THE SEVENTH OR FACIAL NERVE. 811 



In the orbit the fourth and the frontal and lachrymal divisions of the ophthal- 

 mic lie on the same plane immediately beneath the periosteum, the fourth nerve 

 being internal and resting on the Superior oblique, the frontal resting on the 

 Levator palpebne. and the lachrymal on the External re*ctus. Next in order 

 comes the superior division of the third nerve, lying immediately beneath the 

 Superior rectus, and then the nasal branch of the ophthalmic, crossing the optic 

 nerve from the outer to the inner side of the orbit. Beneath these is found the 

 optic nerve, surrounded in front by the ciliary nerves, and having the lenticular 

 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. 



Seventh Nerve (Figs. 487 and 489). * (VHVVVUAANA^C^ tf 



" " " ~\ 



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

 cles 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. Through its chorda tym- Elienial petrosal _ 



pani it supplies the Lingualis; by *-J jgg 8tt2=SJjg^ 



its tvmpanic branch the btapedms. 



T. * / 7 f A u Intumescentia ganglicformu. 



Its superficial origin is trom the 



upper end of the medulla oblon- 



gata. in the groove between the Seventh pair { 



olivary and restiform bodies. Its 



h-ep origin is from a nucleus in the 



pons, below the floor of the fourth 



ventricle, somewhat ventral and external to the nucleus of the sixth nerve. 



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

 is a small fasciculus (portio inter duram et mollem of Wrisberg, or pars intermedia), 

 which arises from the medulla and joins the facial nerve in the internal auditory 

 meatus. At its origin it is frequently connected with both the nerves between 

 which it lies. 



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

 forward and outward together with that nerve, and with it enters the internal 

 auditory meatus. Within the meatus the facial nerve lies in a groove along 

 the upper and anterior part of the auditory nerve. The pars intermedia 

 is placed between the facial and auditory nerves in the internal auditory 

 meatus ; a few of its fibres frequently pass into the auditory nerve, while 

 the remainder join the facial. At the bottom of the meatus it is connected to this 

 nerve by one or two slender filaments. 



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

 and follows the serpentine 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 toward the inner 

 wall of the tympanum, where it forms a reddish gangliform swelling (intumescentia 

 ganglioformis, or geniculate ganglion), and is joined by several nerves ; then bending 

 suddenly , backward, it runs in the internal wall of the tympanum, above the 

 fenestra ovalis. and at the back of that cavity passes vertically downward behind 

 the tympanum to the stylo-mastoid foramen. On emerging from this aperture it 

 runs forward in the substance of the parotid gland, crosses the external carotid 

 artery, and divides behind the ramus of the lower jaw into two primary branches. 

 temporo-facial and cervico-facial, from which numerous offsets are distributed over 



