Identify the phrenic nerve [left upper probe under C 3,4 fibers joining fibers of C5] as it courses along the anterior surface of scalenus anterior muscle with the ascending cervical artery. Trace this artery proximally to the point at which it arises from the thyrocervical trunk or the inferior thyroid artery.
The phrenic nerve lies posterior to the transverse cervical artery and suprascapular artery as they cross the anterior surface
of the scalenus anterior muscle.
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