched for clarity. tendon of origin extends distally through the of insertion. This tendon encloses the patella center of the circumpennate belly, sending ulnaris just before it inserts on the coronoid fibers to the superficial ensheathing aponeuro- process of the ulna. A thin sheet of tendinous sis that becomes the tendon of insertion. The fibers connects the two tendons of insertion superficial aponeurosis is developed most and attaches on the ulna between them. strongly along the cranial edge of the belly. M. extensor metacarpi radialis (Figs. 2A, The 45 mm-long belly extends three-fourths 3A, B; e m r). This large muscle consists of the length of the forearm and ends on a strong two parts. The main part arises by both fleshy tendon that inserts on the proximal surface of and tendinous fibers from the lateral aspect the OSulnare. Additional fibers attached along of the distal end of the humerus just proximal the caudal surface of the main belly but their to the origin of M. supinator. The belly ex- connections to secondary feathers were not tends most of the length of the forearm and present. ends on a strong tendon that inserts on the M. ulnimetacarpalis ventralis ( M. ulnometa- extensor process of the carpometacarpus. The carpalis ventralis) (Figs. lC, 3A; u v). The second part begins as a tendon that arises bipennate belly of this muscle has a fleshy from the proximal portion of the caudal edge origin on the ventral surface of the distal half of the main tendon. This separate tendon of the ulna. The short, strong tendon of in- passes distally and gives rise to a spindle- sertion passes deep to a ligamentous band and shaped belly. The latter ends on a narrow inserts on the craniodorsal surface of the carpo- tendon that rejoins the main tendon prior to metacarpus proximal to the level of the ex- its insertion on the carpometacarpus. tensor process. M. extensor metacarpi ulnaris (Figs. 2A, M. triceps brachii (M. humerotriceps plus 3B; e m u). This muscle has its origin by two M. scapulotriceps) (Fig. 2A; ht, st). As in separate tendons. The larger of these arises other birds, this muscle is composed of two from the lateral surface of the ectepicondyle parts. Only the distal 10 mm of the tendon of the humerus, while the smaller arises from of insertion of M. humerotriceps remained on from the distal edge of the ectepicondyle. the specimen. The tendon passes between the These tendons shortly fuse to form a common lateral and medial condyles of the humerus, tendon of origin for both M. extensor meta- ventral to a large sesamoid, the patella ulnaris, carpi ulnaris and M. anconeus. A small ten- and inserts in a shallow depression on the dinous ulnar anchor (u a) arises from this olecranon process of the ulna. M. scapulotri- common tendon of origin; it passes caudally ceps was also represented only by its tendon and inserts on the ulna distal to the ulnar MYOLOGY OF THE LABRADOR DUCK 411

anchor of M. extensor digitorum communis. ei I i P i d M. extensor metacarpi ulnaris arises from the distalmost portion of the common tendon at about the distal limit of the ulnar anchor. The large belly extends three-fourths the length of the ulna and ends on a tendon that passes deep to a ligamentous loop at the distal end of the ulna. The tendon inserts on the caudodorsal edge of the proximal end of the shaft of the major metacarpal. a i M. anconeus (M. ectepicondylo-ulnaris) I jP (Figs. 2A, B; a). This fan-shaped muscle arises from the ventral surface of the proximal portion of the common tendon of origin for this muscle and M. extensor metacarpi ulnaris. The muscle extends distally and inserts fleshy fd3 ’ on all but the distal few millimeters of the proximal two-thirds of the craniodorsal surface of the ulna. M. extensor digitorum communis (Figs. 2A, 3B; e d c). This long, narrow muscle arises by a strong tendon from the lateral epicondyle of the humerus superficial to ’ the origin of M. supinator. A small tendinous ulnar anchor in this muscle arises from the tendon of origin, f d3 passes caudally, and inserts on the ulna proximal to, and