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.