FACIAL, OR NERVE OF EXPRESSION 505 



opening is adapted to the size of the alimentary bolus. These muscles 

 are animated by the motor root of the fifth. This nerve, then, is not 

 only the nerve of mastication, animating all 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 indi- 

 rectly in deglutition. 



FACIAL, OR NERVE OF EXPRESSION (SEVENTH NERVE) 



The anatomical relations of the facial nerve are quite intricate and it 

 communicates freely with other nerves. So far as can be determined 

 by experiments on living animals, this nerve is exclusively motor at 

 its origin ; but in its course it presents anastomoses with the sympathetic, 

 and with branches of the fifth and the cervical nerves, receiving sensory 

 filaments. 



Physiological Anatomy. The facial nerve has its apparent origin 

 from the lateral portion of the medulla oblongata, or bulb, in the groove 

 between the olivary and restiform bodies just below the border of the pons 

 Varolii, its trunk being internal to the trunk of the auditory nerve. It 

 is separated from the auditory by 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 usually is included in 

 its root. 



Anatomists have endeavored to trace the fibres of the facial from 

 their point of emergence from the encephalon to their true origin, but 

 with results not entirely satisfactory. Its fibres pass inward, with one 

 or two deviations from a straight course, to the floor of the fourth 

 ventricle, where they spread out and become fan-shaped. In the 

 floor of the fourth ventricle certain of the fibres have been thought to 

 terminate in the cells of the gray substance, and others have been traced 

 to the median line, where they decussate ; but the course of many of the 

 fibres has not been satisfactorily established. The fibres of origin of 

 the intermediary nerve of Wrisberg have been traced to the nucleus 

 of the glosso-pharyngeal. 



It is evident from physiological experiments that the decussation of 

 the fibres in the floor of the fourth ventricle itself is not very important. 

 Vulpian made, in dogs and rabbits, a longitudinal section in the middle 

 line of the ventricle, which would necessarily have divided the fibres 

 passing from one side to the other, without producing notable paraly- 

 sis of the facial nerves on either side. This observation shows that the 

 main decussation of the fibres animating the muscles of the face takes 

 place in some other situation. 



