Final answer:
The clavicle is the bone that cannot resist strong forces but provides the only fixed support for the pectoral girdle, essential for the movement and protection of the upper limb.
Step-by-step explanation:
The bone that cannot resist strong forces but provides the only fixed support for the pectoral girdle is the clavicle.
The pectoral girdle consists of two main bones: the clavicle (collarbone) and the scapula (shoulder blade). The clavicle is an S-shaped bone that lies horizontally across the front of the shoulder and attaches to the sternum (breastbone) at one end and the scapula at the other.
Although it may not resist strong forces as well as other bones, the clavicle serves multiple functions. It acts as a strut to hold the scapula and arm laterally away from the thorax, enabling a wide range of motion for the shoulder joint. It also helps to protect the neurovascular bundle that runs to the upper limb. Moreover, the clavicle transfers weight and forces from the arm to the axial skeleton, and thus provides the only fixed point of support for the scapula and the entire upper limb.