The diaphragma sellae or sellar diaphragm is a flat piece of dura mater with a circular hole allowing the vertical passage of the pituitary stalk. It retains the pituitary gland beneath it in the fossa hypophyseos as it almost completely roofs the fossa hypophyseos of the sella turcica, a part of the sphenoid bone. It has a posterior boundary at the dorsum sellae and an anterior boundary at the tuberculum sellae along with the two small eminences (one on either side) called the middle clinoid processes. The diaphragma sellae is innervated by the first division of the cranial trigeminal nerve.