surface of the sternum, and often a
large branch continues across the dorsal surface of the coracoid to _M.
coracobrachialis posterior_. Fig. 3 shows a composite of these vessels;
not all branches were seen in any one specimen. In the specimen of _I.
bicolor_ a foramen existed on the lateral edge of the coracoid where the
branch (of 8) to _M. coracobrachialis posterior_ passed. An examination
of skeletons of five to 10 individuals each of the five species for
which dissections were made, and of _Petrochelidon pyrrhonota_ (Cliff
Swallow) and _Tachycineta thalassina_ (Violet-green Swallow), in the
University of Kansas collection, showed that most coracoids of these
seven species of swallows had a small notch (as shown in Fig. 4) or a
complete foramen there.

The thoracic artery (3) arises from the subclavian opposite the base of
the coracoid artery, or from the base of the coracoid artery. Of the
five specimens of _P. subis_ dissected, one individual had the former
arrangement on both sides, and one had the latter on both sides, whereas
in the remaining three the thoracic artery arose from the coracoid
artery on one side and from the subclavian on the other side. The
distance between these two possible sites of origin is slight.

The thoracic artery usually passes ventral to _M. costi-sternalis
anterior_. Occasionally a small artery (13) could be traced from the
main trunk of the thoracic artery to that muscle. The main thoracic
artery bifurcates near the insertion of _M. costi-sternalis_, the
branches traveling posteriad on both sides of the muscle. On one side of
one specimen this artery bifurcated immediately after leaving the
subclavian, the dorsal trunk passing dorsal to _M. costi-sternalis
anterior_, and the ventral trunk ventral to the muscle. On the other
side of the same individual the artery passed dorsal to _M.
costi-sternalis anterior_, bifurcating at the normal point.

From the ventral trunk of the thoracic artery a variable number of small
vessels arises to supply the costosternal articulations. The main
ventral trunk bifurcates into two branches, one of which passes onto the
inner face of the sternum, and one of which supplies the posterior two
intercostal spaces.

The dorsal thoracic trunk supplies _M. costi-sternalis_, several dorsal
intercostal areas, and the costopulmonary muscles. Minor variations in
all of the smaller branches of the thoracic artery were common.

MYOLOGY AND ANGIOLOGY: COLU