Medium staircase
Middle staircase , m. Scalenus medius, begins from the anterior tubercles of the six upper cervical vertebrae, is directed downward behind the anterior staircase and is attached to the upper surface of the I rib, behind the furrow of the subclavian artery. Above this groove, between the anterior and middle staircases, there is a triangular slit, in which the subclavian artery lies, a. Subclavia, and nerve trunks of the brachial plexus, nn. Plexus brachialis.
Function: with a strengthened spinal column, I lifts the rib; With a strengthened thorax, it tilts the cervical spine forward.
Innervation: nn. Cervicales (C3-C7).
Blood supply: aa. Vertebralis, cervicalis profunda.
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