Pelvic outlet
Encyclopedia
The lower circumference of the lesser pelvis
is very irregular; the space enclosed by it is named the inferior aperture or pelvic outlet.
-shaped, bounded as follows:
Lesser pelvis
The lesser pelvis is that part of the space enclosed by the skeleton of the pelvis which is situated between the pelvic inlet and the pelvic floor. Some authors call this cavity the pelvic cavity...
is very irregular; the space enclosed by it is named the inferior aperture or pelvic outlet.
Boundaries
It has the following boundaries:- anteriorly: the pubic arch
- laterally: the ischial tuberosities
- posterolaterally: the inferior margin of the sacrotuberous ligament
- posteriorly: the tip of the coccyxCoccyxThe coccyx , commonly referred to as the tailbone, is the final segment of the vertebral column. Comprising three to five separate or fused vertebrae below the sacrum, it is attached to the sacrum by a fibrocartilaginous joint, the sacrococcygeal symphysis, which permits limited movement between...
Notches
These eminences are separated by three notches:- one in front, the pubic archPubic archThe eminences of the lower circumference of the true pelvis 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 angle at which they converge is known as the subpubic angle.-External links:* *...
, formed by the convergence of the inferior rami of the ischium and pubisPubis (bone)In vertebrates, the pubic bone is the ventral and anterior of the three principal bones composing either half of the pelvis.It is covered by a layer of fat, which is covered by the mons pubis....
on either side. - The other notches, one on either side, are formed by the sacrumSacrumIn vertebrate anatomy the sacrum is a large, triangular bone at the base of the spine and at the upper and back part of the pelvic cavity, where it is inserted like a wedge between the two hip bones. Its upper part connects with the last lumbar vertebra, and bottom part with the coccyx...
and coccyxCoccyxThe coccyx , commonly referred to as the tailbone, is the final segment of the vertebral column. Comprising three to five separate or fused vertebrae below the sacrum, it is attached to the sacrum by a fibrocartilaginous joint, the sacrococcygeal symphysis, which permits limited movement between...
behind, the ischium in front, and the iliumIlium (bone)The ilium is the uppermost and largest bone of the pelvis, and appears in most vertebrates including mammals and birds, but not bony fish. All reptiles have an ilium except snakes, although some snake species have a tiny bone which is considered to be an ilium.The name comes from the Latin ,...
above; they are called the sciatic notches; in the natural state they are converted into foramina by the sacrotuberous and sacrospinous ligamentSacrospinous ligament-External links: - "Posterior view of the bones and ligaments of the hip joint."*...
s.
In situ
When the ligaments are in situ, the inferior aperture of the pelvis is lozengeLozenge
A lozenge , often referred to as a diamond, is a form of rhombus. The definition of lozenge is not strictly fixed, and it is sometimes used simply as a synonym for rhombus. Most often, though, lozenge refers to a thin rhombus—a rhombus with acute angles of 45°...
-shaped, bounded as follows:
- in front, by the pubic arcuate ligament and the inferior rami of the pubes and ischiaIschiaIschia is a volcanic island in the Tyrrhenian Sea. It lies at the northern end of the Gulf of Naples, about 30 km from the city of Naples. It is the largest of the Phlegrean Islands. Roughly trapezoidal in shape, it measures around 10 km east to west and 7 km north to south and has...
- laterally, by the ischial tuberosities
- behind, by the sacrotuberous ligaments and the tip of the coccyxCoccyxThe coccyx , commonly referred to as the tailbone, is the final segment of the vertebral column. Comprising three to five separate or fused vertebrae below the sacrum, it is attached to the sacrum by a fibrocartilaginous joint, the sacrococcygeal symphysis, which permits limited movement between...
.