A small triangular bone at the base of the spinal column in humans and some apes, formed of fused vestigial vertebrae.‘The sacrum itself represents 5 fused bones, and the coccyx another vestigial 2-3 or more - the remains of the ancestral tail.’
- ‘The spinal column is composed of seven cervical vertebrae, twelve thoracic vertebrae, five lumbar vertebrae, the bony sacrum, and the coccyx.’
- ‘Many of my patients have pressure ulcers on the coccyx or sacrum.’
- ‘From splintered bones in the coccyx, she was bedridden for nearly two years.’
- ‘For that matter an injury to the spine or the coccyx also qualifies as affecting the automatic nervous system.’
Late 16th century via Latin from Greek kokkux ‘cuckoo’ (because the shape of the human bone resembles the cuckoo's bill).
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