The =brachial vein= (V. brachialis) is a satellite of the extrathoracic
part of the brachial artery. It arises at the inner side of the distal
end of the shaft of the humerus and passes upward in the arm behind the
artery under cover of a layer of fascia and the posterior superficial
pectoral muscle. At the shoulder it is ventral to the artery, crosses
the anterior border of the first rib, and concurs with its fellow and
the two jugulars in the formation of the anterior vena cava. The roots
of the vein are somewhat variable, but most often four radial veins in
addition to a large oblique branch from the cephalic unite in its
formation. Its tributaries correspond in general to the branches of the
artery, but a few differences are worthy of notice. The
=thoracico-dorsal vein= joins the brachial directly or opens into the
deep brachial. The =external thoracic= or =“spur” vein= (V. thoracica
externa) is a large vessel which arises in the ventral wall of the
abdomen, passes forward (embedded more or less in the panniculus) along
the outer border of the posterior deep pectoral muscle, and joins the
brachial vein near the first rib. It often communicates with the
subscapular vein.
[Illustration: