It borders another muscle known as the Sphincter Ani Externus. Together these muscles seal the anal cavity and expel fecal matter. They play an important role in bowel continence. When the Sphincter Ani Externus is not working correctly, it may cause liquid fecal incontinence or mucous rectal discharge. Damage to the Sphincter Ani Externus may occur during childbirth or anal and rectal surgery. These muscles can also become weak with age.
The Sphincter Ani Internus is often called the Internal Anal Sphincter. This is also known by the acronym IAS.