The supra-spinatus muscle (French: Muscle supra-épineux) is named from its position above the spine of the scapula. It is a somewhat fan-shaped, thick triangular sheet.

Origin

• The inner two-thirds of the supraspinous fossa;
• the upper surface of the spine of the scapula ; and (3) the fascia covering the muscle.

Insertion

The upper facet of the greater tuberosity of the humerus ; and the capsular ligament of the shoulder joint.

Structure

It arises by fleshy fibres which converge upon a tendon which is concealed in the substance of the muscle almost to the point of its insertion.

Nerve-supply

From the brachial plexus (through the fifth cervical nerve) by the suprascapular branch which enters the muscle upon its deep aspect near its upper border.

Action

It assists the deltoid in abducting the arm ; it also strengthens the shoulder joint by resisting the tendency to upward displacement of the head of the humerus, and by drawing the head of the humerus firmly tow^ards the centre of the glenoid cavity.

Relations

Superficially, the trapezius, deltoid, and coraco- acromial ligament ; deeply, the omo-hyoid muscle and capsular ligament, the suprascapular vessels and nerve.

Variations

It occasionally receives part of the tendon of the pectoralis minor.