Plural of apophysis; small projections, outgrowths, or processes on bones where tendons and muscles attach.
From Greek apophysis (off-growth), the plural form established in anatomical nomenclature. The Greek root apo- (away) plus physis (growth) perfectly describes these structural features.
Paleontologists can tell how strong ancient dinosaurs were by studying the size of their apophyses—huge muscle attachment points meant enormous muscles, which tells us T. rex was an active hunter rather than a scavenger.
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