All specimens studied are in The University of Kansas Museum of Natural History. They were preserved in alcohol and their blood vessels were not injected. Dissections were made with the aid of a binocular microscope at magnifications of 10x and 20x. Following is a list of the species studied, the number of individuals of each species dissected, and the catalogue numbers of the specimens. The nomenclature and classification are those of the American Ornithologists' Union's _Check-List of North American Birds_, fifth edition (1957). Family Columbidae _Zenaidura macroura_ (Linnaeus), Mourning Dove 2: 40325, 40326. _Zenaida asiatica_ (Linnaeus), White-winged Dove 1: 40328. _Scardafella inca_ (Lesson), Inca Dove 5: 34894, 34896, 34902, 34906, 34907. _Columba livia_ Gmelin, Rock Dove (domestic pigeon) 1: 40321. Family Hirundinidae _Iridoprocne bicolor_ (Vieillot), Tree Swallow 1: 38101. _Progne subis_ (Linnaeus), Purple Martin 5: 37711, 38794, 38796, 38798, 38804. _Stelgidopteryx ruficollis_ (Vieillot), Rough-winged Swallow 1: 38277. _Riparia riparia_ (Linnaeus), Bank Swallow 2: 38784, 38785. _Hirundo rustica_ (Linnaeus), Barn Swallow 1: 38839. The following descriptions are 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