Zygomatic major originates in the cheek bone (zygomatic arch) and inserts in muscles (o. oris, depressor, etc.) near the corner of the mouth. This muscle lifts the corner of the mouth obliquely upwards and laterally and is a muscle that produces a characteristic "smiling expression." (Other muscles produce different "smiles.") Some research suggests that the difference between a genuine smile and a perfunctory (or lying) smile is that when a person really feels happy, Zygomatic major contracts together with orbicularis oculi. Look at the videos below and see what you think (both expressions here are deliberate).

Zygomatic major is innervated by zygomatic and buccal branches of the facial nerve (VII) and is supplied with blood by the facial artery.