. . .y two sphincter muscles, the external being immediately beneath the skin surrounding the margin of the anus. It is elliptical in form, about half an inch in breadth on each side of the anus, and is attached posteriorly by a small tendon to the tip and back of the coccyx; anteriorly it becomes blended with the transverse and bulbo-cavernosus muscles at the central point of the perineum. The internal sphincter consists of the normal circular fibers of the rectum, considerably increased in number; its thickness is about two lines, and its vertical measurement from half an inch to an inch. It is situated immediately above and partly within the deeper portion of the external sphincter, being separated from it by a layer of fatty connective tissue.

These muscles—the two sphincters—are separated on the outer side by the attachment of the levator ani, some of the fibers of which are internally connected with the external sphincter; on the in. . . Read More