vii THE MEDULLA OBLONGATA 405 



section of the trigeminal, which certainly sends sensory and 

 tactile fibres to the isthmus of the fauces, the vomiting reflexes 

 persist. 



Another experimental argument favours the idea that the 

 centripetal fibres of the 9th nerve are exclusively for taste. We 

 know how intimate a relation exists between gustatory sensations 

 and reflex salivation, and Ludwig and Eahn, on stimulating the 

 central end of the divided glosso-pharyngeal, obtained a more 

 abundant secretion of saliva than on exciting the lingual. After 

 bilateral section of the trigeminal nerve in the cat there is an 

 abundant secretion of saliva if the animal is given milk made 

 bitter with quinine. This does not occur on the other hand after 

 bilateral section of the glosso-pharyngeal. All these facts seem to 

 us to favour Panizza's theory. 



The motor fibres of the 9th cranial nerve supply the stylo- 

 pharyngeal muscle and the superior constrictor of the pharynx 

 (Volkmann and Klein). These muscles come into action during 

 the deglutition reflexes, which are readily excited by stimulating 

 the base of the tongue towards the isthmus of the fauces. 



The tympanic or Jacobson's branch, which, as we have seen, 

 conducts the taste fibres by an indirect path to the anterior part 

 of the tongue, also contains secretory fibres for the parotid gland 

 (Vol. II. p. 76). 



VI. The 8th nerve has two roots ; one, the medial or anterior, 

 forms the Vestibular nerve, which pierces the bulb on the 

 inner side of the restiform body and ends in the nucleus in the 

 floor of the fourth ventricle ; the other, the lateral or posterior 

 branch, forms the Cochlear nerve, which passes round the resti- 

 form body, where it has a special nucleus (Fig. 213). These are 

 two distinct nerves, arising, like the dorsal roots of the spinal 

 pairs, from peripheral ganglia ; the first from the vestibular 

 ganglion or ganglion of Scarpa; the second from the spiral 

 ganglion of the cochlea. 



According to Horbaczewsky the vestibular and cochlear nerves 

 run separately, from their origin, in the sheep and horse. After 

 section of the vestibular branch in the sheep (Biehl) and in 

 pigeons (Wallenberg) there is ascending degeneration of the 

 medial roots, which extends as far as the corresponding nucleus. 

 After removing the semicircular canals alone in pigeons the same 

 degeneration results ; but after extirpation of the cochlea only the 

 lateral root degenerates as far as its nucleus (Forel, Onufrowicz, 

 Baginski, Deganello). 



The central relations of the vestibular and cochlear nerves are 

 still doubtful; the former is specially connected with the cere- 

 bellum, the latter with the cerebrum. 



We shall discuss the functions of these two nerves, which 

 together make up the 8th cerebral nerve, in detail, in treating of 



