The lower circumference of the

lesser pelvis The pelvic cavity is a body cavity that is bounded by the bones of the pelvis. Its oblique roof is the pelvic inlet (the superior opening of the pelvis). Its lower boundary is the pelvic floor. The pelvic cavity primarily contains the reproduc ...

is very irregular; the space enclosed by it is named the inferior aperture or pelvic outlet. It is an important component of

pelvimetry Pelvimetry is the measurement of the female human pelvis, pelvis. It can theoretically identify cephalo-pelvic disproportion, which is when the capacity of the pelvis is inadequate to allow the fetus to negotiate the birth canal. However, clinical ...

Boundaries

It has the following boundaries: * anteriorly: the

pubic arch The pubic arch, also referred to as the ischiopubic arch, is part of the pelvis. It is formed by the convergence of the inferior rami of the ischium and pubis on either side, below the pubic symphysis. The angle at which they converge is known a ...

* laterally: the

ischial tuberosities The ischial tuberosity (or tuberosity of the ischium, tuber ischiadicum), also known colloquially as the sit bones or sitz bones, or as a pair the sitting bones, is a large posterior bony protuberance on the superior ramus of the ischium. It ...

* posterolaterally: the inferior margin of the sacrotuberous ligament * posteriorly: the anterior border of the middle of the

coccyx The coccyx (: coccyges or coccyxes), commonly referred to as the tailbone, is the final segment of the vertebral column in all apes, and analogous structures in certain other mammals such as horse anatomy, horses. In tailless primates (e.g. hum ...

Notches

These eminences are separated by three notches: * one in front, the

, formed by the convergence of the inferior rami of the

ischium The ischium (; : is ...

and pubis on either side. * The other notches, one on either side, are formed by the

sacrum The sacrum (: sacra or sacrums), in human anatomy, is a triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part of the pelvic cavity, ...

and

behind, the

ischium The ischium (; : is ...

in front, and the ilium above; they are called the sciatic notches; in the natural state they are converted into

foramina In anatomy and osteology, a foramen (; : foramina, or foramens ; ) is an opening or enclosed gap within the dense connective tissue (bones and deep fasciae) of extant and extinct amniote animals, typically to allow passage of nerves, arter ...

by the

sacrotuberous The sacrotuberous ligament (great or posterior sacrosciatic ligament) is situated at the lower and back part of the pelvis. It is flat, and triangular in form; narrower in the middle than at the ends. Structure It runs from the sacrum (the lower ...

and

sacrospinous ligament The sacrospinous ligament (small or anterior sacrosciatic ligament) is a thin, triangular ligament in the human pelvis. The base of the ligament is attached to the outer edge of the sacrum and coccyx, and the tip of the ligament attaches to the i ...

In situ

When the ligaments are in situ, the inferior aperture of the pelvis is

lozenge Lozenge or losange may refer to: * Lozenge (shape), a type of rhombus *Throat lozenge A throat lozenge (also known as a cough drop, sore throat sweet, troche, cachou, pastille or cough sweet) is a small, typically medicated tablet intended to ...

-shaped, bounded as follows: * in front, by the

pubic arcuate ligament The pubic symphysis (: symphyses) is a secondary cartilaginous joint between the left and right superior pubic ramus, superior rami of the pubis of the pubis (bone), hip bones. It is in front of and below the urinary bladder. In males, the suspens ...

and the

inferior rami of the pubes In vertebrates, the pubis or pubic bone () forms the lower and anterior part of each side of the hip bone. The pubis is the most forward-facing (ventral and anterior) of the three bones that make up the hip bone. The left and right pubic bones ar ...

and

ischia Ischia ( , , ) is a volcanic island in the Tyrrhenian Sea. It lies at the northern end of the Gulf of Naples, about from the city of Naples. It is the largest of the Phlegrean Islands. Although inhabited since the Bronze Age, as a Ancient G ...

* laterally, by the

* behind, by the

sacrotuberous ligaments The sacrotuberous ligament (great or posterior sacrosciatic ligament) is situated at the lower and back part of the pelvis. It is flat, and triangular in form; narrower in the middle than at the ends. Structure It runs from the sacrum (the lower ...

and the tip of the

Additional images

File:Gray319.png, Articulations of pelvis. Anterior view. File:Gray320.png, Articulations of pelvis. Posterior view. File:Low-dose CT of sagittal pelvic outlet diameter.jpg, Low-dose

CT scan A computed tomography scan (CT scan), formerly called computed axial tomography scan (CAT scan), is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers or ...

of sagittal pelvic outlet diameter as part of

File:Low-dose CT scan of intertuberous diameter.jpg, Intertuberous diameter, as a measure of the transverse measure of the pelvic outlet

References

External links