Complex sentence: Like all muscles of facial expression, the zygomatic major is innervated by the facial nerve (the seventh cranial nerve), more specifically, the buccal and zygomatic branches of the facial nerve.
Split into simpler sentences: Like all muscles of facial expression, the zygomatic major is innervated by the facial nerve (Cranial Nerve VII). More specifically the buccal and zygomatic branches of the facial nerve.