Wing myology of Caracaras (Aves, Falconiformes): muscular features associated with flight behavior

177 ISSN 1864-5755 68 (2): 177 –190 15.8.2018 © Senckenberg Gesellschaft für Naturforschung, 2018. Wing myology of Caracaras (Aves, Falconiformes): muscular features associated with flight behavior Mariana Beatriz Julieta Picasso 1 * & María Clelia Mosto 1 1 Museo de La Plata-Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata – CONICET. Paseo del Bosque s/n, La Plata (1900), Buenos Aires, Argentina — *corresponding author: [email protected] Accepted July 12, 2018. Published online at www.senckenberg.de/vertebrate-zoology on July 27, 2018. Editor in charge: Martin Päckert Abstract Caracaras (Aves, Falconiformes, Falconidae) are Neotropical diurnal raptors that belong to the subfamily Polyborinae. The forelimb myology of this group has not been comprehensively studied or compared with that of other Falconidae. Thus, the aims of this study were i) to describe the forelimb muscles of two species of Polyborinae (Caracara plancus and Milvago chimango), ii) to explore the possible relationship between muscular features and their function in flight behavior and iii) to compare the muscular features of these species with those of species of the subfamily Falconinae. To this end, the forelimb muscles of C. plancus (n = 4) and M. chimango (n = 4) were dissected. Additonally, to complement this data set, two specimens of M. chimachima were dissected. The mass of each muscle of one wing and its percentage with respect to the body mass were obtained. A total of 45 muscles were identified, and differences with respect to Falconinae were related to the presence of single or additional bellies. The total forelimb muscle mass represented between 7.68 and 10.26 % of the body mass. The muscle pectoralis represented  5% of the body mass, followed by the muscles scapulohumeralis caudalis (0.64 – 0.79%), deltoideus major (0.43 – 0.53%), supracoracoideus (0.34 – 0.38%) and biceps brachii (0.26 – 0.39%). The high values of these muscles are in agreement with their important function: they are involved in the downstroke and upstroke phases of the flapping flight. On the other hand, the muscles that seemed to contribute little to the mechanical power for flight presented low values that ranged between 0.01 and 0.25%. Comparison of the forelimb muscles of caracaras with published data on Falconinae species suggests that their muscular features might be associated with their type of flight, which is more erratic and less powerful than that of Falconinae. Key words Forelimb morphology, Falconidae, Polyborinae. Introduction Since flight is a demanding mode of locomotion, the wings of flying birds have numerous anatomical features to meet this demand (Heers et al., 2016). These include a complex and varied morphology comprising many muscles (between 45 and 50) (GeorGe & BerGer, 1966; raikow, 1985), which generate and control their movements (Videler, 2006) and the different flight behaviors (e.g. flapping, gliding, hovering, etc.). Although the features of these muscles, i.e. number of bellies, relative development and mass, vary between taxa (Hartman, 1961; GeorGe & BerGer, 1966), this variability and its possible association with flight behavior have been scarcely investigated both in birds in general and particularly in Falconiformes (see Hartman, 1961; meyers, 1992a, b; CorVidae et al., 2006; Hertel, maldonado & sustaita, 2014; CanoVa et al., 2015a, b, c). Although the Falconidae have been classically grouped together with the Accipitridae (hawks, eagles, kites) due to their morphology, there is a general consensus that the Falconidae are phylogenetically distant from these other diurnal birds of prey (HaCkett, et al., 2008; JarVis et al., 2014; Prum et al., 2015). The family Falconidae consists of three subfamilies, Polyborinae Falconinae and Herpetotherinae, which show diversity in their locomotor behavior and diet. The Polyborinae (caracaras) are endemic to the New World and distinguished Picasso, M.B.J. & Mosto, M.C.: Wing myology of Caracaras (Aves, Falconiformes) 178 as