884 



THE NERVE SYSTEM 



The Facial Nerve Nucleus. The facial nerve proper is to be distinguished from 

 its so-called sensor root, or pars intermedia, or nervus intermedius. 



The axones of the efferent facial nerve arise from cells forming the facial nucleus 

 in the ventrolateral region of the reticular formation, in line with the nucleus 

 ambiguus or nidus pharyngei, a little over 4 mm. (^ inch) from the ventricular 

 floor. These axones converge toward the ventricular floor to form a compact 

 bundle which curves over the abducens nucleus from behind (caudad), overlying 

 it like a horseshoe over a ball (genu facialis internum}; not as a straight but as 

 a bent horseshoe, bent so that its cephalic branch is directed more laterad than 

 its caudal branch. After having encircled the abducens nucleus, the facial 

 root passes ventrolaterad, passing its own nucleus ectad, and emerging in the 

 postpontile groove (recessus facialis). 1 



Pyramidal fibres from the precentral cortex place this nucleus under the in- 

 fluence of the will; it also receives fibres from the trigeminal and acoustic central 

 systems. 



The nervus intermedius is a mixed nerve, containing afferent (taste) fibres and 

 efferent (excitoglandular or secretory) fibres. With respect to its afferent com- 

 ponent it may be regarded as an aberrant portion of the glossopharyngeal nerve. 



Ascending 



Nucleus of cerebellar 

 _ BechterewJibresA Nudeus O f Fibres to 

 Restiform body. ^^^ \ D ei ter s. /raphe. 



Internal Fourth 

 nucleus, ventricle. 



SI t f : f; ,fl' ' I ~^^J 



Descend, root 

 of auditory. 



Accessory 

 nucleus. 



Raphe. 

 Fillet. 



Inf. sensory root 

 of trigeminal. 



Fibres taking 

 oblique course. 

 Pyramidal tract 



FIG. 649. Terminal nuclei of the vestibular root of the auditory nerve, with their upper connections. 



(Schematic.) (Testut.) 



1. Afferent Portion. These axones arise from the cells of the geniculate ganglion, 

 implanted upon the genu facialis externum, and terminate in a nuclear extension ;' 

 cephalad of the nucleus tractus solitarii. They probably convey gustatory sense 

 impulses from the anterior two-thirds of the tongue and the pillars of the soft palate. 



2. Efferent Portion. A nucleus of origin for the excitoglandular elements has 

 been described as a group of cells extending beneath the ventricular floor from 

 the level of the facial nucleus to that of the motor trigeminal nerve, close to the 

 raphe, and called the nucleus salivatorius. 



Peripherally we shall study this nerve as the chorda tympani. The mixed nature 

 of the nervus intermedius and of the geniculate ganglion makes it probable that 

 they combine the elements of a sympathetic and a spinal ganglion; the nerve, at 

 least, contains both vegetative and sensorial elements. 



1 The peculiar course of the deep root of the facial nerve has been shown by Streeter to be due to a 

 pandering of the facial nucleus in the embryonic period. 



