W, Superior view. The choroid plexus in the right lateral ventricle has been removed after opening the choroidal fissure from the foramen of Monro to the inferior choroidal point located just behind the head of the hippocampus. The axial section through the right hemisphere extends through the internal capsule. The genu of the internal capsule comes directly to the ventricular surface in the area lateral to the foramen of Monro. The lateral part of the floor of the temporal horn is formed by the collateral eminence, and the floor of the atrium is formed by the collateral triangle. Both the collateral eminence and trigone overlie the deep end of the collateral sulcus, which courses along the basal surface of the hemisphere between the parahippocampal and occipitotemporal gyri. The calcar avis, overlying the deep end of the calcarine sulcus, and the bulb, overlying the forceps major, are exposed in the medial wall of the atrium. X, Superior view of the temporal and occipital horns with the upper part of the hemisphere removed. The section extends through the depths of the calcarine sulcus. The cuneus, forming the upper lip of the calcarine sulcus, has been removed to expose the lingula, forming the lower lip of the fissure. The calcarine sulcus extends so deeply into the medial part of the hemisphere that it produces a prominence, the calcar avis, in the medial wall of the atrium and occipital horn. Y, Inferior view of the calcar avis. The lingula, forming the lower lip of the calcarine sulcus, has been removed to expose the cuneus, forming the upper lip of the sulcus. The calcarine sulcus cuts so deeply into the hemisphere that it produces a prominence in the medial wall of the atrium. The lateral atrial veins cross the lateral atrial wall. The lower part of the temporal lobe has been removed to expose the roof of the temporal lobe. The choroid plexus is attached to the lower surface of the thalamus. The anterior and lateral posterior choroidal arteries course along the medial edge of the choroid plexus. The anterior calcarine vein drains the depths of the calcarine sulcus. (Images courtesy of AL Rhoton, Jr.)