Muscles Actions, Origins & Insertions Practice Test

From which scapular feature do the deltoid's posterior fibers originate?

Acromion of the scapula Spine of the scapula Clavicle Coracoid process

Correct Answer:

Spine of the scapula

Explanation:

The deltoid has three functional parts, each attaching to a different scapular or clavicular feature. The posterior portion originates from the spine of the scapula, a ridge on the back of the shoulder blade. This location lets the fibers run laterally to insert on the humerus and act to extend and externally rotate the arm. In contrast, the anterior portion attaches to the lateral third of the clavicle (facilitating flexion and medial rotation), and the middle portion attaches to the acromion (primarily facilitating abduction). The coracoid process is not a deltoid origin, as it serves other muscles.

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