Dimples are visible inentations of the skin, caused by underlying flesh, which form on some people's cheeks when they smile. Dimples are genetically inherited and are a dominant trait. Dimples on each cheek are a relatively common occurrence for people with dimples. A rarer form is the single dimple, which occurs on one side of the face only. Anatomically, dimples may be caused by variations in the structure of the facial muscle known as zygomaticus major. Specifically, the presence of a double or bifid zygomaticus major muscle may explain the formation of cheek dimples. This bifid variation of the muscle originates as a single structure from the zygomatic bone. As it travels anteriorly, it then divides with a superior bundle that inserts in the typical position above the corner of the mouth. An inferior bundle inserts below the corner of the mouth.