Which muscle that positions the pectoral girdle is a large muscle that covers the back and portions of the neck, inserts on the clavicle and scapula, and has varied actions, due to the fact that specific regions can be made to contract independently?

Function. The function of the serratus anterior muscle is to allow the forward rotation of the arm and to pull the scapula forward and around the rib cage. The scapula is able to move laterally due to the serratus anterior muscle, which is vital for the elevation of the arm.

Dialect is probably part of the answer