138 NERVOUS SYSTEM. 



I 



What is the origin of the facial or seventh nerve ? 



It arises in the floor of the fourth ventricle, and its fibres emerge 

 at the edge of the pons Varolii in company with the (eighth) 

 auditory nerve (sometimes known as the portio mollis ; the facial 

 being then called the portio dura of the seventh pair, when the 

 classification of the cranial nerves is made into nine pairs). It 

 passes into the internal auditory canal, and escapes from the 

 skull by way of the aqueduct of Fallopius and the stylo-mastoid 

 foramen. 



How is the facial nerve distributed? 



It is almost wholly a motor nerve, and is distributed to all of the 

 muscles of the face (Fig. 39) except those mentioned as controlled 

 by the motor branch of the trigeminus nerve. The muscles of the 

 eyelids and the muscles of the palate in part are innervated by it, 

 as well as the parotid and submaxillary glands, through the chorda 

 tympani. In the neck it supplies the posterior belly of the digas- 

 tric and the platysma myoides muscles. It also sends branches to 

 the stapedius muscle of the internal ear and to all of the muscles 

 of the external ear. The branches passing to the salivary glands 

 are secretory in their function; and this is the only exception to 

 the motor influence of the nerve. 



What is the function of the facial nerve ? 



It is the motor nerve which parallels in its distribution the 

 sensory root of the fifth ; it supplies the superficial muscles, as the 

 latter does the skin. It is the nerve of expression, by which the 

 features are made to reflect the emotions. 



What is the effect of paralysis of this nerve ? 



If the nerve be divided or diseased, the face of that side is 

 devoid of motion (Fig. 40), and becomes smooth and expression- 

 less, while the sound side is held in its customary pose. The 

 eyelids cannot close themselves, and the lips do not oppose properly, 

 on account of the defective action of the orbicular muscle. There 

 is difficulty in drinking and in articulation for the same reason. 



State what influence is ascribed to the chorda tympani branch. 

 The chorda tympani is a small filament given off .from the facial 

 in the aqueduct of Fallopius, some of whose fibres are distributed to 

 the submaxillary gland. If this nerve be divided, the secretion of 

 saliva from the gland is greatly diminished, while stimulation of the 



