443 CRANIAL NERVES. 



Hypoglossal. The twelfth cranial nerve arises from the 

 posterior part of the oblong medulla, in a line with the 

 lower roots of the spinal nerves. It arises from a ganglionic 

 mass in the medulla, is intimately connected with the pos- 

 terior olivary body, and through it with the nerves adja- 

 cent. It passes out of the cranium through a special open- 

 ing at its posterior part, and is entirely distributed to the 

 muscles of the tongue, of which it is the motor nerve. 

 Irritation of its trunk causes convulsive twitching of the 

 tongue, and its section completely paralyses it. It has no 

 sensory fibres at its root, but, like the facial and spinal 

 accessory, acquires some of these from adjacent nerves in 

 its course. It has no connection with the sensibility of the 

 mucous membrane, farther than its power of placing it in 

 a position convenient for the reception of impressions. 



