MYOLOGY AND ANGIOLOGY: COLUMBIDAE

Figs. 5, 6, and 7 illustrate the following muscles and arteries described for Scardafella inca.

Myology

M. pectoralis thoracica, Fig. 5. The origin is from approximately the ventral third of the keel, the lateral and anterior portion of the clavicle and the adjacent sterno-coraco-clavicular membrane, and from the lateral portion of the sternum and the fascia overlying the thoracic ribs. This massive muscle covers the entire ventral surface of the thorax, converges, and inserts on the pectoral surface on the ventral side of the humerus.

M. supracoracoideus, Fig. 5. The origin is from the dorsal two-thirds of the keel and medial half of the sternum (where the origin is bordered ventrally, posteriorly, and laterally by the origin of M. pectoralis thoracica) and from the sterno-coraco-clavicular membrane adjacent to the coracoid. This large pinnate muscle converges, passes through the foramen triosseum, and inserts by means of a strong tendon on the dorsal surface of the humerus on the deltoid ridge.

M. coracobrachialis posterior, Fig. 5. The origin is from a prominent lateral wing on the posterolateral portion of the coracoid, and from the lateral surface of the proximal two-thirds of the coracoid. The insertion is by means of a tendon on the internal tuberosity of the humerus. Of the muscles described here, this one differs most strikingly from the homologous muscle in P. subis. The difference can be seen by comparing Figs. 1 and 5.

M. sternocoracoideus, Figs. 5, 6, and 7. The origin is from the external, and to a slight extent from the internal, surface of the costal process. The insertion is on a posterolateral triangular area on the dorsal surface of the coracoid.

M. costi-sternalis, Figs. 5 and 6. The origin is from the anterior edge of the sternal portion of the first three thoracic ribs. The muscle converges and inserts on the apex of the costal process.

M. subcoracoideus (ventral head), Fig. 6. The origin is from the manubrium and from approximately the posterior half of the coracoid and on the medial and dorsal surface of that bone, and the medial side of the sterno-coraco-clavicular membrane adjacent to the coracoid. The ventral head passes anterodorsally to join with the dorsal head (not here described), and the combined muscle inserts by a tendon on the internal tuberosity of the humerus.

Mm. intercostales externus, Fig. 5. These muscles extend posteroventrally between successive thoracic ribs and between the last cervical and first thoracic ribs.

Mm. intercostales internus, Fig. 7. These muscles extend anteroventrally between the last three thoracic ribs.

Costopulmonary muscles, Fig. 7. This series of muscle slips from the thoracic ribs attaches to the aponeurosis covering the lungs.

Angiology

Figs. 5, 6, and 7 show all arteries discussed for this family. The numbers following names or descriptions of arteries in the text refer to numbered arteries in one of these figures. Insofar as possible, the numbers used for these arteries are the same numbers used for the homologous vessels in swallows.

The right and left innominate arteries arise from the aortic trunk and give rise to the common carotid (14) and subclavian (1) arteries. The latter continues across the thoracic cavity, giving rise to the coracoid (2) and axillary (10) arteries, and becoming the pectoral trunk. That trunk swings posteriorly and leaves the thoracic cavity near the apex of the costal process, as shown in Fig. 7. Where the trunk passes under M. sternocoracoideus, the thoracic artery (3) is given off.

The various branches of the coracoid artery, again referred to as a "coracoid complex," are as follows: The first branch, from the posterior face of the coracoid artery, is a relatively large vessel (6) here termed the sternal artery; it passes mediad across M. sternocoracoideus, sending off a branch (6a) to that muscle. The right sternal artery continues posteriorly on the mid-line of the inner surface of the sternum, and appears to send branches into the various pneumatic foramina of the sternum, but these vessels are minute and exceedingly difficult to trace accurately. The corresponding left vessel is smaller and ramifies on the anteromedial surface of the sternum. Variations found in these vessels were the following: In one specimen of S. inca the sternal artery had, on both sides, an independent origin from the subclavian, lateral to the origin of the coracoid artery. In Zenaidura macroura both right and left sternal arteries were similar to the left vessel described above, no median longitudinal vessel being seen. In Columba livia no vessel corresponding to the sternal artery was seen. In Zenaida asiatica these arteries penetrated M. sternocoracoideus; no branch to the sternum was seen.

A small complex of vessels (4 and 4a) arises from the lateral face of the coracoid artery and feeds M. coracobrachialis posterior, and occasionally M. sternocoracoideus. One branch (4a) passes under the coracoid and travels along the lateral side of that bone, supplying small branches to M. coracobrachialis posterior, and finally ramifying on the head of the coracoid. In C. livia, Zenaidura macroura, and Zenaida asiatica this complex usually arises independently from the subclavian, and in one case it arose from the axillary artery.

Two other branches from the coracoid artery were regularly seen. The first (8) passes across M. sternocoracoideus and appears to supply the area of the coracoid articulation with the sternum; the second (7) supplies M. subcoracoideus as the main vessel passes between that muscle and the coracoid and penetrates M. suparacoracoideus. A small notch on the medial side of the coracoid (shown in Figs. 6 and 7) often marks the passage of the coracoid artery.

All vessels of the coracoid complex are exceedingly variable, in number, size, and site of origin.

A prominent vessel (15) is given off from the posterior pectoral artery, outside the thoracic cavity, passes ventrad, and sends two branches into M. supracoracoideus. No corresponding artery was seen in the swallows dissected.

The thoracic artery (3), arising from the pectoral stem, characteristically bifurcates at the anterior end of M. costi-sternalis. The dorsal, and larger, branch passes posteriorly, sends several small branches to M. costi-sternalis, and continues to the most posterior rib. The ventral trunk bifurcates, one branch passing along the edge of, and supplying, M. costi-sternalis, the other branch passing onto the surface of the sternum. In some specimens two such branches to the sternum were seen.