THE SEVENTH OR FACIAL NERVE 997 



In the sphenoidal fissure (Fig. 738) the trochlear nerve and the frontal and 

 lacrimal branches of the ophthalmic division of the trigeminal lie upon the same 

 plane, the former being most internal, the latter external, and they enter the cavity 

 of the orbit above the muscles. The remaining nerves enter the orbit between 

 the two heads of the External rectus muscle. The superior division of the 

 oculomotor nerve is the highest of these; beneath this lies the nasal branch of 

 the ophthalmic nerve; then the inferior division of the oculomotor nerve; and 

 the abducent nerve lowest of all. 



In the orbit (Figs. 729 and 733) the trochlear nerve and the frontal and lacrimal 

 divisions of the ophthalmic nerve lie on the same plane immediately beneath the 

 periosteum, the trochlear nerve being internal and resting on the Superior oblique 

 muscle, the frontal nerve resting on the Levator palpebrae muscle, and the lacrimal 

 nerve on the External rectus muscle. Next in order comes the superior division 

 of the oculomotor nerve, lying immediately beneath the Superior rectus muscle, 

 and then the nasal branch of the ophthalmic nerve, 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 ciliary ganglion 

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

 nerve is the inferior division of the oculomotor nerve and the abducent nerve, 

 which lie on the outer side of the orbit. 



Applied Anatomy. It is often stated that the abducent nerve is more frequently involved in 

 fractures of the base of the skull than any other of the cranial nerves. As a matter of fact, however, 

 it is injured in only about 2 per cent, of cases of fracture of the skull (Putscher). Cases have been 

 reported in which the nerve was actually severed. The nerve may be injured by traction, 

 pressure of a blood clot, of a tumor, or of an arteriovenous aneurism. 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 contrac- 

 tion of the pupil, because some of the sympathetic fibres to the radiating muscle of the iris pass 

 along with this nerve. 



THE SEVENTH OR FACIAL NERVE (N. FACIALIS) (Figs. 739, 740). 



The seventh or facial nerve is the motor nerve of all the, muscles^of expression 

 in thejace, and of the Platvsma and Buccinator; the muscles of the external ear, 

 the posterior belly of the Digas- 

 tric, and the Stylohyoid. The 

 chorda tympani (or nervus inter- 

 medius) is referred to as the sen- 



SOr portion of the facial. Intumescentia ganglioformis 



Its superficial origin is from the 

 upper end of the medulla oblon- 

 gata, in the groove between the 



nliVo r. r>r\ rocfifrT-m K/~>/^T7 o ^7/, FlG - 739 - The course and connection of the facial nerve 



ill " nd rc^to_mi bOgy. lts dee P in the temporal bone. 



origin is from a nucleus situated in 



the floqrjof the fourth. ventricle, beneath the superior fovea (Fig. 648). The facial 

 nucleus is deeply placed in the reticular formation of the lower part of the pars 

 dorsalis pontis, a little external and ventral to the nucleus of the abducent nerve. 

 From this origin the fibres pursue a curved course in the substance of the pars 

 dorsalis pontis. They first pass backward and inward, and then turn upward 

 and forward, forming the genu internum, which with the nucleus abducentis 

 produces an eminence, the eminentia teres or abducentis, on the floor of the fourth 

 ventricle, and finally bend sharply downward and outward around the upper end 

 of the nucleus of origin of the abducent nerve, to reach their superficial origin 

 between the olive and restiform body. From the nucleus of the oculomotor 



