An extension of the body that projects beyond the anus in chordates, containing muscle, nerve cord, and notochord but no digestive organs. This tail is used primarily for locomotion and is a defining characteristic of the chordate phylum.
Descriptive anatomical term from Latin 'post' meaning 'after' and 'anus,' with 'tail' from Old English. This precise terminology was developed in comparative anatomy to distinguish the true muscular tail of chordates from other posterior body extensions.
Your tailbone (coccyx) is proof that you once had a post-anal tail as an embryo - it's evolution's leftover blueprint for the swimming tail that helped our ancient ancestors move through water! Even whales and dolphins still use this original chordate design for their powerful tail flukes.
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