Deltoid

Proximal Attachment: Lateral third of clavicle; acromion and spine of scapula

Distal Attachment: Deltoid tuberosity of humerus

Innervation: Axillary nerve (C₅, C₆)

Main Action(s):

Clavicular (anterior) part - Flexes and medially rotates arm

Acromial (middle) part - Abducts arm

Spinal (posterior) part - Extends and laterally rotates arm