FACIAL NERVE IN THE BONE. 



143 



Fig. 35. 



Dissection. The examination of the nerve is to be begun at the stylo- 

 mastoid foramen, and to be carried forwards from that point. AVith this 

 view, the side of the skull should be sawn through vertically between the 

 meatus externus and the anterior border of the mastoid process, so as to 

 open the posterior part of the aqueduct of Fallopius. The nerve will be 

 then seen entering deeply into the substance of the temporal bone ; and it 

 can be followed by cutting away with the bone forceps all the bone pro- 

 jecting above it. In this last step the cavity of the tympanum will be 

 more or less opened, and the chain of bones in it laid bare. 



The nerve is to be traced onwards along the inner side of the tympa- 

 num, till it becomes enlarged, and bends suddenly inwards to the meatus 

 auditorious internus. The surrounding bone is to be removed from that 

 enlargement so as to allow of the petrosal nerves being traced to it ; and 

 the meatus auditorious is to be laid open, to see the facial and auditory 

 nerves in that hollow. 



The course of the chorda tympani nerve (branch of the facial) across 

 the tympanum will be brought into sight by the removal of the central ear 

 bone, the incus. This nerve may be 

 also followed to the facial through 

 the wall of the cavity behind, as well 

 as out of the cavity in front. 



The remaining branches of the 

 facial nerve in the bone are very 

 minute, and are not to be seen ex- 

 cept on a fresh piece of the skull 

 which has been softened in acid. The 

 student may therefore omit the para- 

 graphs marked with an asterisk, till 

 he is able to obtain a part on which 

 a careful examination can be made. 



The facial nerve (fig. 35, *) is re- 

 ceived into the internal auditory mea- 

 tus, and entering the aqueduct of 

 Fallopius at the bottom of that hol- 

 low, is conducted through the tem- 

 poral bone to the stylo-mastoid fora- 

 men and the face (p. 48). In its 

 serpentine course through the bone, 

 the nerve is first directed outwards 

 to the inner wall of the tympanum : 

 at that spot it bends backwards, and 

 is marked by a gangliform swelling 

 (intumuscentia gangliformis), to 

 which several small nerves are united. 

 From this swelling the nerve is con- 

 tinued through the arched aqueduct, to the aperture of exit from the 

 bone. 



The branches of the nerve in the bone serve for the most part to con- 

 nect it with other nerves ; but one supplies the tongue, and another the 

 stapedius muscle. 



* Connecting branches communicate with the auditory and glosso- 

 pharyngeal nerves ; and with two trunks (superior and inferior maxillary) 

 of the fifth nerve. 



NERVES JOINING THE ENLAROI-.MENT OF THK 

 FACIAL NERVE. 



1. Facial nerve. 



2. Large superficial petrosal. 



3. Small superficial petrosal from Jacobson's 



nerve. 



4. External superficial petrosal. 



5. Chorda, tympaui of the facial. 



