Located above or on top of the main axis of the body, especially referring to muscles in fish and other animals that sit above the backbone.
From Greek 'epi' (upon) + 'axial' (relating to an axis). The term developed in comparative anatomy in the 19th century to describe muscle groups positioned dorsally relative to the vertebral column.
Fish use their epaxial muscles to swim—they're the powerful myomere blocks that let salmon leap upstream and eels twist through water! Understanding epaxial vs. hypaxial muscles revolutionized how scientists studied vertebrate evolution and movement.
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