(1941), Beddard (1898), Coues (1903), Howard (1929), Howell (1937), and Hudson and Lanzillotti (1955).

The names used for most arteries are those in common usage for vertebrates. I have not used the terms "internal mammary" and "intercostal" artery as substitutes for "thoracic" artery, except when referring to the work of others. The vessel's homology with the internal mammary artery of mammals has been denied (Glenny, 1955:541), and the name "mammary" is certainly not useful descriptively in birds. The term "intercostal" is less objectionable, except that such a name may call to mind segmental vessels arising from the dorsal aorta. The term "thoracic" seems best, as it is reasonably descriptive, and has been used by Glenny in the majority of his descriptions covering a wide variety of birds. The name "sternoclavicular" has been used by others as a synonym for the "coracoid" artery. I have arbitrarily chosen to use the latter.

ACKNOWLEDGMENTS

I gratefully acknowledge many valuable suggestions in my research and the preparation of this manuscript from Professors Theodore H. Eaton, A. Byron Leonard, Richard F. Johnston, Robert M. Mengel, and E. Raymond Hall. Mr. Abbot S. Gaunt and Miss Sandra Lovett assisted in collecting specimens. Final drafts of the illustrations were prepared by Mr. Thomas Swearingen.

MYOLOGY AND ANGIOLOGY: HIRUNDINIDAE

Figs. 1, 2, 3, and 4 illustrate the following muscles and arteries described for Progne subis.

Myology

M. pectoralis thoracica, Fig. 1. The origin is from slightly less than the posterior half of the sternum, from the ventral half of the keel, almost the entire length of the posterolateral surface of the clavicle and adjacent portion of the sterno-coraco-clavicular membrane, and tendinously from the ventral thoracic ribs. This massive muscle covers the entire ventral surface of the thorax and converges to insert on the ventral side of the humerus on the pectoral surface.

M. supracoracoideus, Fig. 1. The origin is from the dorsal portion of the keel and medial portion of the sternum, and is bordered ventrally by the origin of M. pectoralis thoracica, and laterally by M. coracobrachialis posterior. The origin is also from the manubrium and the anterolateral portion of the proximal half of the coracoid and to a slight extent from the sterno-coraco-clavicular membrane adjacent to the manubrium. This large pinnate muscle converges, passes through the foramen triosseum, and inserts by a tendon on the external tuberosity of the humerus, immediately proximal to the insertion of M. pectoralis thoracica.

M. coracobrachialis posterior, Figs. 1 and 3. The origin is from the dorsolateral half of the coracoid, anterolateral portion of the sternum (where the area of origin is bordered medially by M. supracoracoideus, posteriorly by M. pectoralis thoracica, and laterally by M. sternocoracoideus), and also to a slight extent from the area of attachment of the thoracic ribs to the sternum. The muscle fibers converge along the lateral edge of the coracoid and insert on the median crest of the humerus immediately proximal to the pneumatic foramen. In passing from the origin on the sternum to the insertion on the humerus, the belly of the muscle bridges the angle formed by the costal process of the sternum and the coracoid.

M. sternocoracoideus, Figs. 2 and 3. The origin is from the entire external surface of the costal process of the sternum, and to a small extent from the extreme proximal ends of the thoracic ribs where they articulate with the costal process. The muscle inserts on a triangular area on the dorsomedial surface of the coracoid. Like M. coracobrachialis posterior, this muscle bridges the angle formed by the costal process and the coracoid.

M. subcoracoideus (ventral head), Figs. 2 and 3. The origin is from the dorsomedial edge of the coracoid at its extreme proximal end, and to a slight extent from the adjacent portion of the manubrium. The origin is medial to the insertion of M. sternocoracoideus. The ventral head passes anterodorsally along the medial edge of the coracoid and joins the dorsal head (not here described). The combined muscle then inserts by a tendon onto the internal tuberosity of the humerus.

M. costi-sternalis, Figs. 1, 2, and 3. The origin is from the anterior edge of the sternal portion of the first four thoracic ribs. This triangular muscle narrows and inserts on the posterior edge of the apex of the costal process. The portion arising from the first rib may share slips with M. sternocoracoideus.

M. costi-sternalis anterior, Figs. 1, 2, and 3. This muscle is variously developed, and originates from a small area on the ventral end of the vertebral portion of the last cervical rib. The insertion is on the apex of the costal process, immediately anterior to the insertion of M. costi-sternalis.

Mm. intercostales externus, Fig. 1. These muscles extend posteroventrally between the vertebral portions of successive thoracic ribs, and between the last cervical and first thoracic ribs. In the more posterior intercostal spaces these muscles are poorly developed, but they become progressively better developed anteriorly, and are fully represented in the most anterior intercostal spaces.

Mm. intercostales internus, Fig. 3. These muscles resemble the external intercostal muscles, but extend anteroventrally, with the muscles being most fully developed posteriorly, and progressively less so anteriorly.

Costopulmonary muscles, Fig. 3. This diagonal series of muscle slips from the thoracic ribs attaches to the aponeurosis covering the lungs.

Angiology

Figs. 3 and 4 show all arteries discussed for this family. The numbers following the names or descriptions of arteries in the text refer to numbered arteries in one or both of these figures.

The right and left innominate or brachiocephalic arteries arise from the aortic trunk and give rise to the common carotid arteries (14). The major vessel continuing across the thoracic cavity is the subclavian artery. Classically the subclavian is considered as continuing into the anterior appendage as the axillary artery. However, in the species studied, the axillary artery can best be described as a branch from the subclavian; the pectoral stem forms a more direct continuation of the subclavian. In traversing the thoracic cavity, the subclavian gives rise to the thoracic, coracoid, and axillary arteries, and leaves the thoracic cavity as the pectoral trunk, dorsal to the area where Mm. coracobrachialis posterior and sternocoracoideus span the angle formed by the coracoid and costal process.

The pectoral trunk bifurcates into two main pectoral arteries (9), which penetrate M. pectoralis thoracica. Neither the axillary artery nor these pectoral arteries were traced in my study.

The coracoid artery (2) arises from the ventral face of the subclavian (1), either opposite the base of, or medial to, the axillary artery (10). The coracoid artery passes ventrad between the medial edge of the coracoid and the ventral head of M. subcoracoideus, and an artery (7) is given off to supply that muscle. The main vessel then penetrates M. supracoracoideus and bifurcates or ramifies into several vessels (12).

Between the origin of the coracoid artery from the subclavian, and the point where the coracoid artery passes the medial edge of the coracoid, several branches are given off. These vessels are highly variable in origin, as described below, and not all were always found. Along with the coracoid artery, they are termed a