Final answer:
The pectoral girdle, consisting of the clavicle and scapula, along with associated muscles, connects the arms to the body and enables shoulder positioning and arm movement.
Step-by-step explanation:
The structures that connect the arms to the body, position the shoulders, and provide a base for arm movement are the bones and muscles of the pectoral girdle. The pectoral girdle consists of the clavicle (collarbone) and the scapula (shoulder blade), which work together with the humerus (arm bone) to form the shoulder joint. Muscles that position the pectoral girdle and facilitate arm movement include the subclavius, pectoralis minor, and serratus anterior on the anterior thorax, and the trapezius, rhomboid major and rhomboid minor on the posterior thorax.
The clavicle serves as a strut, supporting the scapula and holding the shoulder joint superiorly and laterally from the body which allows for a wide range of motion. The clavicle also transmits forces from the upper limb to the sternum and axial skeleton and protects underlying nerves and blood vessels. The scapula articulates with the humerus, and together with the muscles that move the humerus such as the pectoralis major and the latissimus dorsi, it enables various arm movements.