ambulatory birds that mostly forage by walking on the ground and in which flight is not as important as in the other two families (Cade & diGBy, 1982; wHite, et al., 1994; FuCHs, et al. 2012). Moreover, the caracaras have an erratic and slow flight in which they alternate flapping and gliding (CaneVari et al., 1991; wHite et al., 1994). The caracaras also have a diverse diet: some genera like Daptrius and Ibicter are omnivorous and arboreal, whereas other genera, such as Milvago, Caracara and Phalcoboenus, are opportunistic, feeding on invertebrates, vertebrates, garbage and carrion (CaneVari et al., 1991; Grin, 2018). In contrast, the Falconinae (cosmopolitan falcons) have a more diverse and complex flight behavior: they hunt in flight at high speeds to strike their prey (mainly birds and insects) and some species can also hover or soar (wHite et al., 1994; sustaita, 2008). Finally, the Herpetotherinae (forest and laughing falcons) are secretive birds that inhabit the humid forests of the Neotropics and are poorly known (wHite et al., 1994). Despite these interesting flight variations, little is known about the forelimb myology of the Polyborinae, and previous research consists mainly on descriptive studies based on the Falconinae. BerGer (1956), studied the appendicular myology of Polihierax semitorquatus (Pygmy falcon), and described only 18 muscles of the wing. Jollie (1977), in his extensive study on birds of prey, briefly mentioned some muscles for the forelimbs of Falco sparverius (American kestrel) and Polyborus cheriway, with scarce information and few illustrations. meyers (1992a, 1996) studied the brachial and antebrachial muscles of Falco sparverius, being, to date, the most complete descriptive works on the forelimb myology of Falconidae. More recently, in a comparative framework with other non-Falconiformes bird species, CanoVa et al. (2015 a, b) studied some muscles of Falco tinnunculus. The only quantitative information regarding the mass of wing muscles was published by Hartman in 1961. However, these data do not refer to individual muscles, but to the entire wing, with the exception of the muscle pectoralis and the muscle supracoracoideus. Thus, to expand our knowledge on the forelimb myology of the Polyborinae, the aims of the present study were i) to describe, photograph and illustrate the forelimb muscles of three species of Polyborinae (Caracara plancus, Milvago chimachima and Milvago chimango), ii) to explore the possible relationship between the muscular features of these species and their function in flight behavior, and iii) to compare the muscular features of these species with those of species of the subfamily Falconinae. Materials and methods Specimens: Healthy and unsexed adults of Caracara plancus (crested caracara, n=4), Milvago chimango (chimango caracara, n=4) and Milvago chimachima (yellow headed caracara, n=2) were used. The specimens of C. plancus and M. chimachima were obtained from La Marcela farm (26°17035″S; 59°06067″W), Pirané, Formosa province, Argentina, with authorization of Ministerio de la Producción y Ambiente, Dirección de Fauna y Parques of Formosa Province (guía de tránsito nº 003384) during 2014. The specimens of M. chimango were obtained from Programa de Control de Aves en Rellenos Sanitarios y Areas Aledañas (ProCoA) in the province of Buenos Aires, Argentina, during 2013. This research complied with protocols approved by the animal care committee and adhered to the legal requirements of Argentina. Data collection: The body mass of each specimen was weighed with a digital scale, except for that of the two specimens of M. chimachima, which was taken from dunninG (2008). Then, the anterior corporal region was carefully separated from the rest of the body, without damaging the muscles. The hind limbs were studied in mosto et al. (2013; 2016). Each individual region was properly identified and stored in individual bags and frozen until it was studied. The left wing muscles were unilaterally dissected during the six months following storage. The wing muscles were defrosted, identified, photographed, carefully