Final answer:
The correct pairing is 'association fibers // link areas WITHIN a cerebral hemisphere', as they connect different parts of the same cerebral hemisphere. The erector spinae is primarily responsible for extending the vertebral column, and the biceps brachii is the agonist in arm flexion.
Step-by-step explanation:
The correct pairing among the options provided is b. association fibers // link areas WITHIN a cerebral hemisphere. Association fibers are indeed the nerve fibers that connect different parts of the same cerebral hemisphere. The erector spinae is not the prime mover of head flexion but rather the primary extensor of the vertebral column, which includes tasks such as maintaining postural support and allowing the flexibility and rotation of the vertebral column. The adductor magnus muscle is not located in the lateral compartment of the thigh, but in the medial compartment, where it assists in adduction and flexion of the thigh. Lastly, the biceps brachii is the agonist, not the antagonist, during arm flexion; it is the prime mover in this action.