Valecchi, Debora, Duccio Bacci, Massimo Gulisano, Eleonora Sgambati, Maurizio Sibilio, Mario Lipoma, and Claudio Macchi. 2010. “Internal Jugular Vein Valves: An Assessment of Prevalence, Morphology and Competence by Color Doppler Echography in 240 Healthy Subjects”. Italian Journal of Anatomy and Embryology 115 (3):185-89. https://oajournals.fupress.net/index.php/ijae/article/view/1079.