Exposure of left subclavian artery by supraclavicular approach does not require cutting of -
Scalenus anterior muscle is cut to approach subclavian artery (2nd part). However, scalenus medius need not be divided as it lies posteroinferior to the subclavian artery.
Platysma, sternocleidomastoid, sternothyroid and sternohyoid muscle are anterior to 1st part; scalenus anterior (along with SCM and platysma) muscle is anterior to 2nd part; and subclavius (along with SCM and platysma is anterior to the 3rd part of the subclavian artery. Whereas, inferior belly of omohyoid is superior, and scalenus medius is posterior to the 3rd part of the subclavian artery.
Sternocleidomastoid
Scalenus anterior
Scalenus medius
Omohyoid