This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Anatomy
In a subclan aery block at outer border of 1st rib, all of the following aeries help in maintaining the circulation to upper limb, EXCEPT? 
Select and explain. 
A. Subscapular aery, B. Superior thoracic aery, C. Thyrocervical trunk, D. Suprascapular aery
B: Superior thoracic aery
Answer: B: Superior thoracic aery 
Explanation: A rich anastomosis exists around the scapula between branches of subclan aery (first pa) and the axillary aery (third pa). This anastomosis provides a collateral circulation through which blood can flow to the limb when the distal pa of subclan aery or the proximal pa of axillary aery is blocked. Scapular anastomoses occur between the following branches of proximal subclan and distal axillary aery: Branches of Subclan aery: Thyrocervical trunk, Suprascapular and Deep branch of transverse cervical.Branches of Axillary aery: Subscapular, Posterior circumflex humeral and Thoracoacromial aeires.