902 NEUROLOGY 





sensory fibers from the middle ear region. A few splanchnic sensory fibers are aho 

 present. 



The motor root arises from a nucleus which lies deeply in the reticular formation 

 of the lower part of the pons. This nucleus is situated above the nucleus ambiguus, 

 behind the superior olivary nucleus, and medial to the spinal tract of the trigemi- 

 nal nerve. From this origin the fibers pursue a curved course in the substance 

 of the pons. They first pass backward and medialward toward the rhomboid 

 fossa, and, reaching the posterior end of the nucleus of the abducent nerve, run 

 upward close to the middle line beneath the colliculus fasciculus. At the anterior 

 end of the nucleus of the abducent nerve they make a second bend, and run down- 

 ward and forward through the pons to their point of emergence between the olive 

 and the inferior peduncle. 



The sensory root arises from the genicular ganglion, which is situated on the genic- 

 ulum of the facial nerve in the facial canal, behind the hiatus of the canal. The cells 

 of this ganglion are unipolar, and the single process divides in a T-shaped manner 

 into central and peripheral branches. The central branches leave the trunk of 

 the facial nerve in the internal acoustic meatus, and form the sensory root; the 

 peripheral branches are continued into the chorda tympani and greater super- 

 ficial petrosal nerves. Entering the brain at the lower border of the pons between 

 the motor root and the acoustic nerve, the fibers of the sensory root pass into the 

 substance of the medulla oblongata and end in the upper part of the terminal 

 nucleus of the glossopharyngeal nerve and in the fasciculus solitarius. 



External superficial petrosal _ 

 Branch to join lesser superficial petrosal 

 Greater superficial petrosal 



Genicular ganglion 



Fia. 789. The course and connections of the facial nerve in the temporal bone. 



From their superficial attachments to the brain, the two roots of the facial nerve 

 pass lateralward and forward with the acoustic nerve to the internal acoustic 

 meatus. In the meatus the motor root lies m a groove on the upper and anterior 

 surface of the acoustic nerve, the sensory root being placed between them. 



At the bottom of the meatus, the facial nerve enters the facial canal, which it 

 traverses to its termination at the stylomastoid foramen. It is at first directed 

 lateralward between the cochlea and vestibule toward the medial wall of the 

 tympanic cavity; it then bends suddenly backward and arches downward behind 

 the tympanic cavity to the stylomastoid foramen. The point where it changes 

 its direction is named the geniculum ; it presents a reddish ganglif orm swelling, the 

 genicular ganglion (ganglion geniculi; geniculate ganglion; nucleus of the sensory root 

 of the nerve) (Fig. 789). On emerging from the stylomastoid foramen, the facial 

 nerve runs forward in the substance of the parotid gland, crosses the external 

 carotid artery, and divides behind the ramus of the mandible into branches, from- 

 which numerous offsets are distributed over the side of the head, face, and upper 

 part of the neck, supplying the superficial muscles in these regions. The branches 

 and their offsets unite to form the parotid plexus. 



Branches of Communication. The branches of communication of the facial nerve 

 may be arranged as follows: 