parallel with, the ulnar anchor FIGURE 4. Muscles of the left manus of Campto- of M. extensor metacarpi ulnaris. The large rhynchus. (A) Dorsal view. ( B and C) Ventral views. belly extends two-thirds the distance down the (C) Tendon of M. flexor digitorum superficialis forearm and ends on a well-developed tendon. black; tendon of M. flexor digitorum profundus crosshatched; tendon of M. abductor indicis dashed. The latter passes over the distal end of the ulna dorsally through a fibrous loop and then divides near the proximal end of the carpometa- radiale. The tendon continues through a small carpus. One branch passes cranially and inserts cartilage that is bounded by the carpometa- on the caudal surface of the alular pha- carpus, the radiale, the ulnare, and the distal lanx about 5 mm from the proximal end of the end of the ulna and passes into the hand. The bone. The longer branch continues distally tendon proceeds cranially along the dorsal sur- and curves caudally in a groove on the dorsal face of the carpometacarpus and inserts on the surface of the carpometacarpus. It then passes cranial surface of the proximal end of the deep to a ligamentous loop at the distal end of second phalanx of the major digit. Associated the carpometacarpus and turns cranioventrally with the main tendon is a flat, ligamentous to insert on the cranioventral corner of the band that passes distally from the wrist carti- proximal end of the first phalanx of the major lage caudal to the main tendon. This band digit. fuses with the main tendon just before it in- M. supinator (Fig. 2A; s). This muscle arises serts. The main tendon lies in a groove along by a well-developed tendon from a shallow the cranial edge of this band. depression near the lateral epicondyle of the As noted by George and Berger (1966: humerus just deep to the tendon of origin of 367), a distal head may also be present. In M. extensor digitorum communis. The fan- Camptorhynchus the distal head lies caudal shaped belly passes distally to a fleshy inser- to the belly of M. extensor pollicis brevis. It tion on the craniodorsal surface of the prox- arises fleshy from the caudodorsal surface imal half of the radius. of the proximal end of the major metacarpal M. extensor indicis longus (M. extensor and from a ligamentous capsule that attaches longus digiti majoris) (Figs. 2A, C; 3B; 4A, to the caudodorsal surface of the OS radiale. C; e i 1). The slender belly of this muscle The small, spindle-shaped belly ends on a arises by both fleshy and tendinous fibers thread-like tendon. We could not trace this from most of the caudal surface of the radius. tendon to the main tendon of insertion. The belly ends on a tendon that passes distally M. extensor pollicis longus (M. extensor between the distal end of the ulna and the OS longus alulae) (Figs. lC, 2A, C, 3B; e p 1). 412 RICHARD L. ZUSI AND G. D. BENTZ

As in most birds, this muscle has two heads of M. abductor indicis (M. abductor digiti origin. The ulnar head has a fleshy origin majoris) (Figs. 3A, B, 4B, C; a i). This along the proximal 2-3 mm of the cranial sur- muscle arises fleshy from the carpometa- face of the ulna. The radial head arises carpus beginning at the level of the pisiform fleshy from the caudal surface of the prox- process where it lies deep to M. flexor pollicis, imal end of the radius and, more distally, from and, more distally, from the cranial surface of the caudodorsal surface of the radius. These the major metacarpal. The belly ends on a heads join at about the distal end of the prox- strong tendon that inserts on the cranial sur- imal one-third of the forearm. The common face of the proximal end of the first phalanx belly passes distally and ends on a strong, of the major digit. The insertion (not shown) narrow tendon that inserts on the dorsal sur- lies between the tendons of insertion of M. ex- face of the distal end of the tendon of inser- tensor indicis longus and M. flexor digitorum tion of M. extensor metacarpi radialis. superficialis. M. ulnimetacarpalis dorsalis (M. ulnom&a- M. interosseus dorsalis ( M. interosseous carpa& dorsalis) (Fig. 3B; u d). This well- dorsalis) (Fig. 4A; i d). This bipennate developed muscle arises by a short tendon muscle has a fleshy origin along the dorsal from the dorsal surface of the distal end of the surface of the proximal portion of the carpo- ulna. The belly passes distally a few milli- metacarpus and the facing surfaces of the meters to a fleshy insertion on the caudo- major and minor metacarpals. The tendon dorsal surface of the proximal end of the minor of insertion proceeds through a fibrous canal metacarpal, opposite the insertion of M. ex- at the distal end of the carpometacarpus, tensor metacarpi ulnaris. The insertion ex- passes along the dorsal surface of the first tends from near the proximal end of the minor phalanx in a shallow groove, and attaches on metacarpal to the curve of the dorsal edge of the craniodorsal corner of the second phalanx that bone. of the major digit. A cartilaginous thickening M. extensor pollicis brevis (M. extensor of the tendon occurs at the interphalangeal hrevis alulae) (Fig. 3B; e p b). This short, joint. From this thickening the slender tendon fan-shaped muscle arises fleshily from the passes distally along the craniodorsal edge of dorsal surface of the extensor process of the the second phalanx to insert on the proximo- carpometacarpus. The fibers converge onto dorsal edge of the small third phalanx. a strong tendon that inserts on the proximo- M. interosseus palmark (M. interosseous cranial corner of the alular phalanx. ventralis) (Figs. 3A, 4A, B; i p). This muscle M. abductor pollicis (M. abductor alulae) is as well-developed as M. interosseus dorsalis. (Fig. 3A; ab p). This small, spindle-shaped The bipennate belly occupies the intermeta- muscle arises from the ventral edge of the carpal space and ends on a tendon that passes tendon of insertion of M. extensor metacarpi to the dorsal side of the wing through a bony radialis. The muscle has a fleshy insertion canal at the distal end of the carpometacarpus. along most of the cranioventral surface of the The insertion is on the caudal edge of the alular phalanx. The muscle is strongly unipen- second phalanx of the major digit. nate with many fibers passing between paral- M. flexor digiti III (M. flexor digiti minoris) lel aponeuroses of origin and insertion. (Figs. 3A, 4B, C; f d 3). This muscle arises M. adductor pollicis (M. adductor alulae) fleshy from most of the caudal surface of the (Fig. 3B; ad p). This short block of muscle carpometacarpus. The proximal portion of arises by semitendinous fibers from the cranio- the belly is bipennate, but beyond the level of ventral surface of the proximal portion of the insertion of M. ulnimetacarpalis dorsalis, the major metacarpal. The belly passes cranially fiber arrangement is unipennate. The inser- and inserts on the caudal surface of the alular tion is by a short tendon as well as by fleshy phalanx just ventral to the branch tendon of fibers on the caudal surface of the proximal insertion of M. extensor digitorum communis. end of the minor digit. M. flexor pollicis (M. flexor alulae) (Fig. 3A; f p). This small muscle arises by both MUSCLES OF THE HINDLIMB fleshy and tendinous fibers from a small de- M. gastrocnemius (Fig. 5D; g). The tendon pression proximal and cranial to the pisiform of this muscle becomes thickened and slightly process of the carpometacarpus, caudal to the wider as it passes over the caudal surface of belly of M. abductor pollicis. The fleshy the tibia1 cartilage (t c). The insertion is fibers attach to a short tendon that inserts on on the caudal surface of the hypotarsus along the ventral corner of the proximal end of the most of its length. alular phalanx. M. tibialis anterior (M. tibia&s cranialis) MYOLOGY OF THE LABRADOR DUCK 413

t a edl pb

ad 2 a4

FIGURE 5. Muscles of the tarsometatarsus of Camptorhynchus. (A) Cranial view, right leg. (B) Caudo- lateral view, left leg. (C) Medial view, left leg; tendon of M. extensor digitorum longus displaced. (D) Lateral view of ankle joint, left leg; tendon of M. gastrocnemius displaced.

