The pronator teres (or pronator teres muscle, latin: musculus pronator teres) is a quadrangular, superficial muscle that belongs to the anterior muscle group of the forearm and lies in the first, most superficial layer.
The pronator teres has two heads: the humeral and ulnar. The humeral head originates from the medial epicondyle of humerus, but the ulnar head of the pronator teres originates from the coronoid process of ulna. The pronator teres passes obliquely to the lateral side of the forearm and ends in a flat tendon that inserts on the middle of the lateral and posterior surface of the radius.
As all ventral muscles of the forearm, the pronator teres participates in flexion, in this case, the flexion of the forearm. Another function of the pronator teres is pronation of the forearm.