removed and weighed (both the fleshy and tendinous components) with a digital scale (with 0.01-g accuracy). The percentage of each muscle with respect to its body mass was calculated considering one wing. Also, the forelimb muscle mass was calculated as the sum of the individual muscles except the small muscles of the manus (mm. abductor digiti majoris, extensor brevis alulae, abductor alulae, flexor digiti minoris, flexor alulae, and adductor alulae), which give little mechanical power for flight (Biewener, 2011). Muscular mass data were explored considering the movements of the main bones and joints, including those of the muscles associated with the thoracic shoulder (ossa cinguli), the arm (humerus), the forearm (ulna and radius), the elbow (the juncture cubiti) and the wrist joint (juncture carpi). The main roles of the muscles during flight were determined following that described in the works of raikow (1985), dial (1992) and Vazquez (1995, Table 1). The muscular description is the same in the three species and only the differences among them are mentioned. The interpretations about muscle mass were based only on the data obtained for C. plancus and M. chimango, given that the data available are more complete. Similarly, the interpretation about the small muscles of the manus and digits was based on the complete data obtained for C. plancus. Because of the low number of specimens of M. chimachima, the muscle mass data are provided only as complementary data. The mm. subcoracoideus and subscapularis were weighed together because of the common tendon of insertion, and the small m. propatagialis p. caudalis was not weighed. The anatomical nomenclature follows Baumel et al. (1993), and the abbreviations used in text are as follows: m. (muscle), mm. (muscles), and p. (pars). 179 VERTEBRATE ZOOLOGY — 68 (2) 2018 Table 1. Wing muscles, the mean muscular mass (g), standard deviation (SD) and percentage of body mass (%BM), in brackets, the average body mass. DW/UP: humeral muscles that acts during the downstroke and upstroke respectively (following Dial, 1992). Muscle function according to: 1 Raikow (1985), 2 Dial (1992), 3 Vazquez (1995). Muscle Main function Caracara plancus (1358.00 g) Milvago chimango (302.50g) Milvago chimachima ( 315.50g) Mean SD %BM Mean SD %BM Mean SD %BM M. latissimus dorsi cranialis retracts the humerus 10.83 0.27 0.06 0.10 0.04 0.03 0.22 0.13 0.07 M. latissimus dorsi caudalis 1.68 0.33 0.12 0.32 0.03 0.11 0.21 0.13 0.06 M. rhomboideus (superficialis + profundus) stabilization of the thoracic girdle 12.38 0.71 0.17 0.41 0.02 0.14 0.41 0.10 0.13 M. serratus superficialis cranialis stabilization of the thoracic girdle 1 0.37 0.09 0.03 0.09 0.04 0.03 0.05 0.01 0.02 M. serratus superficialis caudalis 1.10 0.38 0.08 0.22 0.07 0.07 0.21 0.06 0.06 M. serratus profundus 0.62 0.12 0.05 0.10 0.06 0.03 0.06 0.03 0.02 M. pectoralis p. thoracica retracts and depress the humerus/DW 271.97 10.73 5.27 15.99 2.00 5.28 15.26 0.79 4.84 M. deltoideus propatagialis p. cranialis tense the propatagium 22.59 1.41 0.19 0.38 0.10 0.12 0.36 0.01 0.11 M. deltoideus propatagialis p. caudalis tense the propatagium 2————————— M. supracoracoideus elevates humerus/UP 25.26 0.96 0.38 1.04 0.14 0.34 0.68 0.01 0.21 M. deltoideus p. major elevation of humerus and wings/UP 27.25 2.30 0.53 1.29 0.19 0.43 1.26 0.16 0.40 M. deltoideus p. minor Protracts and elevates the humerus 10.29 0.23 0.02 0.01 — 0.00 0.12 — 0.04 M. coracobrachialis cranialis protracts and depress the humerus 10.63 0.17 0.05 0.18 0.11 0.06 0.11 0.01 0.03 M. coracobrachialis caudalis depress and rotates the humerus/DW 12.59 1.37 0.19 0.38 0.09 0.13 0.29 0.06 0.09 M. scapulohumeralis caudalis retracts the humerus, rotation of the wing/DW 21.08 0.33 0.79 0.11 0.26 0.64 0.04 0.20 — M. scapulohumeralis cranialis retracts the humerus 10.01 0.00 0.02 0.01 0.01 — — — — M. subscapularis retracts the humerus/DW 2 2.31 0.75 0.17 0.53 0.03 0.18 0.41 0.04 0.13 M. subcoracoideus depress and rotates the humerus dorsally/DW 2 M. scapulotriceps stabilizes the elbow/UP 24.16 1.20 0.30 0.63 0.15 0.21 0.64 0.11 