The superficial brachial artery passing superficially to the pectoral ansa, the highest superficial brachial artery (Arteria brachialis superficialis suprema).

The human superficial brachial artery passes superficially to the median nerve and can be classified into three subtypes according to its topographical relationship to the pectoral ansa. When the superficial brachial artery passes superficially to the pectoral ansa, it is defined as the highest superficial artery. We found the highest superficial brachial arteries in both arms of a single cadaver. The right one coexisted with a normal axillary artery, and its identification was not difficult. The left one ran medially to the brachial plexus proximally and became superficial to the brachial plexus after branching off the artery, which gave the subscapular artery, then passed between the radial nerve and its accessory root from deep to superficial and ended as an inferior collateral ulnar artery. We also found a muscular axillary arch in each of the arms, both of which were innervated by the medialmost branch from the pectoral ansa. The right highest superficial brachial artery passed deep to the nerve to the muscular axillary arch. We conjectured that the left axillary artery is where the highest superficial brachial artery, as found on the right, coexists with the axillary artery in the case of Adachi's C-type brachial plexus (AxC). Then, the highest superficial brachial artery develops as a main stem, and the latter remains as a rudimentary AxC. Because the left axillary artery is caught on neither the pectoral ansa nor its branches, the left axillary artery can shift medially to the brachial plexus, and its true form is not obvious.