Variations in the Basal Vein. D, An uncommon variation results when both the anterior and posterior basal anastomotic veins are rudimentary. In this case, a completely fragmented basal vein is encountered. The striate segment drains anteriorly through the preuncal vein, the peduncular segment drains inferiorly through the lateral mesencephalic vein, and the tributaries of the mesencephalic segment drain directly into the vein of Galen or internal cerebral vein. E, As in the previous case, both the anterior and posterior anastomotic veins are rudimentary, but a prominent anterior pontomesencephalic vein, and not a preuncal vein, drains the striate segment inferiorly. F, A combination of rudimentary posterior basal anastomotic vein and prominent preuncal vein characterizes this uncommon variation, where the anterior and posterior peduncular and striate segments drain anteriorly. (Images courtesy of AL Rhoton, Jr.)