628 TEXT-BOOK OF PHYSIOLOGY. 



face corresponding to the lesion; separation of the eyelids from paralysis of 

 the orbicularis palpebrarum and the unopposed contraction of the levator 

 palpebrse muscle; abolition of the ability to wink; drooping of the angle of 

 the mouth; an escape of saliva from the mouth; contraction of the muscles 

 and distortion of the opposite side of the face; on attempting to laugh 

 or talk the distortion of the face is increased; during mastication the food 

 accumulates between the teeth and cheek, from paralysis of the buccinator; 

 articulation is impaired from paralysis of the orbicularis oris muscle, the 

 labial sounds especially being imperfectly produced. 



Functions. The function of the facial nerve is the transmission of 

 nerve impulses from the nerve-cells in which it arises to the superficial 

 muscles of the face, those more especially concerned in the expression of the 

 feelings. By reason of the association of the cortical facial area and the 

 nucleus of origin of the facial nerve the latter becomes the medium of 

 communication between the cortical area <md the facial muscles and serves 

 for the transmission to the muscles of those nerve impulses developed by 

 and associated with psychic states. The muscles thus excited to action 

 individually and collectively express in a general way the character of 

 the psychic state. For this reason the facial nerve is termed the nerve of 

 expression. 



Branches of the Facial Nerve ; Their Origin, Properties and Func- 

 tions. The branches usually described in works on anatomy as coming 

 from the facial nerve are as a matter of fact, not branches of the facial nerve 

 proper (with one exception, viz. : the tympanic) but are branches of autonomic 

 nerves (vaso-motor and secretor) which after leaving the central nerve sys- 

 tem enter the sheath of the facial. After a short distance, however, they 

 leave it to be distributed around sympathetic ganglia. In one of these 

 branches (the chorda tympani) afferent nerve-fibers are present which minis- 

 ter to the sense of taste. These fibers very naturally cannot be regarded as 

 integral parts of the facial proper. 



Between the facial and the acoustic nerve there is a small nerve known 

 as the pars intermedia, the nervus iritermedius or the nerve of Wrisberg. The 

 true nature of this nerve has long been a subject of investigation. The 

 results of histologic investigation and physiologic experimentation would 

 indicate that it is composed of both efferent and afferent fibers. The efferent 

 fibers which constitute in part the nerve of Wrisberg have their origin in a 

 group of cells situated beneath the floor of the fourth ventricle near the 

 median line between the nucleus of the facial and the nucleus of the motor 

 root of the trigeminal nerve and known as the nucleus salivatorius. The 

 afferent fibers arise from nerve-cells composing in large part the ganglionic 

 enlargement found on the genu of the facial nerve at the point where it turns 

 backward to enter the aqueduct of Fallopius. The cells of this geniculate 

 ganglion, originally bipolar present single axons which soon divide into 

 centrally and peripherally coursing branches. The centrally coursing 

 branches constitute in part the nerve of Wrisberg, which entering and pass- 

 ing through the pons terminates directly or indirectly around the sensor 

 end-nucleus of the glosso-pharyngeal nerve. The peripherally coursing 

 branches enter the sheath of the facial nerve and accompany it as far 

 as a point about 5 millimeters above the stylo-mastoid foramen. 



From its mode of origin, the nerve of Wrisberg cannot be regarded as 



