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.
Figs. 5, 6, and 7 illustrate the following muscles and arteries described for _Scardafella inca_.
~_M. pectoralis thoracica~_, Fig. 5. The origin is from approximately the ventral third of the keel, the lateral and anterior portion of the clavicle and the adjacent sterno-coraco-clavicular membrane, and from the lateral portion of the sternum and the fascia overlying the thoracic ribs. This massive muscle covers the entire ventral surface of the thorax, converges, and inserts on the pectoral surface on the ventral side of the humerus.
~_M. supracoracoideus~_, Fig. 5. The origin is from the dorsal two-thirds of the keel and medial half of the sternum (where the origin is bordered ventrally, posteriorly, and laterally by the origin of _M. pectoralis thoracica_) and from the sterno-coraco-clavicular membrane adjacent to the coracoid. This large pinnate muscle converges, passes through the foramen triosseum, and inserts by means of a strong tendon on the dorsal surface of the humerus on the deltoid ridge.