Anatomy. The external anal sphincter measures about 8 to 10 cm in length, from its anterior to its posterior extremity, and is about.
Anatomical terms of muscle. [edit on Wikidata]. The internal anal sphincter, IAS, ( or sphincter ani internus) is a ring of smooth muscle that.
The external sphincter is a layer of voluntary (striated) muscle encircling the outside wall of the anal canal and anal opening. A second sphincter, the external anal sphincter, is composed of striated muscle and is divided into three parts known as the subcutaneous, superficial.