(Fig. 5A; t a). The tendon of this muscle three foretoes. Owing to the brittle condition passes deep to the ligamentum transversum of the specimen the pattern of insertion of (1 t) lateral to the tendon of M. extensor this tendon could not be determined with con- digitorum longus. It widens slightly as it fidence. continues distally and crosses the intertarsal M. perowus longus (M. fibularis longus) joint. The tendon tapers slightly, then (Fig. 5D; p 1). The tendon of this muscle broadens and divides just before it inserts passes along the lateral surface of the tibio- on the cranial surface of the proximal end tarsus and divides near the distal end of that of the tarsometatarsus. bone. One branch passes caudally and fuses M. extensor digitorum longus (Figs. 5A, C; with a dense fascial sheet on the lateral sur- e d 1). The tendon of this muscle passes face of the tibia1 cartilage. The main tendon through a bony canal that is deep to the liga- crosses the intertarsal joint and fuses with the mentum transversum. It then proceeds dis- tendon of M. flexor perforatus digiti III near tally medial to the tendon of M. tibialis an- the distal end of the proximal one-third of the terior and passes through a second fibrous loop tarsometatarsus. on the cranial surface of the proximal end of M. peroneus brevis (M. fibularis brewis) the tarsometatarsus. At the distal end of the (Figs. 5A, D; p b). The tendon of this muscle tarsometatarsus the tendon divides, sending passes through a fibrous canal on the lateral a branch to the dorsal surface of each of the surface of the distal end of the tibiotarsus 414 RICHARD L. ZUSI AND G. D. BENTZ

fdl

f d I

fPP2 C

FIGURE 6. Plantar tendons of right foot of Campto~hynchus. (A) Ventral view of digit IV, tendon of M. flexor perforatus digiti IV crosshatched. (B) Lateral view of digit IV. (C) Lateral view of digits II and III, tendons displaced for clarity; branch tendons of M. flexor digitorum longus black.

and crosses the intertarsal joint. The insertion M. flexor perforans et perforatus digiti II is on the caudolateral surface of the proximal (Figs. 6C, 7; f p p 2). The tendon of this end of the tarsometatarsus. muscle passes through a caudomedial canal M. flexor perforans et perforatus digiti III of the tibia1 cartilage and along a tendinous (Figs. 6C, 7; f p p 3). The tendon of this groove on the caudomedial surface of the muscle passes through a large, caudolateral hypotarsus. It proceeds distally along the canal of the tibia1 cartilage and along the tarsometatarsus and divides at about the mid- hypotarsus in company with the tendons of point of the first phalanx, allowing for the M. flexor perforatus digiti III and M. flexor passage of the branch tendon of M. flexor perforatus digiti IV. It then receives a small digitorum longus. The tendon passes distally tendinous branch from the tendon of M. ventral to the branch tendon of M. flexor flexor perforatus digiti III and continues dis- digitorum longus and inserts on the lateral tally along the caudal surface of the tarsometa- and medial surfaces of the proximal end of tarsus. The tendon passes along a cartilaginous the second phalanx of digit II. pad at the base of digit III, perforates the M. flexor perforatus digiti IV (Figs. 6A, B, tendon of M. flexor perforatus digiti III, and 7; f p 4). The tendon of this muscle passes then divides at the distal end of the first through a large caudolateral canal of the tibia1 phalanx, allowing for the passage of the cartilage in company with the tendons of M. branch tendon of M. flexor digitorum longus. flexor perforatus digiti III and M. flexor The insertion is on the lateral and medial sur- perforans et perforatus digiti III. It then passes faces of the proximal end of the third phalanx along a groove on the caudolateral surface of digit III. of the hypotarsus. It continues distally along MYOLOGY OF THE LABRADOR DUCK 415 the caudal surface of the tarsometatarsus and becomes thickened as it passes ventral to a cartilaginous pad at the base of the fourth toe. The tendon divides at the proximal end of the first phalanx. The two most proximal branches insert, respectively, on the lateral surface of the distal end of the first phalanx and on the lateral surface of the distal