740 THE NERVOUS SYSTEM. 



ganglion on its outer side, between it and the External rectus. Below the optic 

 is the inferior division of the third and the sixth, which lies on the outer side of 

 the orbit. 



Surgical Anatomy. The sixth nerve is more frequently involved in fractures of the base 

 of the skull than any other of the cranial nerves. The result of paralysis of this nerve is internal 

 or convergent squint. When injured so that its function is destroyed, there is, in addition to 

 the paralysis of the External rectus muscle, often a certain amount of contraction of the pupil, 

 because some of the sympathetic fibres to the radiating muscle of the iris pass along with this 

 nerve. 



The Seventh Nerve (Figs. 399, 400, 401). 



The Seventh or Facial Nerve (portio dura) is the motor nerve of all the muscles 

 of expression in the face, and of the Platysma and Buccinator; the muscles of 

 the External ear ; the posterior belly of the Digastric, and the Stylo-hyoid. Its 

 chorda tympani branch is the nerve of taste for the anterior two-thirds of the 

 tongue and the vaso-dilator nerve of the submaxillary and sublingual glands ; its 

 tympanic branch supplies the Stapedius. 



Its superficial origin is from the upper end of the medulla oblongata, in the 

 groove between the olivary and restiform bodies. Its deep origin is from a nucleus 



situated in the reticular formation 

 of the lower part of the pons, a 

 little external and ventral to the 



External pevrosal.- 



5*15^5 ;: T7^s^K\ 1 i*\ this ri s in the fi bres p ui ' sue 



curved course in the substance of 

 the pons. They first pass backward 

 and inward, and then turn upward 

 and forward forming the funiculus 



FIG. 399. The course and connections of the facial nerve i_ r j 



in the temporal bone. teres, which produces an eminence 



(eminentia teres) on the floor of the 



fourth ventricle, and finally bend sharply downward and outward round the upper 

 end of the nucleus of origin of the sixth nerve, to reach their superficial origin 

 between the olivary and restiform bodies. From the nucleus of the third nerve 

 some fibres arise which descend in the posterior longitudinal bundle and join the 

 facial just before it leaves the pons ; these fibres are said to supply the anterior 

 belly of the Occipito-frontalis, Orbicularis palpebrarum, and the Corrugator 

 supercilii, as these muscles have been observed ?o escape paralysis in lesions of the 

 nucleus of the facial nerve. 



The auditory nerve (portio mollis) lies to its outer side ; and between the two 

 is a small fasciculus, the pars intermedia of Wrisberg, which arises from the 

 medulla and joins the facial nerve in the internal auditory meatus. The deep 

 origin of the pars intermedia is from the upper end of the nucleus of the glosso- 

 pharyngeal nerve, and at its emergence it is frequently connected with both nerves. 



The pars intermedia may be regarded as the sensory root of the facial nerve, 

 analogous to the sensory root of the fifth, and its real nucleus of origin would 

 then consist of the geniculate ganglion. 



The facial nerve, firmer, rounder, and smaller than the auditory, passes forward 

 and outward upon the middle peduncle of the cerebellum, and enters the internal 

 auditory meatus with the auditory nerve. Within the meatus the facial nerve lies 

 in a groove along the upper and anterior part of the auditory nerve, and the pars 

 intermedia is placed between the two, and joins the inner angle of the geniculate 

 ganglion. Occasionally a few of its fibres pass into the auditory nerve. Beyond 

 the ganglion its fibres are generally regarded as forming the chorda tympani. 



At the bottom of the meatus, the facial nerve enters the aquseductus Fallopii, 

 and follows the course of that canal through the petrous portion of the temporal 

 bone, from its commencement at the internal meatus, to its termination at the 

 stylo-mastoid foramen. It is at first directed outward between the cochlea and 

 vestibule toward the inner wall of the tympanum ; it then bends suddenly back- 

 ward and arches downward behind the tympanum to the stylo-mastoid foramen. 



