<prompt> Subclan aery is divided by which muscle ?Pectoralis minorTeres minorScaleneus anteriorTrapezius  <response>: 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. 