NEUROLOGY 271 



the cerebellum. The nerve then passes ventrally, as does the mo- 

 toris oculi and leaves the brain along the median line. This is a 

 comparatively large nerve and passes somewhat laterally and 

 ventrally from the foramen opticum through a canal in the sphenoid. 

 It then enters the orbital cavity. Some muscular twigs are given 

 off to the quadra tus and to the pyramidalis muscle. This nerve 

 also innervates the external rectus muscle of the eye. The ab- 

 ducens anastomoses with the ramus ciliaris and the ophthalmic nerve 

 and gives fine nerve twigs to the ramus ciliaris externus of the cil- 

 iary ganglion. 



The Facialis and the Acusticus. The facial nerve originates with 

 the auditory (Fig. 62, No. C, 14 and 15) in a very vaguely known 

 manner, from the cerebellum. It divides into three parts. 



The first of these probably comes from the complex ganglion with 

 the posterior roots of the auditory. This part belongs to the somatic 

 sensory group of nerves. From this same group originates the audi- 

 tory, which spreads out into the cochlea and takes the impressions 

 of sound. This nerve is short and thick, and, at the point where it 

 loses its medullary covering on entering the cochlea, there is devel- 

 oped a ganglion. This ganglion is similar to the spinal ganglia. 



The second part is provided with one root which originates mesi- 

 ally and ventrally, from the deeper ganglion cells. Some of the 

 fibers from this root constitute the vestibular branches. They 

 accompany the auditory and supply the anterior part of the ear 

 labyrinth and the semicircular canals. The larger part of the 

 fibers of this trunk make up the intermediate part of the facial. 

 The geniculate ganglion is formed at their fusion. The sympathetic 

 spheno-palatine nerve emerges from this ganglion, coming out of the 

 aqueduct of Fallopius. 



The third part, called the portio dura, is the main facialis. It is 

 located opposite the auditoria intermedia. Its roots may be traced 

 to the complex ganglion, from which they take a direction ventrally 

 from the median portion. 



The facialis, after emerging from the aqueduct of Fallopius, 

 takes a curved course and partly fuses with the sympathetic temporo- 

 lacrimalis on the upper posterior wall of the ear drum. It is here 

 accompanied by the carotid and the cephalic arteries. It leaves 

 the ear drum through an opening in the quadrate bone, giving off a 

 large branch to the digastricus muscle and a small one to the sta- 

 pedius of the columella auris. The facialis trunk is quite large. It 