0.20 M. humerotriceps extends the elbow/DW 24.47 1.20 0.33 0.74 0.05 0.25 0.64 0.05 0.20 M. biceps brachii stabilizes the elbow, flex the forearm/DW 25.34 1.11 0.39 0.80 0.08 0.26 0.94 0.21 0.30 M. brachialis flex the elbow 10.49 0.15 0.04 0.08 0.02 0.03 0.08 — 0.03 M. pronator superficialis ventral rotation of the wing 20.97 0.27 0.07 0.15 0.03 0.05 0.12 0.00 0.04 M. pronator profundus ventral rotation of forearm 11.94 0.39 0.14 0.36 0.04 0.12 0.31 0.06 0.10 M. flexor digitorum superficialis flex the wrist and extend digiti majoris 30.66 0.15 0.05 0.14 0.04 0.05 0.11 0.04 0.03 M. flexor carpi ulnaris flex the wrist 22.25 0.72 0.17 0.49 0.07 0.16 0.43 0.09 0.13 M. flexor digitorum profundus flex the wrist 30.72 0.20 0.05 0.16 0.03 0.05 0.12 0.00 0.04 M. ulno-metacarpalis ventralis flex and pronates the wrist 30.58 0.12 0.04 0.12 0.01 0.04 0.12 0.04 0.04 M. supinator Rotates forearm 10.31 0.08 0.02 0.06 0.02 0.02 0.02 — 0.01 M. extensor carpi radialis extends the wrist 22.43 0.41 0.18 0.42 0.05 0.14 0.43 0.03 0.14 M. extensor digitorum communis wrist flexion and stabilization 30.69 0.13 0.05 0.14 0.02 0.04 0.11 0.01 0.03 M. extensor carpi ulnaris flex the wrist 30.77 0.23 0.06 0.14 0.02 0.05 0.11 0.02 0.03 M. ectepicondilo ulnaris elevates forearm 11.02 0.21 0.07 0.19 0.02 0.06 0.13 0.01 0.04 M. extensor longus alulae extends the wrist 30.83 0.31 0.06 0.15 0.02 0.05 0.13 0.01 0.04 M. extensor longus digiti majoris exteds digiti majoris 30.53 0.11 0.04 0.12 0.02 0.04 0.08 0.03 0.03 Picasso, M.B.J. & Mosto, M.C.: Wing myology of Caracaras (Aves, Falconiformes) 180 Results Muscular description The m. latissimus dorsi (Fig. 1A – D) has two independent portions: the p. cranialis and the p. caudalis. The p. cranialis (Fig. 1A – C) is a fleshy band-shaped muscle that originates on the spinous process of the cervical vertebrae and inserts into the medial facet of the corpus humeri, covering the second proximal quarter (Fig. 2A). The p. caudalis (Fig. 1A – D) is also a fleshy band-shaped muscle, although wider and thicker than the p. cranialis, which is situated on the m. rhomboideus superficialis. It inserts into the humerus via a tendon (Fig. 2A), which is common to that of the origin of the m. scapulotriceps. The m.rhomboideussuperficialis(Fig. 1A – D) is a fleshy muscle with two distinct and contiguous fleshy portions (cranial and caudal) that originate on the last cervical vertebrae. The cranial portion is square-shaped and inserts into the first quarter of the scapula (Fig. 2C), whereas the caudal portion is wider than the cranial one and inserts into the scapula, reaching the region of the angulus subterminalis (sensu liVezey & suzy, 2006; Fig. 2C). The m. rhomboideus profundus (Fig. 2D) is a fleshy muscle that originates on the cervical vertebrae and inserts into the medial surface of the scapula. It is located right beneath the m. rhomboideus superficialis, from which it is difficult to separate. The m.serratussuperficialis(Fig. 1A) consists of two independent bellies: the p. cranialis and the p. caudalis. The p. cranialis is a fleshy band-shaped muscle that originates on the ribs near the processus uncinatus, and attaches on the cranial half of the scapula between the two bellies of the m. subescapularis (Fig. 2D). The p. caudalis is a fleshy, broad and flat muscle that originates on the caudal ribs, covering the processus uncinatus, and inserts into the medial surface and ventral end of the scapula, on the last caudal third (Fig. 2C). The m. serratus profundus is a fleshy and flat muscle that originates on the first ribs and inserts into the medial surface at the third caudal quarter of the scapula (Fig. 2D). The m. pectoralis p. thoracica (Fig. 3A, C) is a fleshy well-developed muscle that originates on various structures: the carina sterni, the ventral aspect of the clavicula (Fig. 2B) and the membranes sternocoracoclavicularis and cristoclavicularis. The muscle inserts into the proximal region of the corpus humeri on the crista deltopectoralis (Fig. 2B). The m. pectoralis propatagialis p. longus (Fig. 4A, B) is a small, fleshy and elongated portion