Galen’s circulatory paradigm and early illustrations of the DA. (A) Galen’s scheme described transmission of blood across inter-ventricular pores to spread vital spirit in the body. (Adapted with permission from Dr. Barbara J. Becker, UC Irvine, and the Wellcome Collection (licensed under Creative Commons 4.0, CC BY).) (B) Hieronymus Fabricius of Aquapendente’s drawing shows the DA (“E”) as a prominent extension of the main pulmonary artery (“F”), similar in caliber to the ascending aorta (“D”), which was described as “the offshoot of the great artery to the artery-like vein, … a wide vessel in the fetus but becomes cord-like after birth.” (De formato fetu, 1600 AD). (Adapted with permission from Refs.,) (C) Johan van Horne’s addendum to illustrations in Leonardo Bottalo’s Opera Omnia (1660 AD) depicted the DA (canalis a pulmonali arteria tendens in aortam) in an unusual orientation. (Adapted with permission from Ref).