1250 



HI 'MAN ANATOMY. 



Variations. The nerve may be absent on one side, the external rectus being supplied by 

 a branch from the oculomotor. It may have its superficial origin by several widely separated 

 strands, the accessory fasciculi emerging from between the fibres of the pyramid or through 

 the lower border of the pons. 



THE FACIAL NERVE. 



The seventh or facial nerve (n. facialis) is a mixed nerve and consists of two 

 parts, a larger motor and a smaller sensory. The former supplies with motor fibres 

 the muscles of expression, the extrinsic and intrinsic muscles of the external ear, 

 the stylo-hyoid, the posterior belly of the digastric, the platysma myoides and per- 

 haps also the levator palati and the azygos uvulae. Certain of the motor fibres are 

 peculiar and as secretory fibres are destined for the supply of the submaxillary and 

 sublingual glands. The sensory part of the facial conveys gustatory fibres to the 

 anterior two-thirds of the tongue. 



The sensory part is commonly known as the pars intermedia of Wrisberg (n. 

 intermedius) which, instead of being a distinct nerve, may with propriety be regarded 

 as the sensory portion of the seventh a view strongly supported upon morphologi- 

 cal grounds. The sensory fibres are processes of the cells situated within the 



>^ FIG. 1066. 



Brain-stem with nuclei of cranial nerves shown diagrammatically ; motor nuclei and fibres are blue: sensory 

 nuclei and fibres are red. a. oculomotor nerve ; f>, trochlear nerve; c, motor part of trigeminal nerve; rf, sensor 

 part of trigeminal nerve ; f, spinal root of sensory part of trigeminal nerve;/; facial nerve; j?, abduct-ns nerve; i 

 vestibular portion of auditory nerve; ', cochlear portion of auditory nerve; j, glosso-pharyngeal nerve; k, vagu 

 nerve, showing also the nucleus ambiguus in black; /, hypoglossal nerve; m. vagus portion of spinal accessor 

 nerve. (Posty and Spiller.) 



enlargement on the facial nerve known as the geniculate ganglion, which is situate 

 within the facial canal at the so-called knee. Passing through the proximal part 

 of the facial canal, the axones of the geniculate ganglion cells enter the cranium 

 through the internal auditory meatus, lying above the auditory nerve and below 

 the motor root of the seventh, with both of which they communicate. Leaving the 

 meatus, they pass inward and enter the brain-stem at the superficial origin, 

 (Fig. 1046), which is located at the lower border of the pons, between the moto 

 root of the seventh and the auditory nerve. 



Entering tin- substance of tin- medulla, the sensory fibres pass either through ordorsally to 

 the spinal root of the trigeminal nerve to reach the superior part of tin- nucleus of reception, 

 which it shares with the glosSO-pharyngeal and vagus nerves (page 1262). On gaining this 

 nucleus, the sensory tilm-s divide into short ascending and much longer descending branch'- 

 thus behaving in a manner identical with that of the corresponding fibres of the trigeminus an 

 other mixed cranial nerves. The termination of the sensory fibres is around the neuron 

 of tin- reception-nucleus, from which axones pass to the mesial fillet of the opposite side, at* 

 eventually, to the cep-bral cortex. 



n 



