FACIAL yERVE—AVDITORY XERVE 765 



inwards on the deoi) surface of tlie zygoniatici and the levator lahii superioris. 

 Under cover of the latter muscle they communicate with the terminal branches of 

 the superior maxillary division of the fifth nerve, formin<i the infraorbital plexus ; 

 thence twigs extend to the nose, and communicate with the nasal hrandi of tln^ 

 o])hthalniic nerve. The infraorlntal hranch also forms communications with other 

 branches of the facial, namely with the malar above and with the Ituccal below. It 

 sui)i)lies the zygomatici, the levator labii superioris, the levator labii sujterioris 

 aliesiue nasi, the levator anguli oris, the pyramidalis nasi, the compressor nasi, and 

 the depressor ala; nasi. It also gives twigs to the buccinator and to the orbicularis 

 oris. 



The CERVICO-FACIAL DIVISION of the facial nerve is directed forwards and 

 downwards through the parotid gland, and, like the temporo-facial division, it 

 crosses on the outer side of the external carotid artery. As it traverses the glandu- 

 lar substance it communicates with the facial branches of the great auricular nerve. 

 As above descril)ed, it terminates in three branches: the buccal, the supra-mandi- 

 bular, and the infra-mandibular. 



(a) The buccal branch is of small size, and is the highest of the three l)ranches 

 of the cervico-facial division. It is placed between the infraorbital and supra- 

 mandibular branches of the facial, and communicates Avith both these branches. 

 It emerges from the parotid gland below Stenson's duct, and crosses the masseter 

 muscle. In front of the anterior border of the masseter, it communicates wdth the 

 long buccal branch of the fifth, and then breaks into twigs, which end in the 

 buccinator and orl)icularis oris. 



{})) The supra-mandibular branch, after escaping from the parotid gland, 

 crosses the loAver part of the masseter muscle, a little way above the angle of the 

 lower jaw, and j^asses forwards, under cover of the risorius and the depressors of 

 the lower lip, as far as the middle line. It communicates with the buccal and 

 infra-mandibular branches of the facial, and with the mental branch of the man- 

 dil)ular nerve. It supplies the risorius, the depressor anguli oris, the depressor 

 labii inferioris, and the levator menti. 



(c) The infra-mandibular branch becomes superficial at the lower margin of 

 the parotid gland, and runs ol)li(piely downwards and forwards, under cover of the 

 )ilatysma, across the side and front of the neck. It forms one or more communi- 

 cating loops, near its commencement, with the great auricular nerA'e, and longer 

 loops, lower down, with the superficial cervical nerve. It supplies the platysma 

 my (tides. 



EIGHTH OR AUDITORY NERVE 



The auditory nerve appears at the lower border of the pons (superficial origin), 

 innnediately external to the facial nerve. It arises by two roots, a lateral and a 

 mesial. These roots embrace the restiform body, the lateral root being extern;d. 

 and the mesial root internal to that body (fig. 450). The lateral root ( su])erficial, 

 dorsal, inferior, or posterior root) is continuous with the cochlear nci-vi-, and is the 

 true nerve of hearing; while the mesial root (deep, ventral, superior, or anterior 

 root) is continued into the vestibular nerve, and is concerned in the maintenance 

 of eciuilibriuni. The mielei in connection with these roots will be first described. 



The small-celled or chief nucleus is superficially placed in the floor of tht> 

 fourtli ventricle. It is largest in the region of the strife medullares, in which 

 situation it appears in coronal sections as a triangular grey mass, which reaches the 

 middle line. It extends forwards from this point as far as the al)ducens nucleus 

 and l)ackwards for about an ecjual distance. Both in front and behind it recedes 

 from the middle line. The nerve-cells forming this nucleus are all of small size. 



The large-celled or Deiters' nucleus is placed close to the inner side of the 

 restiform bodv. It is al)out the same length as the small-celled nucleus, Itut 

 occupies a position deeper and further forwards tlian the latter. The cells of this 

 nucleus are of large size, and are most numerous at the anterior ])art. It degene- 

 rates after destruction of the upper cervical region of the cord or of the lateral lobe 

 of the cerebellum of the same side, therefore it must have close associatiojis with 

 these parts, Init it is probably unconnected with tlie auditory nerve. 



