Article: Pelvis

The pelvis (pl. pelvises or pelves) is the bony structure located at the base of the spine (properly known as the caudal end). The pelvis incorporates the socket portion of the hip joint for each leg (in bipeds) or hind leg (in quadrupeds). It forms the lower limb (or hind-limb) girdle of the skeleton.

Components

Human male pelvis, viewed from front

Human female pelvis, viewed from front

Left hip-joint, opened by removing the floor of the acetabulum from within the pelvis.

The pelvis is symmetrical and each side is actually made up of three separate bones:

• the upper half (the broad "wings") is the ilium
• the middle (the top half of the lower "loops") is the pubis
• the bottom (the lower half of the "loops") is the ischium

These three bones fuse together with age and are collectively known as the hip bone, ossa coxae or the innominate bone. The pelvis is joined to the sacrum bone by ligaments (the sacroiliac joint), and the hip bones nest in specially shaped sockets (the acetabulum) on each side. The upper edge of the ilium is known as the iliac crest. The place at the front of the pelvis where the two sides join together is called the symphysis pubis. This is normally a very inflexible joint, but it softens and becomes more flexible during late pregnancy, allowing it to expand during labour for the baby's head to pass through.

Sexual differences

A female pelvis is also wider and shallower than a male pelvis. A well-known way of determining the sex of a pelvis is to compare the angle of the width of the frontal opening to one's hand.

• If the angle is about the same as between the outstretched thumb and index finger, it is a female pelvis (arcus pubis).
• If it is closer to the angle between the spread index and middle fingers, it is a male pelvis (arcus subpubis).

Function

The pelvis protects the digestive and reproductive organs in the lower part of the body, and many large nerves and blood vessels pass through it to supply the legs. It is also an important load-bearing part of the skeletal system.

See also

• Bone terminology
• Terms for anatomical location
• Hip fracture
• Lesser pelvis
• Greater pelvis
• Pelvic cavity