SEC. 7. THE CRANIAL NERVES. 



Though we have incidentally dwelt on the functions of all these 

 nerves, it may be as well to recapitulate them in a tabular form. 



1. Olfactory. Nerve of smell. 



2. Optic. Nerve of sight. 



3. Oculo-motor. Motor nerve to the levator palpebrse superi- 

 oris and all the muscles of the eye, except the obliquus superior 

 and the rectus externus. Efferent nerve for the contraction of the 

 pupil and for the muscles of accommodation. Hence when the 

 nerve is divided or otherwise paralysed the upper eyelid falls 

 (ptosis) ; the eye, which is turned outwards, is capable of partial 

 movements only, viz. such as can be produced by the rectus 

 externus and obliquus superior ; when the head is moved, the eye 

 moves with it, the inferior oblique not being able to execute the 

 usual compensating movements of the eyeball ; the pupil is 

 dilated, and the eye cannot accommodate for near distances. The 

 root of the nerve shews recurrent sensibility, due to fibres from 

 the fifth, but is otherwise a purely motor nerve. 



4. Trochlear or Pathetic. Motor nerve to the obliquus 

 superior. When the nerve is paralysed, no marked difference is 

 observed in the position of the eye, but the patient sees double 

 when he attempts to look straight forward or towards the paralysed 

 side ; the images however coalesce when he turns his head to the 

 sound side. When the head is moved from side to side the eye 

 moves with it, the usual compensating movement of the eye which 

 accompanies the movements of the head failing in consequence of 

 the superior oblique not acting. It is a purely motor nerve, but 

 receives recurrent fibres from the fifth. 



