Perineum

[per-uh-nee-uhm]

In human anatomy, the perineum is generally defined as the surface region in both males and females between the pubic symphysis and the coccyx. The perineum is the region of the body inferior to the pelvic diaphragm and between the legs.

A diamond-shaped area on the inferior surface of the trunk which includes the anus and, in females, the vagina. Its definition varies: it can refer to only the superficial structures in this region, or it can be used to include both superficial and deep structures.

The perineum corresponds to the outlet of the pelvis.

The anogenital distance is a measure of male feminisation measuring the distance between the anus and the base of the penis. Studies show that the perineum is twice as long in males as in females. Measuring the anogenital distance in neonatal humans has been suggested as a noninvasive method to predict neonatal and adult reproductive disorders.

Boundaries

Its deep boundaries are as follows:

in front: the pubic arch and the arcuate ligament of the pubis
behind: the tip of the coccyx
on either side: the inferior rami of the pubis and Ischium, and the sacrotuberous ligament

In Alfred Kinsey's 1967 report, he concluded that the perineum was one of the 6 key erogenous zones for males.

Triangles

A line drawn transversely across in front of the ischial tuberosities divides the space into two triangles:

Name	Location	Contents
Urogenital triangle	the anterior triangle	in females, contains the vagina
Anal triangle	the posterior triangle	contains the anus

Perineal fascia

The terminology of the perineal fascia can be confusing, and there is some controversy over the nomenclature. This stems from the fact that there are two parts to the fascia, the superficial and deep parts, and each of these can be subdivided into superficial and deep parts.

The layers and contents are as follows, from superficial to deep:

1) Skin

2) superficial perineal fascia: Subcutaneous tissue divided into two layers: (a) A superficial fatty layer, and (b) Colles' fascia, a deeper, membranous layer.

3) deep perineal fascia and muscles:

superficial perineal pouch	Contains superficial perineal muscles: transversus perinei superficialis, bulbospongiosus, ischiocavernosus
inferior fascia of urogenital diaphragm, or perineal membrane	A membranous layer of the deep fascia.
deep perineal pouch	Contains the deep perineal muscles: transversus perinei profundus, sphincter urethrae membranaceae
superior fascia of the urogenital diaphragm	Considered hypothetical by some modern anatomists, but still commonly used to logically divide the contents of the region.

4) fascia and muscles of pelvic floor (levator ani, coccygeus)

Areas of the perineum

The region of the perineum can be considered a distinct area from pelvic cavity, with the two regions separated by the pelvic diaphragm. The following areas are thus classified as parts of the perineal region:

perineal pouches: superficial and deep (see above for details)
Ischioanal fossa - a fat filled space at the lateral sides of anal canal. It is bounded laterally by obturator internus muscle, medially by pelvic diaphragm and anal canal. Its base is the skin.