Infraspinatus

The Infraspinatus muscle is a thick triangular muscle, which occupies the chief part of the infraspinatous fossa bone of the shoulder.

Anatomy of the Infraspinatus

The Infraspinatus muscle attaches medially to the infraspinous fossa of the scapula and laterally to the greater tubercle of the humerus.

The Infraspinatus muscle arises by fleshy fibers from its medial two-thirds, and by tendinous fibers from the ridges on its surface; it also arises from the infraspinatous fascia which covers it, and separates it from the Teres major and minor.

The fibers converge to a tendon, which glides over the lateral border of the spine of the scapula, and, passing across the posterior part of the capsule of the shoulder-joint, is inserted into the middle impression on the greater tubercle of the humerus.

Functions of the Infraspinatus

The Infraspinatus muscle is an external rotator of the shoulder joint and adductor of the arm.

Together with the Teres Minor, the Infraspinatus rotates the head of the humerus outward (external rotation); they also assist in carrying the arm backward.

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