Subclan aery is divided by which muscle ?

Ans. is 'c' i.e., Scaleneus anterior Scaleneus anterior muscle divides subclan aery into three pas :?A) First pa :This pa is medial (proximal) to scaleneus anterior. Branches from first pa are :?Veebral aeryInternal thoracic aeryThyrocervical trunk:Costocervical trunk (on left side only).B) Second pa :This pa lies posterior to scalenus anterior. It gives origin to Costocervical trunk on right side. Costocervical trunk gives following branches:Deep cervical aerysuperior intercostal aery.C) Third pa :This pa lies lateral (distal) to scalenus anterior. It gives dorsal scapular aery (sometimes dorsal scapular aery arises from transverse cervical aery, a branch of thyrocervical trunk).