Pronator teres

Origin: Humeral head: medial epicondyle of humerus (common flexor tendon) - ulnar head: coronoid process of the ulna

Insertion: Radius

Artery: Ulnar artery and radial artery

Nerve: Median nerve

Action: Pronation of forearm, flexes elbow

Antagonist: Supinator muscle

Description:
The Pronator teres has two heads of origin—humeral and ulnar. The humeral head, the larger and more superficial, arises immediately above the medial epicondyle, and from the tendon common to the origin of the other muscles; also from the intermuscular septum between it and the Flexor carpi radialis and from the antibrachial fascia. The ulnar head is a thin fasciculus, which arises from the medial side of the coronoid process of the ulna, and joins the preceding at an acute angle. The median nerve enters the forearm between the two heads of the muscle, and is separated from the ulnar artery by the ulnar head. The muscle passes obliquely across the forearm, and ends in a flat tendon, which is inserted into a rough impression at the middle of the lateral surface of the body of the radius. The lateral border of the muscle forms the medial boundary of a triangular hollow situated in front of the elbow-joint and containing the brachial artery, median nerve, and tendon of the Biceps brachii.
Variations.—Absence of ulnar head; additional slips from the medial intermuscular septum, from the Biceps and from the Brachialis anticus occasionally occur.