# Urogenital Triangle and Perineal Pouches

> Perineal membrane, superficial and deep perineal pouches, urethral rupture patterns and Bartholin glands for MBBS Anatomy.

- Canonical URL: https://prepelephant.com/topics/mbbs/anatomy/urogenital-triangle
- Exam / course: MBBS · Subject: Anatomy
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-02
- Last updated: 2026-10-02
- How to cite: "Urogenital Triangle and Perineal Pouches", PrepElephant, https://prepelephant.com/topics/mbbs/anatomy/urogenital-triangle

## Direct answer

A tough triangular membrane, the perineal membrane, stretches across the pubic arch of the urogenital triangle and divides it into a superficial perineal pouch below, containing the erectile bodies of the penis or vulva with their muscles, and a deep pouch above, containing the voluntary external urethral sphincter and deep transverse perineal muscles. The membrane is pierced by the urethra in the male and by urethra and vagina in the female, and the level of piercing decides the surgery: a straddle injury ruptures the bulbar urethra below the membrane so urine floods the superficial pouch in a butterfly pattern, while a pelvic fracture shears the membranous urethra above it and urine dissects deep to it.

## What you must remember

- **Perineal membrane:** the inferior fascia of the urogenital diaphragm, a triangular sheet attached to the ischiopubic rami, its posterior edge merging with the perineal body.
- **Deep perineal pouch:** between the superior and inferior fasciae of the urogenital diaphragm; contains the external urethral sphincter (sphincter urethrae) and deep transverse perineal muscles, the bulbourethral glands in the male, and transmits the internal pudendal vessels and dorsal nerves laterally.
- **Superficial perineal pouch:** below the membrane, roofed by it and floored by Colles fascia; contains in the male the bulb and crura with bulbospongiosus and ischiocavernosus, and in the female the vestibular bulbs, Bartholin glands, crura of the clitoris and the same muscles.
- **External urethral sphincter:** voluntary striated muscle supplied by the pudendal nerve S2 to S4; in the female augmented by the compressor urethrae and urethrovaginal sphincter.
- **Colles fascia attachments:** posteriorly to the posterior edge of the perineal membrane and perineal body, laterally to the ischiopubic rami and fascia lata, and anteriorly continuous with dartos and Scarpa's fascia — the boundaries that shape extravasation.
- **Bulbar urethral rupture (straddle injury):** urine and blood fill the superficial pouch and spread to scrotum, penis and anterior abdominal wall, but never to the anal triangle or thighs.
- **Bartholin glands:** great vestibular glands in the posterior superficial pouch, ducts opening into the vestibule between hymen and labium minus at about the five and seven o'clock positions; cysts and abscesses are treated by marsupialisation.

## Two urethral ruptures, two diagrams

A young man falls astride a fence and presents with perineal bruising, blood at the meatus and retention. The bulb of the penis was crushed against the pubic arch, tearing the bulbar urethra below the perineal membrane. Urine escapes into the superficial perineal pouch, and Colles fascia's attachments dictate its map: blocked behind at the perineal membrane's posterior edge and laterally at the rami, the collection butterfly-spreads over the perineum, then forwards into scrotum and penis and up the anterior abdominal wall beneath Scarpa's fascia — everything except the anal triangle and thighs.

The second man is hit by a car and has a pelvic fracture with a high-riding prostate on rectal examination, blood at the meatus and no urine: his membranous urethra, fixed in the perineal membrane, sheared off the prostatic apex. Urine and blood dissect above the membrane into the extraperitoneal pelvic space. The rule between the two is absolute: no catheter is passed before urethrography in a suspected membranous rupture, because a partial tear can be converted into a complete one.

## Where students slip

The urogenital diaphragm is drawn as a solid slab with two fasciae and muscle between; modern texts describe the perineal membrane with sphincter muscles above it, and examiners now prefer that framing. The bulbourethral glands of Cowper are placed in the superficial pouch; they lie in the deep pouch, their ducts travelling forward to open into the bulbar urethra. In the female, the vestibular bulbs and Bartholin glands are forgotten because most dissection teaching is male — precisely the structures a Bartholin abscess brings to the emergency department.

## Frequently asked questions

### What is the perineal membrane and what is attached to it?

The inferior fascia of the urogenital diaphragm spanning the ischiopubic rami; the external urethral sphincter and deep transverse perineal muscles sit above it, and Colles fascia anchors to its posterior edge.

### What does the deep perineal pouch contain?

The external urethral sphincter, deep transverse perineal muscles and the bulbourethral glands in the male, with the internal pudendal vessels and dorsal nerves crossing its lateral wall.

### Why does urine from a ruptured bulbar urethra not reach the thighs?

Colles fascia attaches laterally to the ischiopubic rami and the fascia lata of the thigh, confining extravasated urine to the perineum, scrotum, penis and anterior abdominal wall.

### How does membranous urethral rupture differ from bulbar rupture?

Membranous rupture accompanies pelvic fracture, shears the urethra above the perineal membrane and dissects urine extraperitoneally deep to it, with a high-riding prostate; bulbar rupture is a straddle injury confined to the superficial pouch.

### Where do the Bartholin glands lie and open?

In the posterior part of the superficial perineal pouch, with ducts opening into the vestibule between the hymen and the labium minus at about five and seven o'clock.