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.

SUMMARY OF ARTERIAL ARRANGEMENT

In both families the vessels that are relatively constant in appearance
are: a subclavian giving rise to the carotid and axillary arteries, and
becoming the pectoral trunk; the thoracic artery arising variously, and
passing posteriorly to the rib cage; and the coracoid complex of
vessels. The coracoid complex includes the coracoid artery, the vessels
to _Mm. sternocoracoideus_ and _coracobrachialis posterior_, and the
sternal artery, which is variously present, and more extensive in some
species than in others.

DISCUSSION AND CONCLUSIONS

In the vessels studied individual variation is marked, but the arterial
ar