end of the second phalanx. The medial and most distal branch passes dorsal to the branch of M. flexor digitorum longus and inserts on the plantar surface of the proximal end of the fourth phalanx. M. flexor perforutus digiti III (Figs. SD, 6C, 7; f p 3). The tendon of this muscle passes through the tibia1 cartilage and along the hypotarsus in company with the tendons of M. flexor perforatus digiti IV and M. flexor FIGURE 7. Left hypotarsus and tibia1 cartilage of Camptorhynchus; semidiagrammatic. In life, tibia1 perforans et perforatus digiti III. It then re- cartilage would be proximal to (superimposed on) ceives the main tendon of M. peroneus longus, hypotarsus. Dotted line represents a sheet of connec- and shortly sends a small branch to the tendon tive tissue. Black ovals represent tendons in relation to of M. flexor perforans et perforatus digiti III. hypotarsus; open ovals show their relations to tibia1 The main tendon then thickens and divides cartilage. ( 1) M. flexor hallucis longus: (2) M. flexor -perforatus digiti III (above), hi: flexor ’ per- allowing for the passage of the tendon of M. foratus digiti IV (lower left), M. flexor perforans et flexor perforans et perforatus digiti III and the perforatus digiti III (lower right); (3) M. flexor branch tendon of M. flexor digitorum longus. perforatus digiti II; (4) M. flexor digitorum longus; The main insertion is on the medial and lat- (5) M. flexor perforans et perforatus digiti II. eral surfaces of the proximal end of the second phalanx of digit III. Both branches are also tightly bound to the distal end of the first of the Oldsquaw, the scoter, and the eider phalanx. and they are unknown in other birds. Most It was difficult to determine whether or not tendons of the left foot except that of M. flexor the tendinous connection between the tendons digitorum longus were destroyed in cleaning of M. flexor perforans et perforatus digiti III the bones before we first saw the loops. A and M. flexor perforatus digiti III was the small loop on one branch of the tendon of vinculum as described by Hudson (1937). M. flexor digitorum longus of that foot, how- Such a structure has been found in ducks ever, suggested that loops on other tendons (George and Berger 1966:433; Raikow 1970: may have been present, as in the right foot. Fig. 17). An examination of the feet (stuffed and re- M. flexor per/or&us digiti ZZ (Figs. 6C, 7; sewn by Humphrey and Butsch) of the study f p 2). The tendon of this muscle passes skin revealed small holes in the podothecae through a central canal of the tibia1 cartilage of both feet in precisely the positions to be and through a central groove of the hypo- expected if a needle or wire had been passed tarsus. It proceeds down the tarsometatarsus through the feet (and tendons) during the lateral to the tendon of M. flexor perforans et initial preparation of the specimen. We be- perforatus digiti II. After becoming thickened, lieve that the loops in the tendons are artifacts it inserts on the proximolateral corner of of preparation. phalanx one of digit II where it is bound to a M. flexor digitorum longus (Figs. 6A, B, C, cartilaginous pad associated with that digit. 7; f d 1). The tendon of this deep flexor The tendon is neither perforated nor does it muscle passes through a canal of the tibia1 cartilage and then through the medial canal of perforate any other tendon. the hypotarsus. It then passes distally along When we dissected the tendons of M. flexor the caudal surface of the tarsometatarsus, re- perforatus digiti IV, M. flexor perforatus digiti ceives the tendon of M. flexor hallucis longus, III, and M. flexor perforans et perforatus digiti and divides at a point about half the distance III, we noticed a loop in each tendon near the between the level of the hallux and the distal base of the toes. The presence of these loops end of the tarsometatarsus, sending branches in the flexor tendons of both feet was initially to all of the foretoes. At the distal end of the puzzling as we found none in a specimen each tarsometatarsus, each branch tendon passes 416 RICHARD L. ZUSI AND G. D. BENTZ ventral to a cartilaginous pad and is held in from the hypotarsus to the trochleae. Prox- place by a sheath of connective