Pelvis

See also Human pelvis for extensive details.

The pelvic girdle of Falcarius utahensis

The pelvis, derived from the Latin word for 'basin', is an anatomical structure found in most vertebrates. It is the name given to both a bony structure or pelvic girdle connecting the base of the spine to the rear limbs, and the region of the body defined by that structure. The muscles and tissue beneath the pelvic girdle are known as the pelvic floor.

Pelvis skeleton

The pelvic girdle is also known as the pelvis skeleton or bony pelvis. It is a large, bilaterally symmetric, compound bone structure, consisting of the os coxa, sacrum and coccyx. The top or forward part of the pelvis is called the pelvic inlet, and its edge the pelvic brim. A related skeletal structure, found mainly in birds and dinosaurs, is the synsacrum.

In mammals, the pelvic girdle has a gap in the middle, significantly larger in females than in males. Babies pass through this gap when they are born.

Pelvic cavity and lesser pelvis

The cavity defined by the pelvic girdle up to the pelvic brim is known as the pelvic cavity. The region of the body defined by the pelvic girdle and the pelvic cavity is called the lesser pelvis (or true pelvis).

As the pelvis is concave, another cavity is defined by the pelvis above and in front of the pelvic brim. This is referred to this as the greater pelvis (or false pelvis). Some authors consider it part of the pelvic cavity, others consider it part of the abdominal cavity, others call both the abdominopelvic cavity.

Evolutionary history

The pelvis can be traced back to the pelvic girdles of early vertebrates, and to the paired fins of fish that were some of the earliest chordates.