CRANIAL NERVES. 



835 



passes between the malleus and incus, giving a branch to the lat- 

 ter, and then enters the zygomatic fossa. The chorda tympani then 

 descends between the two pterygoid muscles to meet the nerve of 

 taste. After communicating, with the latter it accompanies it to the 

 submaxillary gland. There it joins the submaxillary ganglion to 

 terminate in the lingual nerve. 



Physiology. While the trigeminus is responsible for the sen- 

 sibility of the face, the facial presides over the contraction of the 

 facial muscles of expression. 



The facial nerve is purely motor, and so has nothing to do with 

 tne transmission of sensory impressions developed upon the face. 

 After its section the skin still preserves all of its sensibility. On 

 the other hand, after section of the trifacial it completely disap- 

 pears. Though the facial does not transmit sensory impressions, yet 

 in itself it is sensitive because of the branches which it receives from 

 the trigeminus. If the nerve be pinched, the animal shows signs 

 of pain. 



Pathology. -The facial is the motor nerve which suffers most 

 easily from the influence of cold. Facial paralysis, or BelFs palsy, 

 may occur very easily when draughts from a window blow upon the 

 face. 



When the paralysis is unilateral, the face is drawn toward the 

 sound side. The labial commissure on the paralyzed side is lower 

 than that on the other side, thus giving to the mouth an oblique 

 direction. 



BelFs paralysis is usually due to a cold draught of air striking 

 the nerve at its exit from the stylo-mastoid foramen. When the 

 cause is seated in the brain the external rectus is usually affected, 

 because its nerve, is also involved and usually there is paralysis of 

 the opposite half of the body, or crossed paralysis. Here the lesion 

 is in the pons. If the lesion is seated in the petrous portion of the 

 temporal bone, there is not only facial palsy, but also loss of taste 

 from an involvement of the chorda tympani. 



EIGHTH PAIR, OR AUDITORY NERVE. 



The anatomy and function of this nerve have been discussed in 

 Chapter XVIII. 



NINTH PAIR, OR GLOSSO-PHARYNGEAL NERVE. 



The glosso-pharyngeal nerve is a nerve of both motion and sen- 

 sation, 



