The pelvis (pl. pelvises or pelves) or pelvic girdle is the irregular bony structure located at the base of the spine (properly known as the caudal end). In the adult human, it is formed by the sacrum and the coccyx, the caudal part of the axial skeleton, and a pair of hip bones, part of the appendicular skeleton or lower extremity. Until puberty, however, each hip bone consist of three separate bones yet to be fused — the ilium, ischium, and the pubis — and the pelvis is thus composed of up to five or seven bones.

The ilium is the largest and upper most part, the ischium is the posterior-inferior (back-lower) part, and the pubis is the anterior (front) part of the hip bone. The two hip bones are joined anteriorly at the symphysis pubis and posteriorly to the sacrum. The pelvis incorporates the socket portion of the hip joint (the acetabulum) for each leg (in bipeds) or hind leg (in quadrupeds). It forms the lower limb (or hind-limb) girdle of the skeleton.

Pelvic cavity

The lesser pelvis (or "true pelvis") only includes structures inferior to the pelvic brim.

The greater pelvis (or "false pelvis") is the expanded portion of the cavity situated above and in front of the pelvic brim.

Sex differences

main: Sex differences in humans

• Infrapubic angle is greater than 90˚ in females and less than 90˚ in males.
• Pelvic inlet in males is more heart-shaped, while in females it is more round or oval.
• Greater sciatic notch narrower in males.
• Acetabulum in males faces more laterally, while it faces more anteriorly in females.
• Sacrum more triangular and shorter in females.

There are four main types of pelvis

• Gynaecoid: Normal female pelvis, round with enlarged transverse diameter
• Android: Normal male pelvis, Heart shaped
• Anthropoid: Long anterior to posterior diameter
• Platypelloid: Long transverse diameter

Biiliac width

In humans, biiliac width is an anatomical term referring to the widest measure of the pelvis between the outer edges of the upper iliac bones.

Biiliac width has the following common synonyms: pelvic bone width, biiliac breadth, intercristal breadth/width, bi-iliac breadth/width and biiliocristal breadth/width.

In the average adult female, it measures 28 cm (11 in).fact: date=October 2008 It is best measured by anthropometric calipers (an anthropometer designed for such measurement is called a pelvimeter). Attempting to measure biiliac width with a tape measure along a curved surface is inaccurate.

The biiliac width measure is helpful in obstetrics because a pelvis that is significantly too small or too large can have obstetrical complications. For example, a large baby and/or a small pelvis often lead to a caesarean section.