Teres Major Muscle Anatomy

The Teres Major Muscle (L. teres, round) is relatively short muscles that pass from the scapula to the humerus and act on the glenohumeral joint.

Teres Major Muscle Anatomy

The Teres Major Muscle is a thick, rounded muscle passing laterally from the inferolateral third of the scapula. The inferior border of the teres major forms the inferior border of the lateral part of the posterior wall of the axilla.

Origin and Insertion

The teres major originates from the dorsal surface of the inferior angle and the lower third of the lateral border of the scapula. This origin provides a robust attachment point that contributes to the muscle’s mechanical advantage. The muscle fibers course laterally and slightly superiorly, converging into a thick tendon that inserts into the medial lip of the intertubercular groove of the humerus. This insertion point is notably distinct from but adjacent to the latissimus dorsi insertion, with which it shares functional synergy.

Neurovascular Supply

The lower subscapular nerve, derived from the posterior cord of the brachial plexus (C6-C7), provides primary innervation to the teres major. This neural architecture explains the muscle’s complex role in shoulder mechanics and its coordination with other shoulder girdle muscles.

The arterial supply primarily comes from the subscapular artery and its circumflex scapular branch, ensuring adequate blood flow for optimal muscle function.

See Also: Brachial Plexus Anatomy

Function & Action

Understanding the biomechanical actions of the teres major requires appreciation of its unique fiber orientation and attachment points. The muscle functions primarily as an internal rotator and adductor of the humerus. When acting in concert with the latissimus dorsi, it provides powerful extension of the glenohumeral joint. This functional relationship has earned the teres major the colloquial designation “little lat,” reflecting its synergistic action with the latissimus dorsi.

Clinical Significance

The muscle commonly experiences adaptive shortening in patients with poor posture or repetitive overhead activities. Additionally, its proximity to the quadrangular space makes it an important consideration in quadrangular space syndrome diagnosis. Distinguishing teres major pathology from rotator cuff injuries requires careful clinical examination and understanding of referred pain patterns.

To test the teres major (or the lower subscapular nerve that supplies it), the abducted arm is adducted against resistance. If acting normally, the muscle can be easily seen and palpated in the posterior axillary fold

References & More

1. Gray’s Anatomy: The Anatomical Basis of Clinical Practice https://www.elsevier.com/books/grays-anatomy/standring/978-0-7020-5230-9
2. Clinically Oriented Anatomy – 8th Edition