A small sesamoid bone (a tiny independent bone) found in some animals, particularly in the knee joint of certain mammals.
From Latin fabella, the diminutive of faba meaning 'small bean,' because the bone's shape resembles a small bean. Medical term adopted into English anatomy.
The fabella is disappearing from humans—comparative anatomy shows more of us are born without it, suggesting our bodies are actually evolving in real time as this tiny bone becomes less necessary.
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