The tailbone, the small triangular bone at the very end of the spine
Coccyx — usually four fused coccygeal vertebrae.
Anatomy · Bones
Coccyx
The tailbone
Pelvis · spine
The coccyx, or tailbone, is the small triangular bone at the very bottom of the spine, formed by the fusion of usually four small coccygeal vertebrae. It articulates with the apex of the sacrum and is a vestigial remnant of the tails of our distant ancestors. It gives attachment to muscles, ligaments and the pelvic floor.
How to spot them
- ▸A small, curved, triangular bone hanging below the sacrum at the base of the spine
- ▸Made of three to five (usually four) fused, rudimentary vertebrae with no vertebral canal or arches
- ▸Small projections, the coccygeal cornua, on the first segment articulate with the sacral cornua
- ▸Its tip is a rounded prominence where muscles and ligaments of the pelvic floor attach
What to know
Its Greek name means a cuckoo, from the resemblance of the bone to the bird's beak
Coccyx — from the Greek kokkyx, cuckoo.
The vestigial remnant of the tail: humans, like the other apes, have no external tail, but this small bone is what is left of it
Coccyx — the human tail remnant.
Painful after a fall onto the bottom or after childbirth, this small bone is a common cause of persistent pain when sitting
Coccyx — coccydynia.
It has no vertebral canal or vertebral arches, unlike the bone above it
Coccyx — recognised by absent canal and arches.
It articulates with the apex of the sacrum at a joint that may fuse with age
Coccyx — the sacrococcygeal joint.
Its rounded tip is an anchoring point for the muscles and ligaments of the pelvic floor
Coccyx — an attachment for levator ani and the anococcygeal ligament.
Key ideas
- The coccyx is formed of three to five fused vertebrae, most commonly four, and the number varies between individuals.
Quick-fire facts
- •Usually four small coccygeal vertebrae fuse to form it
- •It has no vertebral canal or vertebral arches
- •It articulates with the sacrum at the sacrococcygeal joint
- •The coccygeal cornua of Co1 articulate with the sacral cornua and form a foramen for the posterior division of the fifth sacral nerve
- •Its tip is an attachment site for muscles and ligaments of the pelvic floor
- •Coccydynia is the term for pain in the coccyx
- •Kokkyx is Greek for cuckoo, and the coccyx was so named for its resemblance to a cuckoo's beak
- •The sacrum and coccyx are the 'false' vertebrae because they are fused
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Sources
- Kenhub — Coccyx: Anatomical structure and function
- TeachMeAnatomy — The Vertebral Column
- OpenStax — Anatomy and Physiology 2e, 7.3 The Vertebral Column