Left Lateral Ventricle with Retracted Fornix. The left fornix and interventricular septum (septum pellucidum) have been retracted medially to demonstrate the floor of the left lateral ventricle and the foramen of Monro.  The internal cerebral veins are visible bilaterally and receive drainage from the thalamostriate and anterior septal veins. The thalamostriate vein lies in the groove between the caudate and thalamus.  Portions of the medial posterior choroidal artery, which perfuses the choroid plexus within the roof of the third ventricle, are seen. (Image courtesy of AL Rhoton, Jr.)