Teres major muscle

At a glance

English

Teres major muscle

Latin (TA2)

Musculus teres major

System

Muscle

Region

Upper limb

Side

Paired, left and right

About the teres major muscle

Teres major is a stout, slightly flattened muscle at the back of the shoulder, forming part of the lower border of the posterior axillary fold together with latissimus dorsi. Its name, from the Latin for rounded, reflects its cylindrical shape. Although it sits beside the rotator cuff muscles, it is not one of them, because its tendon does not merge with the shoulder joint capsule.

It arises from an oval area on the back of the scapula at its inferior angle and along the lower lateral border. The fibres run upwards and outwards, pass in front of the long head of triceps and end in a flat tendon on the inner lip of the humerus's intertubercular groove. That tendon lies just behind the tendon of latissimus dorsi; a bursa separates the two, though they fuse along their lower edges for a short stretch. The two muscles run parallel and act much alike, so teres major is sometimes called the little helper of latissimus.

Teres major adducts and medially rotates the humerus and draws a raised arm down and back, as in a rowing stroke or climbing. It also helps keep the humeral head seated in the glenoid cavity. With the arm fixed, it can rotate the scapula.

The muscle forms a boundary of several spaces in the posterior shoulder. With teres minor above, the humerus laterally and the long head of triceps, it outlines the quadrangular space, which carries the axillary nerve and posterior circumflex humeral vessels, and the triangular space and interval nearby, which carry the circumflex scapular artery and the radial nerve. Isolated injury is unusual and seen mainly in throwing athletes.

Attachments, action and supply

Origin

Dorsal surface of the scapula at its inferior angle and along the lower lateral border.

Insertion

Inner (medial) lip of the humeral intertubercular groove.

Action

Adducts and medially rotates the arm and extends it from a raised position; steadies the humeral head.

Nerve supply

Lower subscapular nerve (C5, C6), a posterior cord branch; sometimes also the thoracodorsal nerve.

Blood supply

Circumflex scapular and thoracodorsal arteries, branches of the subscapular artery.