STIMULATION OF THE FACIAL. 603 



the sensibility to sounds being increased (oxyakoia, hyperakusis willisiana). The paralysis of 

 the stapedius muscle makes the stapes loose in the fenestra ovalis, so that all impulses from the 

 tympanum act vigorously upon the stapes, which consequently excites considerable vibrations in 

 the fluid of the inner ear. More rarely, in paralysis of the stapedius, it has been observed that 

 low notes are heard at a greater distance than on the sound side (Lucae, Movj). 6. As the 

 facial in man appears to contain fibres for the secretion of sweat, this explains the loss of the 

 power of sweating in the face when the nerve begins to atrophy (Strauss, Block). 



Section of the facial in young animals causes atrophy of the corresponding muscles. The 

 facial bones are also imperfectly developed ; they remain smaller, and hence the bones of the 

 sound side of the face grow towards, and ultimately across, the middle line towards the affected 

 side (Brown- Sequard). The salivary glands also remain smaller. 



Stimulation or irritation in the area of the facial causes partial or extensive, either direct 

 or reflex, tonic or clonic spasms. The extensive forms are known as " mimetic facial spasm." 

 Amongst the partial forms are tonic contraction of the eyelid (blepharospasm), which is most 

 common ; and is caused reflexly by stimulation of the sensory nerves of the eye, e.g., in scrofulous 

 ophthalmia, or from excessive sensibility of the retina (photophobia). More rarely, the excite- 

 ment proceeds from some more distant part, e.g., in one cause recorded by v. Grafe, from 

 inflammatory stimulation of the anterior palatine arch. The centre for the reflex is the facial 

 nucleus. The clonic form of spasm spasmodic ivinlcing (spasmus nictitans) is usually of 

 reflex origin, due to irritation of the eye, the dental nerves, or even of more distant nerves. 

 In severe cases, the affection may be bilateral, and the spasms may extend to the muscles of 

 the neck, trunk, and upper extremities. Contraction of the muscles of the lip may be excited 

 by emotions (rage, grief), or reflexly. Fibrillar contractions occur after section of the facial as 

 a " degeneration -phenomenon " (p. 476). [If the facial be torn out at the stylomastoid 

 foramen, there is paralytic oscillation of the lip muscles (Schiff). If, in such an animal, the 

 posterior root of the annulus of Vieussens be stimulated electrically, as it contains vaso-dilator 

 fibres (Dastre and Morat), not only do the blood-vessels of the cheek and lips dilate, but the 

 veins pulsate and florid blood escapes from the veins, just as occurs in the sub-maxillary gland 

 when the chorda is stimulated. On stimulating the ansa, after section of the seventh, there is 

 a pseudo-motor effect on the muscles of the cheek and lips, so that there is an analogy between 

 the chorda and the ansa (Bogowicz).] Intracranial stimulation of the most varied description 

 may cause spasms. Lastly, facial spasm may be part of a general spasmodic condition, as in 

 epilepsy, chorea, hysteria, tetanus. Aretaeus (81 A.D.) made the interesting observation that 

 the muscles of the ear contracted during tetanus. Very rarely have spasmodic elevation of the 

 palate and increased salivation been described as the result of irritation of the facial (Leube). 

 Moos observed a profuse secretion of saliva on stimulating the chorda during an operation on 

 the tympanic cavity. 



350. VIII. NERVUS ACUSTICUS. Arises by two roots (Stieda) ; a larger anterior and a 

 smaller posterior one. From the former proceeds the vestibular nerve, and from the latter the 

 cochlear nerve; these are separated in the sheep and horse (HorbaczewsTci). Each root springs 

 from a median and a lateral nucleus, so that there are four nuclei. Some fibres come from the 

 cerebellum, and these may be connected with equilibration. The chief mass of the posterior 

 ganglion fibres of the cochlear nerve cross and pass to the corpora quadrigemina, the internal 

 geniculate, and finally to the temporo-sphenoidal lobe ( 378, IV., 2). After extirpation of the 

 temporo-sphenoidal lobe, these fibres atrophy into the internal capsule and internal geniculate 

 body (v. Monakow). The striee acusticse form a second decussating projection system. The 

 origin of both acoustic nerves are connected by commissures in the brain (Flechsig). 



In the course of the internal auditory meatus, the auditory and portio intermedia of the facial 

 exchange fibres, but the physiological significance of this is unknown. 



Function. The acusticus or auditory nerve has a double function : 1. It is 

 the nerve of hearing ; when stimulated, either at its origin, in its course, or at its 

 peripheral terminations, it gives rise to sensations of sound. Every injury, accord- 

 ing to its intensity and extent, causes hardness of hearing or even deafness. 



2. Quite distinct from the foregoing is the other function, which depends upon 

 the semicircular canals, viz., that stimulation of the peripheral expansions in the 

 ampullae influences the movements necessary for maintaining the equilibrium of 

 the body. 



Brenner's Formula. The relation of the auditory nerve to the galvanic current is very 

 important. In healthy persons, when there is closure at the cathode, there is the sensation of 

 a clang (or tone) in the ear, which continues with variations while the current is closed. When 

 the anode is opened, there is a feebler tone (Brenner's Normal Acoustic Formula). This clang 

 coincides exactly with the resonance fundamental tone of the sound-conducting apparatus of the 

 ear itself. 



