THE NERVOUS SYSTEM 1489 



The pars intermedia of Wrisberg or sensory portion of the facial 



nerve arises from the central poles of the bipolar cells of the genicu- 

 late ganglion on the facial nerve in the aqueduct of Fallopius. This 

 ganglion resembles the Gasserian ganglion of the fifth nerve and the 

 spinal ganglia, and most of the peripheral poles of its bipolar cells 

 give rise to the chorda tympani nerve. The pars intermedia emerges 

 from the aqueduct of Fallopius into the internal auditory meatus. 

 After issuing from that meatus it passes to the lower border of the 

 pons Varolii, where it hes between the facial nerve proper and the 

 auditor}- nerve. The nerve then enters the medulla oblongata, 

 and passes downwards to the upper part of the nucleus of the 

 fasciculus solitarius (see Glosso-phar^ngeal Xerv^e), and its fibres 

 terminate in arborizations around the cells of the upper part of 

 that nucleus. In this situation it is closely associated with the 

 terminal afferent or sensory fibres of the glosso-phaiymgeal nerve. 



The facial nerve proper emerges from the brain at the lower border 

 of the pons Varolii in front of, and internal to, the auditory nerve ; 

 and the pars intermedia of Wrisberg enters between the facial nerve 

 proper and the auditory nerve. 



Distribution, Motor Part (Facial Nerve Proper). — (i) The muscles 

 of the face, including the buccinator ; (2) the occipito-frontalis ; 

 (3) the muscles of the auricle ; (4) the posterior belly of the digastric 

 and the stylo-hyoid; (5) the platysma myoides; and (6) the stapedius 

 muscle, within the tympanic cavity. 



Sensory Part (Pars Intermedia of Wrisberg and Chorda Tympani). 

 — The anterior two-thirds of the tongue (sense of taste). 



The chorda tympani nerve conveys secretory and vciso-dilator 

 fibres from the facial nerve proper to the submaxillary and sub- 

 lingual salivary glands. 



The lai^e superficial petrosal nerve, from the geniculate ganglion 

 of the facial nerve, is concerned in the supply of the mucous mem- 

 brane of the soft palate, the path being as follows: (i) Large super- 

 ficial petrosal nerve (facial fibres) ; (2) the Vidian nerve; (3) Meckel's 

 ganglion ; and (4) the descending palatine nerves. 



Eighth, Auditory, or Acoustic, Nerve. — The auditory nerve is the 

 nerve of hearing and of equilibrium. It is an afferent or centripetal 

 nerve which conducts impressions from the membranous labvrinth 

 (cochlea and vestibule) to the medulla oblongata and pons Varolii, 

 and thence to the cerebrum and cerebellum. It consists of two 

 divisions — ^namely, the cochlear nerve or root, and the vestibular 

 nerv'e or root. 



The fibres of the cochlear nerve arise from the bipolar cells of the 

 spiral ganghon in the spiral canal of the modiolus, the modiolus 

 being the central pillar of the osseous cochlea. The fibres of the 

 vestibular nerve arise from the bipolar cells of the ganglion of 

 Scarpa at the deep end of the internal auditorv meatus. 



The two nerves or roots reach the brain at the lower border of 

 the pons VaroHi, external to the facial ner\^e.and ventral to the 

 restiform body. They have different central connections, and 



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