524 MANUAL OF PHYSIOLOGY. 



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 internal 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 toward the hiatus, and 

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

 ulate ganglion), and then runs backward along the top of the 

 inner wall of the drum, and passing downward 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 connections 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 

 circuitous 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 

 superficial petrosal nerve, which sends a branch to the otic gan- 

 glion, whence the fibres pass to the auriculo temporal nerve, and 

 then on to the gland. (2) To the submaxillary gland by the 

 chorda tympani, which after traversing the tympanum leaves 

 the ear by a fissure at its anterior extremity, then joins the 

 lingual branch of the fifth to separate from it and pass into the 

 submaxillary ganglion which lies in close relation to the gland 

 (compare Figs. 64 and 65). 



