ABSTRACT
Three great venous systems appear successively during the embryonic period: cardinal, subcardinal and supracardinal. Four major transverse anastomoses occur, linking the three embryonic venous systems. The adult venous pattern emerges out of a shifting maze of reconstruction. The process is of interest, not only because it explains certain anatomical peculiarities of the thoracic and abdominal veins; it is of practical impor tance to the radiologist carrying out intravenous catheterization, on account of the frequent variations to which these veins are subject.
