Fig. 6.

Deltoid. The deltoid muscle covers the lateral portion of the shoulder. It is a flat, triangular muscle consisting of three parts: the anterior portion originating from the lateral third of the anterior margin of the clavicle, the middle portion originating from the apex and the lateral margin of the acromion and the posterior portion originating from the lower lip of the spine of the scapula; it is inserted at the level of the deltoid tuberosity of the humerus. US appearance is typical of multipennate muscles with aponeurosis and muscle bundles.