Anterior view of the pituitary gland and surrounding structures. For orientation, superior is toward the bottom of the image. Large portions of the frontal and sphenoid bones have been removed. The pituitary gland and stalk can be seen in the center of the image. The optic chiasm is located superior and anterior to the pituitary gland and the optic nerves are visible as they emerge from the optic canals. The cavernous segments of the internal carotid arteries (ICA) can be seen on either side of the pituitary gland coursing within the cavernous sinus.  The superior hypophyseal artery arises from the ICA. Lateral to the optic chiasm the ICA divides into its terminal branches: the anterior and middle cerebral arteries. The middle cerebral artery (MCA) courses laterally, while the anterior cerebral artery (ACA) courses medially and anteriorly. The A1 segment of the ACA is between the internal carotid bifurcation and the anterior communicating artery, which connects the two ACAs across the midline. The A2 (infracallosal) segment of the ACA continues anteriorly and is inferior to the rostrum of the corpus callosum. The recurrent artery of Heubner can be seen arising from the A2 segment of the ACA. The clivus has also been resected to show the pons and the overlying basilar artery with the anterior inferior cerebellar artery arising from it. (Image courtesy of AL Rhoton, Jr.)