The New International Encyclopædia/Perinæum

PERINÆUM (Neo-Lat., from Lat. perinæon, perineon, from Gk. περίναιον, perinaion, περίνεον, perineon, περινός, perinos, perinæum). The part of the human body which forms the floor of the true pelvis is by anatomists divided into two portions. Of these, the anterior one, situated in front of the anus, is called the true perinæum, or urethral (or, in the female, the vaginal) portion of the perinæum; the posterior portion, which contains the anus or termination of the rectum, is called the rectal or anal portion of the perinæum. The anterior portion, or true perinæum, is triangular in form, the apex being in front; the sides, about three inches in length, are formed by the rami of the pubes and ischium, and the base by an imaginary line joining the tuberosities of the ischium, and passing about half an inch in front of the anus. Through this space the urethra passes through a layer of strong fascia—the deep perinæal fascia—to communicate with the bladder, and in this space the opening is made in the operation of lithotomy.

In the female the space usually referred to as the perinæum lies between the vagina in front and the anal orifice behind. Its most important constituent is the anterior portion of the levator ani muscle. The perinæum, including a greater or less extent of this muscle and sometimes also the sphincter ani muscle, is often torn during parturition, and requires suturing for its repair.