THE FACIAL NERVE. 



251 



VII. FACIAL NERVE. 



The nucleus of the seventh or facial nerve is situated in the formatio reticularis 

 of the lower part of the pons, about on the same level as the nucleus of the sixth 

 nerve, but farther from the floor of the fourth ventricle. The fibres leave the back 

 of the nucleus, and are directed at first dorso-mesially towards the lower end of the 



Fig. 167. PLAN OF THE ORIGINS OP THE SIXTH AND SEVENTH 

 CRANIAL NERVES. (Adapted from Schwalbe. ) 



The outline represents a transverse section of the lower 

 part of the pons, on to which the course of the facial nerve is 

 projected : VI, sixth nerve ; N.VI, its nucleus ; VII, facial 

 nerve ; VII. A, the ascending portion of its root, supposed to be 

 seen in optical section : N.VII, its nucleus ; SO, superior 

 olive ; A.V, ascending or bul bar root of fifth nerve ; VIII. M, 

 mesial root of auditory nerve. 



abducent nucleus. Here they are collected into a 



well-marked bundle, which ascends for a short 



distance close beneath the floor of the ventricle, 



then bends sharply downwards and outwards over 



the upper end of the abducent nucleus (inner genu 



of ihe facial nerve], and finally runs forwards and 



outwards through the lower part of the pons, to 



emerge at the upper end of the medulla oblongata in the depression between^ the 



olivary and restiform bodies. Those fibres of the nerve, however, which supply 



the frontalis, orbicularis palpebrarum and corrugator supercilii muscles (ocular 



facial) probably arise from the oculomotor nucleus, and descend by the posterior 



Fig. 168. THE FACIAL NERVE IN ITS CANAL, 



WITH ITS CONNECTING BRANCHES, &C. 



(From Sappey, after Hirschfeld and Le- 



veille.) | 



The mastoid and a part of the petrous bone 

 have been divided nearly vertically, and the 

 canal of the facial nerve opened in its whole 

 extent from the internal meatus to the stylo- 

 mastoid foramen ; the Vidian canal has also been 

 opened from the outer side : 1, facial nerve in 

 the first horizontal part of its course ; 2, its 

 second part turning backwards ; 3, its vertical 

 portion ; 4, the nerve at its exit from the stylo- 

 ma'stoid foramen ; 5, geniculate ganglion ; 6, 

 large superficial petrosal nerve ; 7, spheno- 

 palatine ganglion ; 8, small superficial petrosal 

 nerve ; 9, chorda tympani ; 10, posterior auricu- 

 lar branch cut short ; 11, branch to the digastric 

 muscle ; 12, branch to the stylo-hyoid muscle ; 

 13, twig uniting with the glosso-pharyngeal nerve (14 and 15) 



longitudinal bundle to join the issuing portion of the root ; and it is possible that 

 the fibres for the orbicularis oris are derived from the hypoglossal nucleus. 



At its superficial origin the facial nerve rests against, and commonly adheres for 

 a short distance to, the lower border of the pons just where the latter is passing into 

 the middle peduncle of the cerebellum, and immediately below the fifth nerve. To 

 its outer side is the auditory nerve, and between the two is a slender fasciculus 

 (fig. 140, between vn and Vin) known as the pars or portio intermedia of 

 Wrisberg (n. intermedius), which joins the facial nerve in the auditory canal. 



