Deltoideus

Deltoid muscle
Deltoid muscle
Muscles connecting the upper extremity to the vertebral column
Details
Origin	the anterior border and upper surface of the lateral third of the clavicle, acromion, spine of the scapula
Insertion	deltoid tuberosity of humerus
Artery	thoracoacromial artery, anterior and posterior humeral circumflex artery
Nerve	Axillary nerve
Actions	shoulder abduction, flexion and extension
Antagonist	Latissimus dorsi
Identifiers
Latin	musculus deltoideus
Dorlands /Elsevier	m_22/12548745
TA	A04.6.02.002
FMA	32521
Anatomical terms of muscle []

In human anatomy, the deltoid muscle is the muscle forming the rounded contour of the shoulder. Anatomically, it appears to be made up of three distinct sets of fibers though electromyography suggests that it consists of at least seven groups that can be independently coordinated by the nervous system.

It was previously called the deltoideus (plural deltoidei) and the name is still used by some anatomists. It is called so because it is in the shape of the Greek capital letter delta (Δ). It is also known as the common shoulder muscle, particularly in other animals such as the domestic cat. Deltoid is also further shortened in slang as "delt".

A study of 30 shoulders revealed an average mass of 191.9 grams (6.77 oz) in humans, ranging from 84 grams (3.0 oz) to 366 grams (12.9 oz).

The deltoid originates in three distinct sets of fibers, often referred to as "heads":

Fick divided these three groups of fibers, often referred to as parts (Latin: pars) or bands, into seven functional components: the anterior part has two components (I and II); the lateral one (III); and the posterior four (IV, V, VI, and VII) components. In standard anatomical position (with the upper limb hanging alongside the body), the central components (II, III, and IV) lie lateral to the axis of abduction and therefore contribute to abduction from the start of the movement while the other components (I, V, VI, and VII) then act as adductors. During abduction most of these latter components (except VI and VII which always act as adductors) are displaced laterally and progressively start to abduct.

From this extensive origin the fibers converge toward their insertion on the deltoid tuberosity on the middle of the lateral aspect of the shaft of the humerus; the middle fibers passing vertically, the anterior obliquely backward and laterally, and the posterior obliquely forward and laterally.