THE RABBIT. 105 



C. Mixed nerves, ganglionated at the root. 



v. Trigeminal. 

 vn. Facial, 

 ix. Glossopharyngeal. 

 x. Vagus or pneumogastric. 



D. Purely motor nerves (to muscles of neck and tongue). 



xi. Spinal Accessory. 

 xn. Hypoglossal. 



In describing each of these cranial nerves there are 

 three points to be noted origin, course, and distribution. 



By origin is meant the part of the brain with which the 

 nerve is visibly connected (sensory as well as motor nerves 

 being spoken of as running from the brain outwards). 

 More strictly this is its superficial origin, for the individual 

 nerve-fibres may run some way through the brain itself 

 before they terminate in nerve-cells or in ramifications 

 around nerve-cells. But this deep or internal origin is only 

 determined by great refinements of investigation, and for 

 our purpose the superficial origin will in most cases suffice. 



The course of a cranial nerve is not always straight to its 

 destination, as might be expected. The peculiarities in the 

 course of nerves are often quite incomprehensible from the 

 point of view of the particular type studied, but may be 

 explained by a comparison with other types, as we shall see 

 in several cases. 



The distribution of a nerve means the distribution of the 

 ends of its fibres remote from the brain, whether in nerve- 

 cells or in ramifications. 



9. Olfactory and Optic Nerves. These nerves differ 

 from all other cranial and spinal nerves in that they consist 

 of fibres whose nerve- cells, instead of being situated either 

 in the central nervous system or in ganglia at the sides of 

 it, are situated in the sense-organ viz. in the olfactory 

 membrane of the nasal passages, and in the retina of the 

 eye, respectively. On strict morphological grounds we 

 ought not to count these as nerves at all, but rather as 

 tracts of white matter constituting outlying parts of the 



