superior thoracic aperture
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su·pe·ri·or tho·rac·ic ap·er·ture[TA]
the upper boundary of the bony thorax composed of the first thoracic vertebra and the upper margins of the first ribs and manubrium of the sternum. Note: clinicians refer to the superior thoracic aperture as the "thoracic outlet." as in "thoracic outlet syndrome."