tissue that at- imally the belly is fan-shaped, its fibers con- taches along the lateral and medial edges of verging on a broad, superficial aponeurosis. each pad, as well as the proximoventral ridges Distally, the bipennate belly widens again be- of each basal phalanx. The branch to digit fore giving rise to a tendon that inserts on the II perforates the tendon of M. flexor perforans ventrolateral surface of the proximal end of et perforatus digiti II and continues distally the first phalanx of digit IV. along the plantar surface of the second pha- M. abductor digiti II (Fig. 5C; ab 2). This lanx past its distal end. The branch to digit small, fan-shaped muscle arises fleshy from III perforates the tendon of M. flexor per- the distomedial surface of the tarsometatarsus foratus digiti III and continues distally to between the hallux and the medial trochlea. perforate the tendon of M. flexor perforans et The belly ends on a stout tendon that inserts perforatus digiti III. The tendon proceeds on the medial surface of the proximal end of along the plantar surface of digit III beyond the first phalanx of digit II. the distal end of the third phalanx. The branch M. extensor prop&s digiti III (Fig. 5A; e to digit IV lies in a groove on the lateral sur- p 3). Small and fan-shaped, this muscle has face of the tendon of M. flexor perforatus a fleshy origin from the cranial surface of the digiti IV at the proximal end of the basal distal one-third of the tarsometatarsus. The phalanx. The tendon passes between the short tendon passes over the trochlea and in- distal two branches of the tendon of M. serts on the dorsal surface of the proximal flexor perforatus digiti IV and proceeds dis- end of the first phalanx of digit III. tally, ventral to the most medial branch of M. extensor brevis digiti IV (Fig. 5A; e b that tendon. The tendon continues along the 4). This bipennate muscle arises by both plantar surface of digit IV past the distal end fleshy and tendinous fibers from the cranial of the fourth phalanx. The ungual phalanges surface of the tarsometatarsus at the level of and insertions of the branch tendons were the insertion of M. tibialis anterior. The belly missing. Accessory vincula could not be ends on a tendon that passes through the found. distal foramen of the tarsometatarsus and in- M. flexor hallucis longus (Fig. 7). In serts on the dorsal surface of the proximome- Camptorhynchus the tendon of this muscle dial corner of the first phalanx of digit IV. was present only in its role of assisting the We were unable to find M. flexor hallucis tendon of M. flexor digitorum longus. A brevis, M. lumbricalis, and the tendon of in- branch to the hallux could not be found. In sertion of M. plantaris in our specimen of Somateria mollissima we found that the ten- Camptorhynchus. This was probably due to don passed through a lateral canal of the tibia1 the dried and brittle condition of the muscles. cartilage and through the lateralmost groove of the hypotarsus. DISCUSSION M. extensor hallucis longus (Fig. 5C; e h 1). This small muscle arises fleshy from the me- The presence of M. entepicondyloulnaris in dial surface of the tarsometatarsus just prox- ducks was first reported by Sy ( 1936), who imal to the midpoint of that bone. The fibers described and illustrated it in Cusarca (= of the belly converge on a short tendon that the Ruddy Sheld-Duck, Tndorna ferruginea? ) . inserts on the dorsal surface of the proximal Its presence also in Camptorhynchus labra- end of the hallux. dorius, Melanitta deglundi, Clangula hyemulis, M. adductor digiti II (Fig. 5B; ad 2). This and Somateria mollissima, demonstrated here, small, bipennate muscle has a fleshy origin suggests that this muscle occurs widely in on the caudal surface of the tarsometatarsus the Anatidae. The muscle is presently known distal to the level of the hallux and medial only in Apteryx, Tinamidae, Calliformes, and to the belly of M. abductor digiti IV. The Anatidae. Although it appears to be a primi- belly ends on a tendon that passes under two tive feature in birds, its taxonomic significance strong ligaments and inserts on the proximo- cannot be determined without documenting medial surface of the first phalanx of digit its presence or absence in