of the muscle pectoralis p. thoracica, with an elastic tendon that penetrates the propatagium and gives support to its leading edge. Table 1 continued. Muscle Main function Caracara plancus (1358.00 g) Milvago chimango (302.50g) Milvago chimachima ( 315.50g) Mean SD %BM Mean SD %BM Mean SD %BM M. ulnometacarpalis dorsalis flex the wrist 30.57 0.07 0.04 0.06 0.00 0.02 0.05 0.03 0.02 M. interosseous dorsalis elevates digiti majoris 30.19 0.03 0.01 0.04 — 0.01 0.04 — 0.01 M. interosseus ventralis flex digiti majorisb 30.17 0.03 0.01 0.05 0.02 0.02 0.03 — 0.01 M. extensor brevis alulae extends alular digit 30.06 0.05 0.01 — —- — -- — — M. abductor alulae extends and depress alular digit 30.09 0.02 0.01 — —- — — — — M. flexor alulae depress alular digit 30.07 0.06 0.01 -- — — — — — M. adductor alulae flex alular digit 30.22 0.08 0.02 — — — — — — M. abductor digiti majoris extends digiti majoris 30.14 0.11 0.01 — — — — — — M. flexor digiti minoris flex digiti majoris and menoris 30.08 0.02 0.01 — — — — — — Forelimb mass 130.62 —10.26 24.27 —- 7.68 — — — Upstroke muscles 16.67 —1.22 2.96 —- 0.98 — — — Downstroke muscles 87.76 —7.14 18.56 —- 6.73 — — — 181 VERTEBRATE ZOOLOGY — 68 (2) 2018 The tendon inserts into the thick aponeurosis that covers the carpometacarpus, on the region of the processus extensorius. The m. deltoideus propatagialis p.cranialis (Fig. 4A – B) is a well-developed muscle that originates fleshy on the dorsal aspect of the furcula (Fig. 3B). The belly gives rise to a tendon that penetrates the patagium and bifurcates into two tendons, both of which insert into the tendon of origin of the m. extensor metacarpi radialis. The m. deltoideus propatagialis p. caudalis (Fig. 4B) is a small fleshy cranial portion of the m. deltoideus propatagialis p. cranialis, from which it is separated by a thin tendinous raphe. The muscle has a short tendon that fuses to the elastic tendon of the m. pectoralis propatagialis p. longus. The m. supracoracoideus (Fig. 5A – B) is a well-developed muscle that lies deep to the m. pectoralis, with a fleshy origin on the cranial half of the sternum (Fig. 3A), along the coracoideum (Fig. 3E) and on the membrane sternoclavicularis. The muscle passes through the canalis triosseus and inserts into the proximal end of the humerus, on the tuberculum dorsale (Fig. 2A). The m. deltoideus p. major (Figs. 1A – B and 4A) has two bellies that join together and insert via a tendon along the crista deltopectoralis of the humerus (Fig. 2A). The p. cranialis originates fleshy on the fibrocartilage humeroscapsularis and adjacent ligaments. The p. caudalis is fleshy and originates on the scapula (Fig. 2D). The m. deltoideus p. minor (Fig. 1A, B) is a poorly developed muscle located on the tendon of insertion of the m. supracoracoideus. The m. coracobrachialis cranialis (Fig. 5B) is a short fleshy muscle that originates on the coracoideum, on the extremitas omalis coracoidei (Fig. 3E). The muscle crosses the joint and inserts into the extremitas proximalis humeri (Fig. 2B). The m. coracobrachialis caudalis (Fig. 5A – B) originates fleshy on the sternal region, proximal to the coracoideum and the adjacent sternum (Fig. 3A, E). This muscle inserts by a tendon on the tuberculum ventrale of the humerus (Fig. 2A). The m. scapulohumeralis cranialis (Fig. 1C – D) is a small fleshy muscle that originates on the dorsal surface of the scapula and inserts into the humerus near the foramen pneumaticum, dividing the m. humerotriceps into internal and external bellies. The m. scapulohumeralis caudalis (Figs. 1A and 5 A – B) Fig. 1. Image and schematic drawings of the superficial muscles of shoulder and proximal humerus of Caracara plancus (A) and (D), Milvago chimachima (B) and Milvago chimango (C). Abbreviations: (dpmj) M. deltoideus p. major, (dpmn) M. deltoideus p. minor, (ht) M. humerotriceps, (ldca) M. latissimus dorsi caudalis, (ldcr) M. latissimus dorsi cranialis, (rs) M. rhomboideus (superficialis + profundus), (st) M. scapulotriceps, (se) M. subscapularis, (shca) M. scapulohumeralis caudalis, (shcr) M. scapulohumeralis