Final answer:
The nucleus of CN XI (accessory nucleus) is located in the nucleus ambiguus, a brain-stem nucleus that contains neurons associated with the heart.
Step-by-step explanation:
The nucleus of CN XI (accessory nucleus) is located in the nucleus ambiguus. The nucleus ambiguus is a brain-stem nucleus that contains neurons that project through the vagus nerve to terminal ganglia in the thoracic cavity, specifically associated with the heart.
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