Deltoid
Musculus deltoideus
MuscularSuperficial musclesArmLeft and right
View left in 3D View right in 3D
- What it is
- Thick triangular muscle that caps the shoulder. It arises from the lateral third of the clavicle, the acromion and the spine of the scapula, wraps over the head of the humerus and converges on the deltoid tuberosity about 40% of the way down the humerus.
- Function
- Abducts the arm beyond the first ~15° (middle fibres); anterior fibres flex and medially rotate it, posterior fibres extend and laterally rotate it.
- Size
- About 15 cm long, up to 2.5 cm thick over the shoulder.
- Clinical note
- A common intramuscular injection site; its axillary nerve can be damaged in shoulder dislocation or surgical-neck fracture, weakening abduction.