Hi,

The Deltoid muscle is the main muscle of the shoulder. It consists of three muscle heads: the anterior deltoid, lateral deltoid, and posterior deltoid. All assist with arm elevation during a process called glenohumeral elevation and play a large role in the movement and overall stability of the shoulder joint and upper arm. The entire deltoid muscle spans from the spine of the scapula to the lateral portion of the clavicle.

Motor function which the deltoid is responsible for includes shoulder abduction, shoulder flexion, and shoulder extension (which allows the shoulder to stay at its resting position while also giving the option of backward movement).

Hello
The deltoid muscle is a rounded, triangular muscle located on the uppermost part of the arm and the top of the shoulder. It is named after the Greek letter delta, which is shaped like an equilateral triangle.
The deltoid is widest at the top of the shoulder and narrows to its apex as it travels down the arm. Contraction of the deltoid muscle results in a wide range of movement of the arm at the shoulder due to its location and the wide separation of its muscle fibers.
Hope it helps

The deltoid is a thick, triangular shoulder muscle . It gets its name because of its similar shape to the Greek letter ‘delta’. The muscle  has a wide origin spanning the clavicle , acromion and spine of scapula . It passes inferiorly surrounding the glenohumeral joint  on all sides and inserts onto the humerus  .

The deltoid is formed of acromial, clavicular and scapular spinal parts. Acromial part (middle fibres) abducts  the arm  , while the clavicular and scapular spinal parts play a significant role in stabilization, ensuring a steady plane of abduction. Additionally, the clavicular part (anterior fibers) can act as a flexor and internal rotator of the arm, while the scapular spinal part (posterior fibers) can extend and externally rotate the arm.