FACIAL NERVE, OR NERVE OF EXPRESSION. 



619 



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 has 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 

 paralysis of the facial nerves upon either side. This single fact is sufficient to show that 

 the main decnssation of the fibres animating the muscles of the face takes place, if at all, 

 at some other point. 



The pathological facts bearing upon the question of decussation of the filaments of 

 origin of the facial have long been recognized. They are, in brief, as follows: When 

 there is a lesion of the brain-substance anterior to the pons Varolii, the phenomena due 

 to paralysis of the facial are observed upon the same side as the hemiplegia, opposite the 

 side of injury to the brain. When the lesion is either in the pons or below it, the face is 



FIG. 201. Superficial branches of the facial and the fifth. (Hirschfeld.) 



1, trunk of the facial ; 2, posterior auricular nerve; 3, branch which it receives from the cervical plexus ; 4, 

 occipital branch; 5, 6, branches to the muscles of the ear; 7, digastric branches; 8, branch to the stylo- 

 hyoid muscle; 9, superior terminal branch; 10, temporal brandies; 11, frontal branches ; 12, branches to 



branches of the cervical nerves. 



affected upon the same side, and not upon the side of the hemiplegia. In view of these 

 facts, the remarkable phenomenon of hemiplegia upon one side and facial paralysis upon 

 the other is regarded as indicating, with tolerable certainty, that the injury to the brain has 

 occurred upon the same side as the facial paralysis, either within or posterior to the pons 

 Varolii. It is unnecessary to enter into a farther discussion of these facts, which are 



