256 THE CRANIAL NERVES. 



CERVICO-FACIAL DIVISION. This division of the facial nerve is directed obliquely 

 through the parotid gland towards the angle of the lower jaw, and gives branches to 

 the face below those of the preceding division, and to the upper part of the neck. 

 The branches are named buccal, mandibular, and cervical. In the gland, this divi- 

 sion of the facial nerve is joined by filaments of the great auricular nerve of the 

 cervical plexus, and offsets from it penetrate the substance of the gland. 



The buccal branches (inferior bucco-labial) are directed across the masseter 

 muscle to the angle of the mouth ; supplying the buccinator and sphincter muscles, 

 they communicate with the temporo-facial division, and on the buccinator muscle 

 join with filaments of the buccal branch of the inferior maxillary nerve. 



The mandibular branch (supramaxillary), sometimes double, runs forwards 

 beneath the depressor anguli or is, and, after communicating with the mental branch 

 of the inferior dental nerve, supplies the muscles of the lower lip. One superficial 

 branch is continued along the margin of the lower jaw to the chin. 



The cervical branch (inframaxillary) perforates the deep cervical fascia and 

 divides into slender offsets, which form arches beneath the platysma as low as the 

 hyoid bone. They supply the platysma, and form one or two loops of communica- 

 tion with the upper division of the superficial cervical nerve. 



SUMMARY. The facial nerve is the principal motor nerve of the head, supplying 

 all the superficial, and some of the deep muscles. Its superficial offsets are distri- 

 buted to the muscles of the scalp, the muscles of the external ear, nose, mouth, and 

 eyelids (with the exception of the levator palpebrae superioris), and to the cutaneous 

 muscle of the neck (platysma). Of the deep muscles, it supplies the stapedius, stylo- 

 hyoid, and posterior belly of the digastric (according to some also the levator palati 

 and azygos uvulas muscles through the large superficial petrosal nerve). It also 

 furnishes, through the chorda tympani, secretory and vaso-dilator fibres for the 

 submaxillary and sublingual glands ; and the same nerve would appear to contain 

 the taste-fibres from the fore part of the tongue. 



The facial nerve is freely connected with the three divisions of the fifth nerve ; 

 and it also has communications with the spheno-palatine, submaxillary and otic 

 ganglia, with the auditory, glosso-pharyngeal and pneumo-gastric nerves (through 

 the auricular branch of the latter), and with parts of the sympathetic and spinal 

 nerves. 



Filaments which may be traced from the branches of the facial nerve to the skin 

 of the face and neck are doubtless derived from the communications with sensory 

 nerves, especially the auriculo-temporal, great auricular and superficial cervical. 



VIII. AUDITORY NERVE. 



The eighth or auditory nerve (n. acusticus) makes its appearance on the outer side 

 of the facial nerve, and is closely adherent for a short distance to the lower border 

 of the middle peduncle of the cerebellum. It begins by two roots, the one of which, 

 the mesial or anterior (radix vestibularis], passes obliquely backwards on the inner 

 side of the restiform body to the dorsal auditory nucleus in the floor of the fourth 

 ventricle, while the other, the lateral or posterior (radix cochlearis), passes round the 

 outer side of the restiform body, where it is somewhat enlarged and contains 

 numerous nerve-cells (ganglion of the lateral root, ganglion radicis cochlearis), and 

 appears to be continued into the striae medullares. 



The fibres of the auditory nerve, both central and peripheral, have their origin 

 in the cells of the several portions of the acoustic ganglion (vestibular ganglion, 

 spiral ganglion of the cochlea, and perhaps also the ganglion of the lateral root), 

 which is the equivalent of an intervertebral ganglion ; and the auditory nerve in 

 the meatus corresponds therefore to the posterior root of a spinal nerve. The 



