FACIAL NERVE. 145 



are animated by the motor root of the fifth. This nerve, 

 then, is not only the nerve of mastication, animating all of 

 the -muscles concerned in this act, except two of the most 

 unimportant depressors of the lower jaw (the genio-hyoid 

 and the platysma myoides), but it is concerned indirectly in 

 deglutition. 



Facial Nerve, or Nerve of Expression (the Portio dura of 

 the Seventh). 



The facial, the portio dura of the seventh according to 

 the arrangement of Willis, is one of the most interesting of 

 the cranial nerves. Its anatomical relations are quite intri- 

 cate, and its communications with other nerves, very numer- 

 ous. As far as can be determined by experiments upon 

 living animals, this nerve is exclusively motor at its origin ; 

 but in its course it presents anastomoses with the sympa- 

 thetic, with branches of the. fifth, and with the cervical 

 nerves, undoubtedly receiving sensory filaments. While 

 the chief physiological interest attached to this nerve de- 

 pends upon its action upon muscles, it is important to study 

 its origin, distribution, and communications. 



Physiological Anatomy. The portio dura of the seventh 

 has its apparent origin from the lateral portion of the me- 

 dulla oblongata, in the groove between the olivary and the 

 restiform body, just below the border of the pons Varolii, its 

 trunk being internal to the trunk of the portio mollis, or au- 

 ditory nerve. It is separated from the auditory by the two 

 filaments constituting what is known as the intermediary 

 nerve of Wrisberg, or the portio inter duram et mollem. 

 As this little nerve joins the facial, it must be included in 

 its root. It is called the accessory root by Sappey. 1 



There are certain pathological considerations which ren- 

 der the deep, or real origin of the facial a question of the 



1 SAPPEY, Traite d'anatomie descriptive, Paris, 1852, tome ii., p. 251. 



