The coccygeal vertebrae are the most inferior of the vertebrae.  They form part of the bony pelvis.  The vertebral features are poorly developed or missing.  The coccyx is usually 4 vertebrae although it varies from 2 to 5 vertebrae.  Normally the inferior vertebrae are fused together, while the first forms a amphiarthrosis with the fifth sacral vertebra.  In elderly people (60 or more years old) it may become fused to the sacrum.  Fusion of the coccygeal vertebrae occurs at variable rates, normally beginning by the mid twenties and reaching completion during later years.  It fuses at an earlier age in males than in females.  Because in males the coccyx continues the sacral curve, it can provide some support for pelvic viscera, although it points inferiorly in postpubescent females.  The coccyx serves as a point of attachment for some muscles.  It can be broken during a fall, or sometime during the delivery of a baby.  In nursery school we called it the tailbone.  It got its name from the thought by some anatomists that it resembled the beak of a cuckoo!  What party were they at?

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