But up above all these,

from that part which is connected with the
heart, the entire vein branches off in two directions. For its
branches extend to the sides and to the collarbones, and then pass on,
in men through the armpits to the arms, in quadrupeds to the forelegs,
in birds to the wings, and in fishes to the upper or pectoral fins.
(See diagram.) The trunks of these veins, where they first branch
off, are called the 'jugular' veins; and, where they branch off to
the neck the great vein run alongside the windpipe; and,
occasionally, if these veins are pressed externally, men, though not
actually choked, become insensible, shut their eyes, and fall flat on
the ground. Extending in the way described and keeping the windpipe
in betwixt them, they pass on until they reach the ears at the
junction of the lower jaw with the skull.