of _Progne subis_ and _Scardafella inca_.
Differences in the vascular system in other members of the families
represented by _P. subis_ and _S. inca_ are mentioned at the appropriate
places. The muscles briefly described for each of these two species are
those that are supplied by the thoracic or coracoid arteries or by
branches of the same, and muscles that, by their origin, location, or
insertion, seem to affect the course or origin of one of these arteries.

The following sources have been particularly useful for the terminology
of muscles and of skeletal features: Ashley (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