A small bony projection on a vertebra through which blood vessels pass, located on either side of the vertebral body.
From Greek 'hema' (blood) + 'apophysis' (an outgrowth), literally meaning 'blood-projection,' referring to the anatomical structure that facilitates blood vessel passage through the spine.
Fish were the first creatures to develop these structures 500 million years ago, and they're still present in human vertebrae—it's a reminder that our backbone evolved gradually from aquatic ancestors.
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