Final answer:
The attachment point of the wings to the fuselage in birds is determined by flight muscles and skeletal modifications.
Step-by-step explanation:
The attachment point of the wings to the fuselage is determined by the flight muscles and skeletal modifications in birds. The flight muscles, such as the pectoralis major and supracoracoideus, are attached to the keel of the sternum. This provides the necessary power for the flapping motion of the wings. In addition, birds have a fused clavicle called the furcula or wishbone, which provides support to the shoulder girdle during flight.