THE SEVENTH NERVE, OR FACIAL 555 



esses, which are gathered up at the dorsal surface of the nucleus to form a root. 

 The root describes a loop around the nucleus of the sixth nerve, running for- 

 ward for some little distance dorsal to the nucleus, then descending vertically, 

 passing to the outside of its own nucleus, between it and the descending root 

 of the fifth nerve. It emerges at the lower margin of the pons, lateral to the 

 sixth nerve, opposite the front edge of the groove between the olivary and 

 restiform bodies. There are two roots; the lower and smaller is called the 

 pars intermedia, and the upper, pars dura. 



Functions. The seventh nerve is the motor nerve of all the muscles of 

 the face, including the platysma, but not including the muscles of mastication, 

 already enumerated; it supplies, also, the parotid gland, and, through the con- 

 nection of its trunk with the Vidian nerve, some of the muscles of the soft palate. 

 It supplies the stapedius, the lingualis and some other muscles of the tongue, 



pars interned j 



r. auric, vagi 



pet rot . 5 up. 



. motor's]!. 



FIG. 388. Dissection of the Sensory and Motor Divisions of the Facial in a 2o-cm. Embryo 



(Pig). (Streeter.) 



and the posterior part of the digastric and stylo-hyoid. Its branches supply 

 the muscles of the external ear. 



Fibers from the chorda tympani are distributed to the submaxillary gland 

 and produce secretion when stimulated. 



When the facial nerve is divided or in any other way paralyzed, the loss of 

 function in the muscles which it supplies interferes with the perfect exercise 

 of the organs of the special senses. Thus, in paralysis of the facial nerve .the 

 orbicularis palpebrarum being powerless, the eye remains open through the 

 unbalanced action of the levator palpebrae. The conjunctiva is thus contin- 

 ually exposed to the air and dust and is liable to repeated inflammation, which 

 may end in thickening and opacity of the cornea. 



The sense of taste may be weakened or wholly lost in paralysis of the facial 

 nerve, which involves the chorda tympani. This result, which has been ob- 

 served in many instances of disease of the facial nerve in man, appears ex- 

 plicable on the supposition that the chorda tympani is the nerve of taste to the 

 anterior two-thirds of the tongue, its fibers being distributed with the so-called 



