part of part of composed primarily of camera-type eye smooth muscle tissue eyelid muscle eye muscle orbitalis muscle Wikipedia:Orbitalis_muscle orbitalis orbital muscle NCIT:C52800 An orbitalis muscle is a rudimentary nonstriated muscle (smooth muscle) that crosses from the infraorbital groove and sphenomaxillary fissure and intimately united with the periosteum of the orbit. It is often called Muller's muscle. One characteristic of Horner's Syndrome is enophthalmos (retraction of the eyeball into the orbit due to paralysis of the orbitalis muscle that spans the inferior orbital fissure). Its function is eyeball protrusion. SCTID:368790005 FMA:49034 EMAPA:37691 subclass of 'muscle layer' in FMA orbital muscle of muller UBERON:0006318 UMLS:C0229105 orbitalis musculus orbitalis musculus orbitalis MA:0001274