THE HEAD AND NECK 1299 



group of fibres as compose the pars intermedia of Wrisberg, which 

 represent the central processes of the unipolar cells of the geniculate 

 ganghon of the facial nerve. In other words, the greater portion 

 of the chorda t^Tupani and the pars intermedia are to be regarded 

 as one nerve, with the imipolar cells of the geniculate ganghon 

 interpolated in their course in the form of ceU-stations. The chorda 

 tjTTipani nerve, however, also contains purely facial fibres, which 

 are the secretory fibres of the submaxillary and sublingual glands. 

 The ners'e is, therefore, a mixed nerve. 



A commumeating branch is given off from the facial nerve, just 

 above the stylo-mastoid foramen, which connects it with the 

 auricular branch (Arnold's nerve) of the pneiunogastric. 



Pars Intermedia of Wrisberg. — The fibres of this small nerve 

 arise from the imipolar ceUs of the geniculate ganghon of the facial, 

 being the central processes of these cells, the peripheral processes 

 representing the principal fibres of origin of the chorda tympani. 

 The pars intermedia is at first closely incorporated with the facial 

 nerve, and passes from the aqueduct of Fallopius into the internal 

 auditory meatus. Here it separates from the facial nerve, and Ues 

 between it and the auditory nerve. After emerging through the 

 orifice of the internal auditory meatus the pars intermedia passes 

 to the lower border of the pons Varolii, where it enters the medulla 

 oblongata, and terminates in the fasciculus solitarius and upper 

 part of the glosso-pharyngeal nucleus. 



The chorda tympani and the pars intermedia of Wrisberg, with 

 the geniculate ganglion interpolated, may be regarded as represent- 

 ing the afferent or sensory root of the facial nerve. 



Geniculate Ganglion. — The geniculate ganghon is situated on the 

 facial nerve in the aqueduct of Fallopius, at the point where the 

 aqueduct, having reached the inner wall of the tympanum, makes 

 a sharp bend before passing backwards. Like a spinal ganghon and 

 the Gasserian ganghon, it consists of unipolar cells, each of which 

 has a central process and a peripheral process. The ganghon is the 

 nucleus of origin of the sensory fibres of the facicd nerve. The 

 central processes of the unipolar cells form the pars intermedia of 

 Wrisberg, and the majority of the peripheral processes form the 

 chorda tympani nerve. Some of the peripheral processes, however, 

 gi\e rise to (i) the great superficial petrosal nerve; (2) the communi- 

 cating branch to the small superficial petrosal nerve; and (3) the 

 external superficial petrosal nerve (inconstant). 



The faciaJ nerve is partly motor and partly sensory. The sensory 

 portion, as stated, is represented by (i) the pars intermedia of Wris- 

 berg; (2) the geniculate ganglion ; and (3) the chorda tympani nerve. 

 The great superficial petrosal nerve is to be regarded as a branch of 

 the sensory portion of the facial nerve. 



Summary of the Petrosal Nerves. — There are three superficial petrosal 

 ner\es, namely, great, small, and external; and there are two deep petrosal 

 aerves, namely, great and smalL 



