Name

# Deltoid

Pronunciation

(DEL-toid)

Origin/Proximal Attachment

Anterior portion: anterior border of the lateral 1/3 of the clavicle Middle portion: lateral border of the acromion process of the scapula Posterior portion: scapular spine

Insertion/Distal Attachment

Deltoid tuberosity, on the lateral surface of the shaft of the humerus

Action/Relevance

Anterior portion: flexes & internally rotates the armMiddle portion: abducts the armPosterior portion: extends & externally rotates the arm

Innervation

Axillary nerve (C5, 6)

Notes

The deltoid muscle is the muscle forming the rounded contour of the human shoulder.

It was earlier called as the Deltoideus and the name is still used by some anatomists. It is called so because it is in the shape of the Greek letter Delta (triangle).

The deltoid is a frequent site to administer intra-muscular injections.