part_of part of is part of part of develops from has muscle origin has muscle insertion has muscle antagonist anatomical structure connected anatomical structure system muscle of iris sphincter pupillae http://upload.wikimedia.org/wikipedia/commons/2/2f/Gray878.png constricts iris spincter pupillae circular fibers pupillary constrictor muscle sphincter pupillae muscle EMAPA:35788 FMA:49157 WP says: It is found in vertebrates and some cephalopods; this class refers to the vertebrate structure BTO:0000656 iris constrictor muscle UBERON:0001607 m. sphincter pupillae pupillary sphincter muscle musculus sphincter pupillae pupillary sphincter iris sphincter UMLS:C0229189 uberon M. sphincter pupillae sphincter pupillae NCIT:C33586 iris constrictor constrictor pupillae In humans, it functions to constrict the pupil in bright light or during accommodation. Its dimensions are about 0.75 mm wide by 0.15 mm thick. It is controlled by parasympathetic fibers that originate from the Edinger-Westphal nucleus, travel along the oculomotor nerve (CN III), synapse in the ciliary ganglion, and then enter the eye via the short ciliary nerves. Initially, all the myocytes are of the smooth muscle type, but much later in life, so that ultimately most cells are of the striated muscle type. [WP,unvetted] sphincter muscle of pupil MA:0001289 A sphincter muscle that is part of the iris. iris sphincter muscle dilatator pupillae iris neurectoderm iris smooth muscle sphincter muscle smooth muscle sphincter