THE SEVENTH NERVE, OR FACIAL 657 



through the reticular formation, to the surface, which it reaches at the lower 

 edge of the pons, opposite the front end of the pyramid. 



Functions. The sixth nerve is exclusively motor, and supplies only the 

 rectus externus muscle of the eye. The muscle is paralyzed when the nerve 

 is divided. In all such cases of paralysis the eye squints inward and cannot 

 be moved outward. 



The Seventh Nerve, or Facial. Origin. The facial or seventh pair of 

 nerves arises from the floor of the central part of the fourth ventricle, behind 

 and in line with the motor nucleus of the fifth, to the outside of and deeper 

 down than the nucleus of the sixth. The nucleus is narrower in front than 

 behind, and consists of large motor cells with well-marked axis-cylinder proc- 

 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 forward for some little distance dorsal to the nucleus, then descend- 

 ing vertically, passing to the outside of its own nucleus, between it and the 



pars intermed -j 



r. auric. 



i 

 petros . sup. maj. 



L motor ET. 



FIG. 413. Dissection of the Sensory and Motor Divisions of the Facial in a ao-cm. Embryo 



(Pig). (Streeter.) 



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. The second or sensory root is smaller and 

 is called the pars intermedia, figure 412. It is the portion which is connected 

 with the chorda tympani and geniculate ganglion, figure 413. The pars 

 intermedia terminates within the brain in the fasciculus solitarius in com- 

 mon with the glosso-pharyngeal. 



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. 

 It supplies the stapedius, the stylo-hyoid and the posterior part of the 

 digastric. Its branches also supply the rudimentary 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 



42 



