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Pelvic outlet

Bone: Pelvic outlet

Diameters of inferior aperture of lesser pelvis (female).

Muscles of the female perineum.
Latin	apertura pelvis inferior
Gray's	subject #58 240
Dorlands/Elsevier	a_51/12144712

The lower circumference of the lesser pelvis is very irregular; the space enclosed by it is named the inferior aperture or pelvic outlet.

Boundaries

It has the following boundaries:

These eminences are separated by three notches:

one in front, the pubic arch, formed by the convergence of the inferior rami of the ischium and pubis on either side.
The other notches, one on either side, are formed by the sacrum and coccyx behind, the ischium in front, and the ilium above; they are called the sciatic notches; in the natural state they are converted into foramina by the sacrotuberous and sacrospinous ligaments.

When the ligaments are in situ, the inferior aperture of the pelvis is lozenge-shaped, bounded as follows:

in front, by the pubic arcuate ligament and the inferior rami of the pubes and ischia
laterally, by the ischial tuberosities
behind, by the sacrotuberous ligaments and the tip of the coccyx.

v • d • e Bones of pelvis/pelvic cavity
General	sacrum, coccyx, hip bone
Ilium	Body (Arcuate line) Wing: gluteal lines (Posterior, Anterior, Inferior) - Fossa - iliac spines (Anterior superior, Anterior inferior, Posterior superior, Posterior inferior) - Crest - Tuberosity
Ischium	Body (Ischial spine, Lesser sciatic notch) - Superior ramus (Tuberosity of the ischium) - Inferior ramus
Pubis	Body - Superior ramus (Pubic tubercle, Pubic crest, Obturator crest) - Inferior ramus (Pectineal line)
Compound	Acetabulum (Acetabular notch) - Iliopubic eminence/Iliopectineal line - Linea terminalis - Ischiopubic ramus/Pubic arch Obturator foramen - Greater sciatic foramen/Greater sciatic notch - Lesser sciatic foramen Lesser pelvis (Pelvic inlet, Pelvic brim, Pelvic outlet) - Greater pelvis