胸廓上口 - Apertura thoracis superior
The superior thoracic aperture (thoracic inlet, upper opening of the thorax) is reniform in shape, being broader from side to side than from before backward. It is formed by the first thoracic vertebra behind, the upper margin of the sternum in front, and the first rib on either side. It slopes downward and forward, so that the anterior part of the opening is on a lower level than the posterior. Its antero-posterior diameter is about 5 cm., and its transverse diameter about 10 cm.
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