The deltoid muscle (musculus deltoideus) is thick and triangular, covering the shoulder-joint, with the base facing upwards and the apex downwards. It is made up of large muscle fibers which converge fan-wise at the apex on lateral aspect of arm.
The deltoid muscle arises from the lateral portion of clavicle and superior and lateral surface of acromium (scapula). Its converging fibers run downwards to be inserted into the deltoid tuberosity of humerus. A large subdeltoid, or subacromial, bursa is lodged between the inferior surface of the muscle and the greater tuberosity of humerus. A bursa is a fluid-filled sac which functions to reduce friction.
Action
This powerful triangular muscle abducts the arm to the horizontal level (it pulls it laterally, extending it outwardly). It also pulls the arm forwardly and pronates it slightly.
Innervation
The deltoid muscle is innervated by the axillary nerve, which originates from the brachial plexus posterior cord.
Blood supply
It receives oxygenated blood from the posterior circumflex humeral, acromiothoracic, and deep brachial artery.
Below, the deltoid and other muscles of arm
