The Hypoglossal Nerve (XII)

The hypoglossal nerve is motor to the intrinsic and extrinsic muscles of the tongue, which are derived from the myotomes of occipital somites. After leaving the ventral aspect of the medulla oblongata (see Fig. 8.19), the nerve passes through the hypoglossal canal before crossing the nerves of the vagus group to continue toward the tongue, which it enters ventral to the glossopharyngeal nerve. It ramifies within the tongue substance to reach the various muscles.

A destructive lesion of this nerve paralyzes the ipsilateral muscles, allowing a deviation of the tongue toward the normal side. A marked atrophy of the denervated side eventually develops.