The Musculus Sphincter Ani externus is a critical muscle in the human body responsible for controlling the opening and closing of the anal opening. This vital muscle has a few synonyms such as external anal sphincter, anus muscle, and anal sphincter external muscle. These synonyms are often used interchangeably in medical discussions and research papers. The external anal sphincter is a robust and powerful muscle that plays a vital role in the proper functioning of the digestive and elimination systems. Without it, we would not be able to control our bowel movements, leading to a lot of discomfort and inconvenience in our daily lives.