Final answer:
The left hemisphere of the brain controls right-handed motor functions due to the crossing over of neural pathways at the level of the brainstem.
Step-by-step explanation:
The side of the brain that has control of right-handed motor functions is the left hemisphere. This phenomenon is due to the fact that each hemisphere of the cerebrum controls the opposite side of the body. The left hemisphere is responsible for the motor commands that originate from the precentral gyrus, which control right-sided body movements. Likewise, sensory information is processed by the postcentral gyrus for the opposite side of the body. Since the majority of language functions are localized in the left hemisphere, for most people, right arm movements tied to verbal commands also originate from the left hemisphere.