A broad, flat fibrous sheet of tissue that attaches a muscle to bone or another muscle, functioning like a flat tendon or fascia.
From Greek apo- 'away from' + neuron 'sinew' + -osis (condition). The term emerged in Renaissance anatomical texts to describe these sheet-like structures that early anatomists distinguished from thicker tendons.
Your aponeurosis is what lets you have smooth, expressive movements—instead of thick muscle tendons everywhere, these flat sheets spread muscle force gently, which is why your forehead can wrinkle smoothly instead of in jagged lines.
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