The orbicularis oris is a muscle that is located around the mouth and is is responsible for some mouth movements, particularly the ability to pucker the lips when the mouth is closed. The orbicularis oris is one of several sphincter muscles located in the human body. A sphincter muscle is generally shaped like a circle. It works by closing an opening or body passage. The human body contains many sphincter muscles, many of them being so small that they can not be seen with the naked eye.