Anterior view of midbrain.  The crus cerebri is the anterior portion of the cerebral peduncle that contains descending motor fibers of the frontopontine tract and corticospinal tract.  The interpeduncular fossa is a midline depression located between the cerebral peduncles and limited anteriorly by the optic chiasm.  The oculomotor nerve (CN III) emerges from the interpeduncular fossa. The posterior perforated substance is an area of grey matter located in the interpeduncular fossa that derives its name from the appearance of many small apertures that transmit branches of the posterior cerebral arteries.  The mammillary bodies are part of the hypothalamus.  The infundibulum, or pituitary stalk, is the connection between the hypothalamus and the pituitary gland, which has been removed in this image. (Image courtesy of AL Rhoton, Jr.)