The Vagus nerve is also called the "wanderer" and moves throughout the body to help control the parasympathetic autonomic nervous system. It is always a dull to shiny neutral color and sits along the common carotid arteries in the neck of the animal along the trachea. If you can locate the common carotid arteries you can locate the vagus nerve.

In this picture the shiny white looking thing surrounding the common carotid arteries held up by the probe are the vagus nerve (look close)!
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