Orbital muscle of Müller: observations on human fetuses measuring 35-150 mm.

The arrangement and relationships of the orbital muscle of Müller in human fetuses have been analyzed. This is a constant muscle made of smooth muscle fibers arranged over the longer axis of the inferior orbital fissure; some of its fibers reach the inferior wall of the cavernous sinus. The muscle layer is pierced by orbital rami of the medial maxillary artery and by thin veins communicating with the ophthalmic vein system and pterygoid plexus. The zygomatic nerve can be found in the midst of the muscle mass along most of its course. It is innervated by short rami from the sphenopalatine ganglion.