cranialis, (spc) M. supracoracoideus, (ssca) M. serratus superficialis caudalis. Scale bars: 1 cm. A C B D Picasso, M.B.J. & Mosto, M.C.: Wing myology of Caracaras (Aves, Falconiformes) 182 has a fleshy origin along the caudal half of the scapula. The insertion is via a tendon on the caudal aspect of the foramen pneumaticum of the humerus. The m. subescapularis (Figs. 1D and 5C) has two fleshy portions, the caput laterale and the caput mediale, with the m. serratus superficialis between them. The caput laterale originates on the dorsal surface of the scapula (Fig. 2C), whereas the caput mediale originates on the ventral surface (Fig. 2D). Both portions join and give rise to a common tendon that inserts into the tuberculum ventrale of the humerus along with the tendon of the m. subcoracoideus (Fig. 2A). The m. subcoracoideus (Fig. 5A – C) is a fleshy muscle located on the medial aspect of the coracoideum, originated on the medial surface of the corpus coracoidei (Fig. 3D). It inserts by a common tendon into with the m. subescapularis on the tuberculum ventrale of the humerus to (Fig. 2A). The m. scapulotriceps (Figs.1 A – B and 5A) originates from an aponeurosis on the scapula, immediately posterior to the joint with the coracoideum (Fig. 2C). The fleshy portion shares the aponeurosis with the m. latissimus dorsi p. caudalis. The muscle inserts into the ulna on the impressio m. scapulotricipitis via a tendon (Fig. 6A). The m. humerotriceps (Fig. 1D) originates fleshy on the fossa pneumotricipitalis and the corpus humeri (Fig. 2A). It inserts both fleshy and tendinous into the olecranon (Fig. 6A). The m. biceps brachii (Figs. 5B and 7A) has a strong and wide tendon originated on the extremitas omalis of the coracoideum (Fig. 3E) and on the crista bicipitalis of the humerus (Fig. 2B). The muscle continues fleshy along the corpus humeri until the tendon of insertion approaches the ulna and radius, and then splits into two tendons, one of which inserts into the proximal end of the ulna and the other into the radius (Fig. 6B). Fig. 2. Muscular maps showing the sites of origin (red) and insertion (blue) of humerus in (A) dorsal and (B) ventral aspect; scapula in dorsal (C) and ventral (D) aspect. Scale bars: 1cm. A C B D 183 VERTEBRATE ZOOLOGY — 68 (2) 2018 Fig. 3. Muscular maps showing the sites of origin in (A) the ventral aspect of the sternum, (B) and (C) cranial and caudal aspect respectively of the clavicula, (D) and (E) dorsal and ventral aspect respectively of the coracoideum. Scale bars: 1cm. Fig. 4. Image and schematic drawings of Caracara plancus showing (A) the superficial dorsal muscles of the arm and forearm, (B) detailed view showing the small M. deltoideus p. propatagialis p.cranialis. Abbreviations: (dpmj) M. deltoideus p. major, (ecr) M. extensor carpi radialis, (st) M. scapulotriceps, (dpca) M. deltoideus p. propatagialis p. caudalis, (dpcr) M. deltoideus propatagialis p. cranialis, (pppl) M. pectoralis propatagialis p. longus Scale bars: 1cm. A A B B C D E Picasso, M.B.J. & Mosto, M.C.: Wing myology of Caracaras (Aves, Falconiformes) 184 The m. brachialis (Fig. 7A) is a short and fleshy muscle that originates on the fossa brachialis of the distal humerus, (Fig. 2B) and inserts into the depressio m. brachialis of the ulna (Fig. 6B). The m.pronator superficialis (Figs. 5C and 7B) originates from a short and strong tendon on the distal humerus (Fig. 2B). It inserts both fleshy and tendinous into the proximal radius (Fig. 6B). In Caracara plancus, the muscle originates both aponeurotic and fleshy. The m. pronator profundus (Fig. 7B) has a tendinous origin on the epicondilus ventralis of the humerus (Fig. 2B). The insertion is fleshy along the proximal third of the corpus radii (Fig. 6B). In Caracara plancus, the insertion reaches half way on the corpus radii. Them.flexordigitorumsuperficialis (Fig. 7A) is a thin muscle that originates tendinous on the epicondylus ventralis of the humerus (Fig. 2B). The belly gives rise to a tendon that inserts into the proximal phalanx of the digiti Fig. 5. Image and schematic drawings showing the ventral and deep muscles of the (A) sternum, (B) proximal humerus, (C) scapula and coracoideu, (A, C) Caracara plancus; (B) Milvago chimango. Abbreviations: (bb) M. biceps brachii, (ccr) M. coracobrachialis cranialis, (cca) M. coracobrachialis caudalis, (ecr) M. extensor carpi radialis, (fcu) M. flexor carpi ulnaris, (ps) M. pronator superficialis, (sbc) M. subcoracoideus, (se) M. subscapularis, (shca) M. scapulohumeralis caudalis, (spc) M. supracoracoideus, (st) M. scapulotriceps. Scale bars: 1cm. Fig. 6. Muscular maps showing the sites of origin (red) and insertion (blue) of the forearm, (A) dorsal aspect, (B) ventral aspect. Scale bars: 1cm. A A B B C 185 VERTEBRATE ZOOLOGY — 68 (2) 2018 majoris (Fig. 8A). This tendon runs along the cranioventral edge of the carpometacarpus along with the tendon of the m. flexor digitorum profundus. Them.flexorcarpiulnaris(Figs. 5C and 7B) is a welldeveloped muscle with a tendinous origin on the epicondylus ventralis of the humeri (Fig. 2A). The fusiform belly gives rise to a tendon that inserts into the os carpal ulnare (Fig. 8A). In Caracara plancus, the tendon of origin is strong. Them.flexordigitorumprofundus(Fig. 7B) has a fusiform belly that originates fleshy on the first third of the ulna (Fig. 6B), and a small part that also originates on the m. brachialis (Fig. 6B). It inserts into the distal phalanx of the digiti majoris via a tendon that runs along the carpometacarpus, where it is ossified (Fig. 8A). The m. ulnometacarpalis ventralis (Fig. 7A) has a fleshy origin on the ventral side of the ulna (Fig. 6 B). It inserts into the dorsal aspect of the proximal carpometacarpus near the origin of m. extensor brevis alulae via a tendon (Fig. 8B). The m. supinator (Fig. 7A) is a short muscle with a tendinous origin on the epicondylus lateralis of the humerus (Fig. 2B), sharing a common origin with the m. extensor digiti communis and the m. extensor metacarpalis cubitalis. It inserts fleshy into the first quarter of the corpus radii (Fig. 6B).Them.extensorcarpiradialis(Figs. 4A, 5B, 7B, and 9A) is a fusiform muscle with both a fleshy and tendinous origin. It originates on the processus supracondylaris dorsalis of the distal humerus (Fig. 2B). It inserts tendinous into the processus extensorius of the carpometacarpus (Fig. 8A). The m.extensor digitorum communis (Fig. 9A) is a V-shaped muscle with an aponeurotic origin on the epicondilus dorsalis of the humerus (Fig. 2B). The belly is fusiform and the insertion is by a bifurcated tendon on two digits. The short tendon inserts into the phalanx of the digiti alulae (Fig. 8B), whereas the long tendon passes through the sulcus tendineus of the carpometacarpus and inserts into the base of the proximal phalanx of the digiti majoris (Fig. 8B). The next four muscles have a common origin on the epicondylus lateralis of the humerus (Fig. 2B). The m.extensor carpi ulnaris (Fig. 9A) originates on the surface of the m. ectepicondylo-ulnaris via a tendon (Fig. 2B). The belly is attached to the corpus ulnae (Fig. 6A) until the third quarter, where the tendon of insertion originates and finally inserts into the proximal carpometacarpus (Fig. 8B). The m. ectepicondylo-ulnaris (Fig. 9B) has a tendinous origin on the epicondylus lateralis of the humerus (Fig. 2B) and inserts fleshy into the ulna (Fig. 6A). Them.extensorlongusalulae(Fig. 9B) originates fleshy on the radius (Fig. 6B) and inserts into the processus extensorius of the carpometacarpus via a tendon (Fig. 8B). Them.extensorlongusdigitimajoris(Figs. 7A and 9A) has two portions: the p. proximalis and the p. distalis. Fig. 7. Image and schematic drawings of the ventral aspect of the forearm showing (A) superficial and (B) deep muscles in Caracara plancus. Abbreviations: (b) M. brachialis, (bb) M. biceps brachii, (ecr) M. extensor carpi radialis, (eldmpp) M. extensor longus digiti majoris, (fcu) M. flexor carpi ulnaris, (fds) M. flexor digitorum superficialis, (fdp) M. flexor digitorum profundus, (pp) M. pronator profundus, (ps) M. pronator superficialis, (s) M. supinator, (ud) M. ulnometacarpalis dorsalis, (uv) M. ulno-metacarpalis ventralis. Scale bars: 1cm. A B