Anatomy · Upper Limb

Deltoid muscle and axillary nerve

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Deltoid: thick, triangular muscle covering the shoulder, giving it its rounded contour; three parts, anterior, middle and posterior.
Axillary nerve (C5, C6): terminal branch of the posterior cord, supplying deltoid and teres minor.

Deltoid: Origin, Insertion and Action

V-shaped origin from the bony arch: lateral third of clavicle, acromion, and crest of spine of scapula.

Deltoid, origin and action by part

Part	Origin	Action
Anterior (clavicular), unipennate	Upper surface and anterior border of lateral third of clavicle	Flexion and medial rotation of arm
Middle (acromial), multipennate	Lateral margin and upper surface of acromion	Abduction of arm, 15° to 90°
Posterior (spinous), unipennate	Lower lip of crest of spine of scapula	Extension and lateral rotation of arm

Part

Anterior (clavicular), unipennate

Origin: Upper surface and anterior border of lateral third of clavicle
Action: Flexion and medial rotation of arm

Middle (acromial), multipennate

Origin: Lateral margin and upper surface of acromion
Action: Abduction of arm, 15° to 90°

Posterior (spinous), unipennate

Origin: Lower lip of crest of spine of scapula
Action: Extension and lateral rotation of arm