Final answer:
The muscle not found in the upper extremity is the pectineus, which is located in the thigh. Biceps brachii, supinator, and brachialis are all upper extremity muscles. Therefore correct option is D
Step-by-step explanation:
The muscle that is NOT found in the upper extremity is the pectineus. The pectineus is a muscle situated in the upper part of the thigh, making it part of the lower extremity. In contrast, the biceps brachii, supinator, and brachialis muscles are all located in the upper extremity, which includes the shoulder, arm, forearm, and hand. For example, the biceps brachii and brachialis muscles work to flex the forearm. Moreover, the supinator is responsible for the supination of the forearm, turning it anteriorly.