286 THE NERVOUS SYSTEM 



less it be an explanation to say that the inflammation is set 

 up by the impairment of nutrition in these structures the 

 impairment resulting in part from the impoverished condi- 

 tion of the blood as a consequence of the inability of the 

 animal to chew. 



Sixth Nerve (Abducens). 



Origin. This is a motor nerve entirely. Its apparent 

 origin is from the lower border of the pons in the groove 

 separating it from the anterior pyramid of the medulla. Its 

 deep origin is close to the median line beneath the floor of 

 the fourth ventricle a little below the motor root of the fifth. 



Course and Distribution. The nerve enters the cavern- 

 ous sinus, runs forward to enter the orbit by the sphenoidal 

 fissure, passes between the two heads of the external rectus, 

 and is distributed to the ocular surface of that muscle. In 

 the cavernous sinus it receives fibers from the first division 

 of the fifth and from the sympathetic. 



Function. The function is indicated in its distribution. 

 It is insensible at its origin. Stimulation produces contrac- 

 tion of the external rectus ; section causes paralysis of that 

 muscle and consequent internal strabismus and diplopia. 



Seventh Nerve (Facial). 



Origin. The apparent origin of the seventh is from the 

 upper end of the medulla in the groove between the olivary 

 and restiform bodies. Its deep origin is in the pons beneath 

 the floor of the fourth ventricle a little external to the nu- 

 cleus of the sixth. 



Course and Distribution. The seventh nerve passes out- 

 ward and forward with the auditory nerve (on its inner 

 side) to enter the internal auditory meatus. From their 

 relative firmness and texture and their close relation here, 

 the seventh and eighth nerves have been called respectively 



