Acetabulum.

http://www.thefreedictionary.com/acetabulum

1. Anatomy The cup-shaped cavity at the base of the hipbone into which the ball-shaped head of the femur fits.
2. Zoology A cavity or socket in the body of an insect into which an appendage fits.
3. Zoology A cup-shaped structure, such as the sucker of a tapeworm or leech.

Hip-joint, front view.

http://en.wikipedia.org/wiki/Acetabulum

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

http://en.wikipedia.org/wiki/Acetabulum

Symphysis pubis exposed by a coronal section.

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Plan of ossification of the hip bone.

http://en.wikipedia.org/wiki/Acetabulum

Right hip bone. External surface.

http://en.wikipedia.org/wiki/Acetabulum

"little vinegar cup".

http://en.wikipedia.org/wiki/Acetabulum

History

The word acetabulum literally means "little vinegar cup". It was the Latin word for a small vessel for serving vinegar. The word was later also used as a unit of volume.