Which muscle remains unaffected following a complete severance of the cranial portion of the accessory nerve?

Explanation

The stylopharyngeus muscle is not innervated by the cranial part of the accessory nerve; instead, it receives innervation from the glossopharyngeal nerve (cranial nerve IX). Therefore, it remains intact even if the cranial segment of the accessory nerve is completely transected. In contrast, muscles like the cricopharyngeus, palatopharyngeus, and salpingopharyngeus are affected due to their innervation by the cranial accessory fibers.