Vel Azigos, (from α, neg. and a pair; without a fellow). The musculus azygos of Morgagni rises tendinous from the junction of the ossa palati, and runs down the palatum molle to the middle of the uvula, serving to elevate it.

A zygos processus. See Sphaenoides os.

A zygos vena. Vena sine pari. A vein situated within the thorax on the right side, having no fellow on the left. It arises posteriorly from the vena cava superior, a little above the pericardium; it is immediately bent backwards over the origin of the right lobe of the lungs, forming an arch which surrounds the great pulmonary vessels on that side, as the arch of the aorta does on those on the left, with this difference, that the curve of the azygos is directly backwards, but the other is oblique: from thence it runs down by the right side of the vertebrae dorsi, and before the intercostal arteries; and passing behind or below the diaphragm, it terminates by an anastomosis, sometimes with the vena renalis, at others with the neighbouring lumbar vein, sometimes immediately with the trunk of the vena cava inferior.

The vena azygos sends out branches from its upper part to the aspera arteria and bronchiae by the name of venas bronchiales; afterwards it sends out the inter-costales dextrae superiores; lower down, the intercosta-les dextrae inferiores.

Sometimes there is an azygos on the left side, proceeding from the arch of the common azygos: it is afterwards distributed in the same manner as the other on the right side; but this disposition is very variable.

The azygos having reached the last rib, sends off a large branch, which, bending outwards, perforates the muscles of the belly, is ramified betwixt different planes, and communicates with the branches of the intercostal veins which run there.