The pelvic brim is the edge of the pelvic inlet

Pelvic inlet

The pelvic inlet or superior aperture of the pelvis is a planar surface which is typically used to define the boundary between the pelvic cavity and the abdominal cavity .Its position and orientation relative to the skeleton of the pelvis is anatomically defined by its...

. It is an approximately apple-shaped line passing through the prominence of the sacrum

Sacrum

In 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...

, the arcuate

Arcuate line (ilium)

The arcuate line of the ilium is a smooth rounded border on the internal surface of the ilium. It is immediately inferior to the iliac fossa and Iliacus muscle.It forms part of the border of the pelvic inlet....

 and pectineal line

Pectineal line (pubis)

The pecten pubis or pectineal line of the pubis is a ridge on the superior ramus of the pubic bone.The pecten pubis forms part of the pelvic brim.Lying across it are fibers of the pectineal ligament and the proximal origin of the pectineus muscle....

s, and the upper margin of the pubic symphysis

Pubic symphysis

The pubic symphysis or symphysis pubis is the midline cartilaginous joint uniting the superior rami of the left and right pubic bones. It is located anterior to the urinary bladder and superior to the external genitalia; for females it is above the vulva and for males it is above the penis...

.

The pelvic brim is somewhat apple-shaped, obtusely pointed in front, diverging on either side, and encroached upon behind by the projection forward of the promontory of the sacrum

Sacrum

In 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...

.

The oblique plane passing approximately through the pelvic brim divides the internal part of the pelvis

Pelvis

In human anatomy, the pelvis is the lower part of the trunk, between the abdomen and the lower limbs .The pelvis includes several structures:...

 (pelvic cavity

Pelvic cavity

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) into the false or greater pelvis

Greater pelvis

The greater pelvis is a portion of the cavity surrounded by the skeleton of the pelvis, situated above and in front of the pelvic brim...

 and the true or lesser pelvis

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...

. The false pelvis, which is above that plane, is sometimes considered to be a part of the abdominal cavity

Abdominal cavity

The abdominal cavity is the body cavity of the human body that holds the bulk of the viscera. It is located below the thoracic cavity, and above the pelvic cavity. Its dome-shaped roof is the thoracic diaphragm , and its oblique floor is the pelvic inlet...

, rather than a part of the pelvic cavity (see also Abdomen

Abdomen

In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...

). In this case, the pelvic cavity coincides with the true pelvis, which is below the above-mentioned plane.