other avian families. II. Statements about the true extent of muscle Our study sheds no light on the affinities of origin are tenuous in small muscles such as the Labrador Duck owing to the lack of any this, owing to shrinkage from drying. comparative study of the myology of the sea M. abductor digiti IV (Fig. 5B; a 4). This ducks. Several features of the carpometa- muscle arises from a depression in the caudal carpus and tarsometatarsus, however, provide surface of the tarsometatarsus that extends taxonomic clues. Woolf enden ( 1961: 32-33 ) MYOLOGY OF THE LllBRADOR DUCK 417 pointed out that a basic difference in the shape that Camptorhynchus “seems to be about of the process of metacarpal I divides the sea halfway between the eiders and the Old- ducks into two groups: ( 1) Bucephala and squaw.” In the Check-list of North American the mergansers, and (2) the eiders, scoters, Birds (A. 0. U. 1957), the Labrador Duck is Histrionicus and Clangula. In this character placed between the Harlequin Duck and the Camptorhynchus clearly falls within the sec- eiders, and Palmer (1976) put it between the ond group. We have found that the position scoters and the Harlequin Duck. Humphrey of the nutrient foramen of the tarsometatarsus, and Butsch (1958) put Camptorhynchus in as seen just distal to the hypotarsus, also the Mergini between Melanitta and Clangula, separates the two groups of sea ducks. In the and they removed the eiders from that tribe. first group the foramen lies lateral to the long Based on an illustration of the sternum in axis of the lateral groove of the hypotarsus Rowley (1877), Woolfenden (1961:45) stated (housing the tendon of M. flexor hallucis that “the sternum resembles that of the eiders longus); in the second, the foramen lies on or in that the posterior lateral processes are wide, medial to the axis of that groove. Again, and in line with the long axis of the element, Camptorhynchus resembles the eiders, scoters, and it lacks the basal curvature possessed by and their relatives in this respect. the scoters. However, the sternum appears Woolfenden (1961:85) listed several char- less specialized than in the eiders, for the acters of the tarsometatarsus by which eiders posterior lateral processes approach the xiphi- could be distinguished from other ducks; we sternum, as in Histrionicus.” We found the found that Camptorhynchus agrees well with sternum of the Labrador Duck to most closely those given for eiders. However, we did not resemble that of the Stellers’ Eider (Poly- find the curvature of the external edge of the sticta stelleri). From a description of the shaft to be notably different between eiders trachea by Wilson (1829), Johnsgard (1965: and scoters. Spreading of the trochleae was 270) concluded that the “asymmetrical and not easily discernible except through the shape osseus bulla is unlike that of the scoters, and of the space between the trochleae for digits the only other sea ducks with such bullae are III and IV. In scoters, the opposite sides of the eiders and the Harlequin Duck. This these trochleae tend to be straight and paral- suggests that the Labrador Duck might pro- lel, enclosing a relatively narrow space; in vide an evolutionary link between the eiders eiders and Camptorhynchus, the opposite sides and such other sea ducks as the harlequin and are each somewhat concave, enclosing a more the scoters.” The presence of skeletal char- oval and wider space. In Camptorhynchus acters unique to eiders and the Labrador the minimum width of the shaft was 9.0% of Duck leads us to regard the eiders as the the total length, near the middle of the range nearest living relatives of the Labrador Duck. (8.5-9.8%) given by Woolfenden for eiders. Woolfenden ( 1961:33) also listed charac- LITERATURE CITED ters of the carpometacarpus that he believed separated the eiders from scoters and the A~~ERICAN ORNITHOLOGISTS ’ UNION. 