Final answer:
The scapula's lack of direct skeletal attachment and support from the mobile clavicle joint allow for a significant range of movement in the shoulder, enabling independent mobility of each pectoral girdle and facilitating a variety of arm and shoulder actions.
Step-by-step explanation:
The scapula, or shoulder blade, has no direct attachment to the axial skeleton, which allows for a wide range of motion in the shoulder area. Since the right and left pectoral girdles are not joined, they can operate independently. This structure is mainly supported and facilitated by the clavicle, which connects to the axial skeleton via a single, highly mobile joint.
The clavicle also contributes to the movement of the shoulder by serving as a strut between the shoulder blade and the sternum, hence transmitting weight and forces from the upper limb to the trunk. Additionally, muscles play a critical role in connecting the scapula to the rest of the skeleton, allowing movements such as superior rotation, which is vital for tasks like arm abduction beyond shoulder height and carrying heavy loads.
The mobility of the scapula is essential for the extensive range of movements performed by the shoulder and upper limb, which includes actions like reaching, lifting, and carrying.