834 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



nucleus of the facial nerve, its nucleus being connected with the nucleus 

 of the third nerve on the opposite side. It is the motor nerve of the 

 external rectus muscle of the eye. In co-ordinate movements of the eyes 

 its action is involuntary. It receives fibres from the sympathetic nerve 

 in the neck. 



7. THE FACIAL NERVE. The facial nerve consists solely of efferent 

 fibres, and arises by two roots from the floor of the fourth ventricle, of 

 which the smaller, through the nerve of Wrisberg, forms a connection 

 with the auditory nerve. The origin of the facial, the facial nucleus, lies 

 behind the origin of the sixth nerve and is connected with the cerebrum 

 of the opposite side. The facial nerve is the motor nerve of the muscles 

 of the face, and hence is called the nerve of expression. It also supplies 

 motor branches to the stylo-hyoid, posterior belly of the digastric, 

 buccinator, stapedius, muscles of the external ear, platysma, and levator 

 palati. It is the secretory nerve of the parotid, and through the 

 chorda tympani of the submaxillary gland. It also contains vaso- 

 motor fibres for the tongue and side of the face and vaso-dilator fibres for 

 the submaxillary gland. Through its anastomoses with the trigeminu^ 

 and vagus it perhaps contains afferent fibres. 



8. THE AUDITORY NERVE. (See Sense of Hearing.) 



9. THE GLOSSO-PHARYNGEAL NERVE. This nerve arises from the 

 glosso-pharyngeal nucleus deep in the medulla oblongata near the olivary 

 body, and is connected with the nucleus of the vagus. An ascending 

 root from the spinal cord unites with it and serves for the production of 

 spinal reflexes. It is supplied to the palatine and pharyngeal muscles, 

 but its motor function to these muscles is not absolutely established ; 

 possibly its motor fibres are derived from the facial. It is the nerve of 

 taste for the back of the tongue and pharynx, as well as being the nerve 

 of general sensation for these parts, the Eustachian tube and tympanum. 



10. THE PNEUMOGASTRIC NERVE. The vagus nerve has a common 

 nucleus with the ninth and eleventh nerves in the ala cinerea in the 

 lower half of the calamus scriptorius. It contains both afferent and 

 efferent fibres, the latter, probably, being derived from the spinal-acces- 

 sory. The efferent fibres are distributed to the muscles of the pharynx, 

 larynx, trachea, bronchi, oesophagus, stomach, and intestines. It is also 

 the inhibitory nerve of the heart, and contains vaso-motor fibres for the 

 lungs and trophic fibres for the lungs and heart. It is the sensory nerve 

 for the external ear, pharynx, oesophagus, stomach, and respiratory 

 passages. It contains afferent fibres, which may augment or inhibit 

 (laryngeal nerve) the respiratory centre, augment the cardio-inhibitory 

 centre, inhibit the medullary vaso-motor centre (depressor nerve) ; 

 through it afferent impressions may pass which produce the salivary or 

 inhibit the pancreatic secretions. 