1957. Check- Harlequin Duck ( Histrionicus histrionicus). list of North American birds. Fifth ed. Am. Ornithol. Union, Baltimore. Of these we found the more distal attachment DELACOUR, J. AND E. MAYR. 1945. The Family of M. extensor metacarpi ulnaris (his “flexor”) Anatidae. Wilson Bull. 57:3-55. and the slight curvature of metacarpal II from FRANTISEK, J. 1934. Les muscles de lextrkmite’ medial (our ventral) view to be generally posterieure chez loie’ et chez le canard. Biol. characteristic of the eiders, although each fea- Spisy Vys. Sk. ZvBrolkkafskk. Brno, &r. 13: l-20. ture is variable in both eiders and scoters. F~~RBRINGER, M. 1888. Untersuchungen zur Mor- Camptorhynchus matches the eiders in both phologie und Systematik der Vogel, zugleich ein features. Histrionicus and Clangula differ Beitrag zur Anatomie der Stiitz- und Bewegung- from Camptorhynchus in having a straight sorgane. Van Holkema, Amsterdam. metacarpal II. In Camptorhynchus we also GEORGE, J. C. AND A. J. BERGER. 1966. Avian myology. Academic Press, New York. found that the dorsal edge of metacarpal III HUDSON, G. E. 1937. Studies on the muscles of curves ventrally (from caudal view) as it ap- the pelvic appendage in birds. Am. Midl. Nat. proaches its proximal junction with meta- 18:1-108. HUIIPHREY, P. S. AND R. S. BUTSCH. 1958. The carpal II. In Histrionicus, Clangula, and most anatomy of the Labrador Duck, Camptorhynchus specimens of scoters, the proximodorsal edge Zubradorius ( Gmelin). Smithson. Misc. Collect. runs almost parallel to the dorsal edge of meta- 135 ( 7 ) : l-23. JOHNSGARD, P. A. 1965. Handbook of waterfowl carpal II. behavior. Cornell Univ. Press. Ithaca, New Delacour and Mayr (1945:33) remarked York. 418 RICHARD L. ZUSI ANI) G. D. BENTZ

MILLER, A. H. 1937. Structural modifications in epl 14. extensor pollicis longus the Hawaiian Goose ( Nesochen sandvicensis ) . f c u M. flexor carpi ulnaris A study in adaptive evolution. Univ. Calif. fd3 M. flexor digiti III Publ. Zool. 42:1-80. fdp M. flexor digitorum profundus PAL~XER, R. 1976. Handbook of North American fds M. flexor digitorum superficialis birds. Vol. 3. Yale Univ. Press, New Haven. fP M. flexor pollicis RAIKOW, R. J. 1970. Evolution of diving adapta- hc humerocarpal band tions in the stifftail ducks. Univ. Calif. Publ. ht M. humerotriceps Zool. 94: l-52. id M. interosseus dorsalis RAIKOW, R. J. 1976. Pelvic appendage myology of ip M. interosseus palmaris the Hawaiian honeycreepers ( Drepanididae ) . lcv ligamentum collaterale ventrale Auk 93:774-792. PP M. pronator profundus RAIKOW, R. J. 1977. Pectoral appendage myology Ps M. pronator superficialis of the Hawaiian honeycreepers ( Drepanididae) . S M. supinator Auk 94:331-342. st M. scapulotriceps ROWLEY, G. D. 1877. Somuteria lubrudoria (J. F. II a ulnar anchor Gmelin ) . Ornithological Miscellany 2 :205-223. ud M. ulnimetacarpalis dorsalis RUCK, P. R. 1949. Studies on the muscles of the 11 v M. ulnimetacarpalis ventralis pelvic appendage in certain anseriform birds. Unpubl. M.S. Thesis. Pullman: State College HINDLIMB of Washington. a4 M. abductor digiti IV STOLPE, M. 1932. Physiologisch-anatomische Unter- ab 2 M. abductor digiti II suchungen iiber die hintere Extremitat der Vagel. ad 2 M. adductor digiti II J. Ornithol. 80: 161-247. eb4 M. extensor brevis digiti IV SY, &I. 1936. Funktionell-anatomische Untersuchun- edl M. extensor digitorum longus gen am Voeelfliieel. 1. Ornithol. 84:199-296. ehl M. extensor hallucis longus WILSON, A. 182”9. American ornithology. Vol. 3. ep3 M. extensor proprius digiti III Constable & Co., Edinburgh. fdl M. flexor digitorum longus WOOLFENDEN, G. E. 1961. Postcranial osteology fP2 M. flexor perforatus digiti II of the waterfowl. Bull. Fla. State Mus. 6:1-129. fP3 M. flexor perforatus digiti III fP4 M. flexor perforatus digiti IV fPP2 M. flexor perforans et perforatus digiti II GLOSSARY OF ABBREVIATIONS fPP3 M. flexor perforans et perforatus digiti III M. gastrocnemius FORELIMB l”t ligamentum transversum pb M. peroneus brevis a M. anconeus ph 4 phalanx 4 ab P M. abductor pollicis PI M. peroneus longus ad P M. adductor pollicis t a M. tibialis anterior ai M. abductor indicis tc tibia1 cartilage b M. brachialis e M. entepicondyloulnaris edc M. extensor digitorum communis National Museum of Natural History, Smithsonian eil M. extensor indicis longus Institution, Washington, DC. 20560. Present address emr M. extensor metacarpi radialis of second author: Mount Vernon College, Washing- e m u M. extensor metacarpi ulnaris ton, D.C. 20007. Accepted for publication 24 Febru- epb M. extensor pollicis brevis ary 1978.