Openings of pulmonary veins
Ostia venarum pulmonalium
Definition
The pulmonary veins, four in number, open into the upper part of the posterior surface of the left atrium—two on either side of its middle line: they are not provided with valves. The two left veins frequently end by a common opening.
References
This definition incorporates text from a public domain edition of Gray's Anatomy (20th U.S. edition of Gray's Anatomy of the Human Body, published in 1918 – from http://www.bartleby.com/107/).