Work in progress...
Another post regarding anatomy here so I will be brief. You see below Posterior, anterior and lateral views of the skeleton. The muscles will be laid starting with a few deep layer muscles outward to the top layer muscles. In lieu of time and space, the number of muscles are limited, but for figure drawing purposes these should get you moving forward.
Shown below; Pectoralis Minor (green): origin; rib 3-5, insertion coracoid process of scapula. Pulls scapula (shoulder) forward toward the anterior chest.
Also shown Sternocleidomastoid (teal): origin; clavicle and manubrium, insertion mastoid process. Pulls skull toward chest also turns skull left or right.
Also shown, Teres Major (blue): Origin; Lowest corner of scapula (inferior angle), insertion; just below head of humerus. Allows for forward rotation of humerus, also aids bringing arm down from raised position.