Final answer:
The serratus anterior, pectoralis minor, and subclavius muscles are the main muscles responsible for protraction of the scapulothoracic joint. They work by moving the scapula forward around the rib cage, with the serratus anterior playing a particularly central role.
Step-by-step explanation:
The muscles responsible for protraction of the scapulothoracic (ST) joint are mainly the serratus anterior, pectoralis minor, and subclavius. These muscles are located on the anterior thorax and work by moving the shoulder blade (scapula) forward and around the rib cage. Specifically, the serratus anterior, with its multiple attachments along the ribs, plays a key role in protracting as well as stabilizing the scapula during this movement. It functions in pushing actions and is crucial in movements such as reaching or thrusting the arm. On the other hand, the pectoralis minor aids in this motion by drawing the scapula anteroinferiorly towards the thoracic wall, and the subclavius stabilizes the clavicle during scapular protraction.
When considering the final answer in two line explanation in 300 words, it's clear that protraction of the scapulothoracic joint is facilitated primarily by the anterior thoracic muscles, especially the serratus anterior, with the pectoralis minor and subclavius also contributing to this movement. These muscles work collectively to move the scapula forward and accommodate various arm movements.