<s>[INST] context: The subclan aery passes laterally over the upper surface of the first rib and lies posterior to the scalenus anterior. In the case of thoracic outlet syndrome, this aery is usually compressed between the scalenus anterior and a cervical rib. Thoracic outlet syndrome is a broad term for a group of disorders in which there is compression of ceain neurovascular bundles. The presence of a cervical rib adds to the compression, and repetitive motion and poor posture are other predisposing factors. When the neurovascular bundle is entrapped, the patient presents with neurological and/or circulatory changes in the upper extremity on the involved side.The axillary aery is the continuation of the subclan aery. This aery begins at the outer border of the first rib and continues through the axilla to the lower border of the teres major.The brachial aery is the continuation of the axillary aery in the upper extremity and can not be compressed by a cervical rib.The brachiocephalic aery arises from the arch of the aoa. At the level of the right sternoclavicular joint, it separates into the right common carotid aery and the right subclan aery. [/INST] question: A 50 year old electrician repos pain in his left upper extremity and tingling and numbness in his 4th and 5th digits of his left hand. There is mild swelling of the left hand. The man repos most of his pain and numbness occurs when he is doing electrical work with his arms overhead. X-ray reveals the presence of a cervical rib. Which of the following structures is most likely being compressed? | options: A: Axillary aery B: Brachial aery C: Brachiocephalic aery D: Subclan aery | answer: D </s>