1. The Meningeal branch contains sensory and sympathetic fibers. It enters the skull through the hypoglossal canal, and supplies bone and meninges in the anterior part of the posterior cranial fossa. 2. The descending branch continues as the descendens hypoglossi or the upper root of the ansa cervicalis. 3. Branches are also given to thyrohyoid and geniohyoid muscles. V) CLINICAL CONSIDERARTIONS:1. The XIIth nerve may be damaged by trauma at or below its exit from the skull, e.g. skull fracture, upper cervical fracture or dislocation. The hypoglossal nucleus or its central connections may be involved in intracranial lesions, e.g. haemorrhage, tumors, syringobulbia, multiple sclerosis, infections of the posterior cranial fossa, etc. 2. Peripheral damage to the nerve, or damage to its nucleus, causes a flaccid paralysis of the muscles of the tongue on the affected side, atrophy of the paralysed muscles with ‘wrinkling’ of the tongue on that side, and deviation of the tongue towards the side of the lesion on protrusion. Fasciculation of the affected half of the tongue may also be present.This deviation is due to the unopposed contraction of the contralateral genioglossus, which pulls the base of the tongue forward. Involvement of the hypoglossal nucleus is usually associated with damage to related nerves or medullary structures. 3. Supranuclear damage, e.g. lesions of the corticobulbar tracts, results in a spastic paralysis, without wasting or fibrillation, to the contralateral side of the tongue 4. Hemiparalysis of the tongue may give rise to difficulty with speech, mastication and swallowing.
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