Left Foramen of Monro with Transchoroidal Trajectory Demonstrated. The body of the fornix can be seen along image right with the choroid plexus visible immediately lateral to it. The columns of the fornix form the anterior and superior wall of the foramen of Monro. The choroidal fissure, located between the thalamus and fornix, is opened by dividing the tenia fornix that attaches the choroid plexus to the lateral edge of the fornix, leaving the attachment of the choroid plexus to the thalamus undisturbed. The tenia fornix, which attaches the choroid plexus to the fornix, has been divided. The medial posterior choroidal artery is visible following dissection. (Image courtesy of AL Rhoton, Jr.)