Delt - Human Anatomy - Origins

Origins

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

• The anterior or clavicular fibers arises from most of the anterior border and upper surface of the lateral third of the clavicle. The anterior origin lies adjacent to the lateral fibers of the pectoralis major muscle as do the end tendons of both muscles. These muscle fibers are closely related and only a small chiasmatic space, through which the cephalic vein passes, prevents the two muscles from forming a continuous muscle mass.

• The anterior deltoid are commonly called front delts for short.

• Lateral or acromial fibers arise from the superior surface of the acromion process.

• They are commonly called lateral deltoid. This muscle is also called middle delts, outer delts, or side delts for short.
• They are also mistakenly called medial deltoid, which is wrong, as their origin is the least medial portion of the deltoid.

• Posterior or spinal fibers arise from the lower lip of the posterior border of the spine of the scapula.

• They are commonly called posterior deltoid or rear deltoid (rear delts for short ).

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.

Front. Back. Animation. Deltoid muscle. Anterior part of deltoid (arises from most of the anterior border and upper surface of the lateral third of the clavicle.) Lateral part of deltoid (arises from the superior surface of the acromion process.) Posterior part of deltoid (arises from the lower lip of the posterior border of the spine of the scapula.)