Final answer:
An injury to V3 affecting the lateral pterygoid muscle will cause a lesion on the same side of the injury, resulting in atrophy of the same medial pterygoid muscle.
Step-by-step explanation:
The question pertains to the effects of injury to the V3 branch of the trigeminal nerve on the muscles of mastication. Specifically, the lateral pterygoid muscle is innervated by the mandibular nerve (V3), and damage to this nerve would result in issues on the same side as the injury. Therefore, if there is an injury via V3 leading to the dysfunction of the lateral pterygoid muscle, the lesion will be on the same side. The lateral pterygoid is a muscle that moves the mandible from side to side, and along with the medial pterygoid muscle, provides assistance in chewing movements. Atrophy would then occur in the muscle on the side of the lesion, making the correct answer to the question option (c) Same medial pterygoid.