522 MANUAL OF PHYSIOLOGY. 



paralysis of this nerve a double image is seen only when looking 

 downwards, and the image on the affected side is oblique and 

 below that seen by the sound eye. 



VI. THE ABDUCTOR NERVE OF THE EYE. 



This arises in the floor of the fourth ventricle, and appears just 

 below the pons Varolii. It is the motor nerve of the external 

 rectus muscle of the eye. Paralysis or section of it causes inter- 

 nal squint. 



VII. (PoRTio DURA) MOTOR NERVE OF THE FACE. 



This nerve arises from a gray nucleus in the floor of the fourth 

 ventricle. It passes with the other part of the seventh (portio 

 mollis) or auditory nerve into the internal auditory meatus of the 

 temporal bone. It first passes out towards the hiatus, and then 

 turns at a right angle to form a knee-like swelling (geniculate 

 ganglion), and then runs backwards along the top of the inner 

 wall of the drum, and passing downwards through a special canal 

 in the bone, comes out at the stylo-mastoid foramen, and finally 

 spreads out on the side of the face. It is essentially an efferent 

 nerve, being partly motor and partly secretory, though its con- 

 nections have caused afferent functions to be ascribed to it. Its 

 distribution may be thus briefly summarized : 



i. Motor fibres. (1.) To the muscles of the forehead, eyelids, 

 nose, cheek, mouth, chin, outer ear, and the platysma, which may 

 be grouped together as the muscles of expression. (2.) To some 

 muscles of mastication, viz., buccinator, posterior belly of digastric, 

 and the stylo-hyoid all the foregoing being supplied by external 

 branches while in the temporal bone it gives a branch to (3) 

 the stapedius muscle, and also a branch from the geniculate gan- 

 glion named the great superficial petrosal nerve, which after a cir- 

 cuitous course is supplied to the elevator and azygos muscles of 

 the palate and uvula. 



ii. Secretory fibres. (1.) To the parotid gland by the small su- 

 perficial petrosal nerve, which sends a branch to the otic ganglion, 

 whence the fibres pass to the auriculo-temporal nerve, and then 



