THE SEVENTH OR FACIAL NERVE. 815 



inner angle of the orbit with the infratrochlear and nasal branches of the 

 ophthalmic. The deep branches pass beneath the Zygomatici and the Levator labii 

 superioris. supplying them and the Levator anguli oris, and form a plexus (infra- 

 orbital) by joining with the mfra-orbital branch of the superior maxillary nerve 

 and the buccal branches of the cervico-facial. This branch also supplies the 

 Levator labii superioris alaeque nasi and the small muscles of the nose. 



The Cervico-facial division of the facial nerve passes obliquely downward and 

 :V>rward through the parotid gland, crossing the external carotid artery. In this 

 situation it is joined by branches from the great auricular nerve. Opposite the 

 angle of the lower jaw it divides into branches which are distributed on the lower 

 half of the face and upper part of the neck. These may be divided into three sets 

 buccal, supramaxillary, and inframaxillary. 



The buccal branches cross the Masseter muscle. They supply the Buccinator 

 and Orbicularis oris, and join with the infra-orbital branches of the temporo-facial 

 division of the nerve, and with filaments of the buccal branch of the inferior 

 maxillary nerve. 



The supramaxillary or mandibular branches pass forward beneath the Platysma 

 and Depressor anguli oris. supplying the muscles of the lower lip and chin, and 

 communicating with the mental branch of the inferior dental nerve. 



The inframaxiUary or cervical branches run forward beneath the Platysma, 

 and form a series of arches across the side of the neck over the suprahyoid 

 region. One of these branches descends vertically to join with the superficialis 

 colli nerve from the cervical plexus : others supply the Platysma. 



Surgical Anatomy. The facial nerve is more frequently paralyzed than any of the other 

 of the cranial nerves. The paralysis may depend either upon (1) central causes i. e. blood-clots 

 or intracranial tumors pressing on the nerve before its entrance into the internal auditory meat us. 

 It is also one of the nerves involved in " bulbar paralysis." Or (2) it may be paralyzed in its 

 passage through the petrous bone by damage due to middle-ear disease or by fractures of the 

 base. Or (3) it may be affected at or after its exit from the stylo-mastoid foramen. This is 

 commonly known as " Bell's paralysis." It may be due to exposure to cold or to injury of the 

 nerve, either from accidental wounds of the face or during some surgical operation, as removal 

 of parotid tumors, opening of abscesses, or operations on the lower jaw. 



The facial nerve is at fault in cases of so-called "histrionic spasm," which consists in an 

 almost constant and uncontrollable twitching of the muscles of the face. This twitching is 

 sometimes so severe as to cause great discomfort and annoyance to the patient and to interfere 

 with sleep, ami fur its relief the facial nerve has been stretched. The operation is performed 

 by making an incision behind the ear from the root of the mastoid process to the angle of the 

 jaw. The parotid is turned forward, and the dissection carried along the anterior border of the 

 Sterno-mastotd muscle and mastoid process until the upper border of the posterior belly of the 

 Digastric is found. The nerve is parallel to this on about a level of the middle of the mastoid 

 process. When found, the nerve must be stretched by passing a blunt hook beneath it and 

 pulling it forward and outward. Too great force must not be used, for fear of permanent injury 

 to the nerve. 



Eighth Nerve. 



The Eighth or Auditory Nerve (portio mollis) is the special nerve of the sense 

 of hearing, being distributed exclusively to the internal ear. 



Its mperficuU origin is by two roots. One, the mesial, is from the groove 

 between the olivary and restiform bodies at the lower border of the pons. The 

 other, or lateral root, winds around the upper end of the restiform body, dorsally, 

 and joins the former at its exit in the groove. This root is apparently cont?nuous 

 with the auditory striae. The nerve, thus formed, lies external to the facial nerve. 

 Each root has a deep origin : 1. The mesial root is traceable dorsally, through 

 the substance of the medulla, lying close to the mesial or attached surface of the 

 restiform body, to the dorsal auditory nucleus, which lies immediately ventral to 

 a prominence, the acoustic tubercle, on the outer side of the inferior fovea on the 

 floor of the fourth ventricle. 2. The fibres of the lateral root are traceable dor- 

 sally to four different sources: (a) To the accessory or ventral auditory nucleus. 

 which lies close in front of the restiform body and between this root and the 

 mesial ; (6) to its own ganglion, or ganglion of the lateral root, situated among 

 the fibres where they bend around the restiform body ; (c) to the auditory striae ; 



