Openings of pulmonary veins

The openings of the pulmonary veins are the sites where the pulmonary veins enter the left atrium, forming the venous ostia.

• In dogs, five or six openings of pulmonary veins (ostia venarum pulmonalium) are described into the left atrium. The two or three veins coming from the right lung cross dorsal to the right atrium and open into the craniodorsal part of the lef atrium; the three veins from the left lung usually empty into its caudodorsal part. The veins from the caudal lobes are most caudal in position and larger than the others pulomary veins.

• In humans, these ostia are typically four in number—right superior, right inferior, left superior, and left inferior pulmonary veins—although anatomical variants such as a common ostium or supernumerary veins are frequently observed.