Pronator teres muscle

The pronator teres is a muscle of the human body (located mainly in the forearm) that, along with the pronator quadratus, serves to pronate the forearm (turning it so the palm faces downward).

Structure
The pronator teres has two heads--humeral and ulnar.

The humeral head, the larger and more superficial, arises immediately above the medial epicondyle of the humerus and from the common flexor tendon.

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, just below the insertion of the supinator.

The lateral border of the muscle forms the medial boundary of triangular hollow known as the cubital fossa, which is situated in front of the elbow-joint.

Innervation
The pronator teres is innervated by the median nerve.

Variations
Occasionally, the ulnar head is absent. Also, additional slips from the medial intermuscular septum, from the biceps brachii, and from the brachialis occasionally occur.

Clinical aspects
"Pronator teres syndrome" is one common cause of wrist pain.