What is the deltoid?
The shoulder cap muscle is called the deltoid. Gray's Anatomy (1918) describes it as a thick, triangular muscle that caps the shoulder.
What it is
- A thick, triangular muscle that caps the shoulder.
- Named for its resemblance to the Greek letter delta.
- Its main action is to raise the arm to the side (abduction).
Where it is
- Over the shoulder joint.
- Arises from the clavicle, acromion, and spine of the scapula.
- Inserts halfway down the outer side of the humerus.
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Last verified: 2026-07-18
- Best Anatomy Answers is an educational reference about human anatomy. It is not medical advice — for any health concern, talk to a licensed medical professional.