Vestigial Coccyx

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Live Science writes on the human coccyx: “These fused vertebrae are the only vestiges that are left of the tail that other mammals still use for balance, communication, and in some primates, as a prehensile limb. As our ancestors were learning to walk upright, their tail became useless, and it slowly disappeared. It has been suggested that the coccyx helps to anchor minor muscles and may support pelvic organs. However, there have been many well documented medical cases where the tailbone has been surgically removed with little or no adverse effects. There have been documented cases of infants born with tails, an extended version of the tailbone that is composed of extra vertebrae.”

Live Science

Editorial Comment: One of the editors of this newsletter has had the very painful and debilitating experience of tearing the ligaments from the coccyx and wrote in a previous Evidence news (11 June 2008): “when that happens - if you were standing (or sitting) – that's where you stayed, as the muscles that helped you sit or stand all gained their ability to move by their attachment to the tail bone, so to call it vestigial and without function – what a painfully false statement.”

The coccyx is part of a system of bones and ligaments that act as muscle attachment for the pelvic floor muscles and is only surgically removed if it has been badly damaged and can no longer function as part of the system.

We would like to know where Live Science found “documented cases of infants born with tails, an extended version of the tailbone that is composed of extra vertebrae.” There are documented cases of infants born with “caudal appendages,” which are birth defects caused by an overgrowth of skin and fibrous-fatty tissue near the base of the spine. These are sometimes associated with more serious developmental defects of the spine, or may be part of a tumour called a sacrococcygeal teratoma. Either way they are not functional or even partially functional tails with vertebral bones and attached muscles like an animal tail. (Ref. vestigial, teratology, orthopaedics)

Evidence News, 7 October 2009

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