76 ZOOTOMY. 



division : the latter (F b , F/7, VIIT) contains the remainder 

 of the fifth, the seventh, and the eighth nerves. 



The fifth, seventh, and eighth nerves arise altogether by seven roots. 

 Two of these, a smaller dorsal (Fig. 26, F a/ ) and a larger ventral (F a ) 

 go to form the anterior fasciculus already mentioned, both arising ventro- 

 laterally from the medulla. The five roots forming the posterior fasci- 

 culus divide naturally into an anterior and a posterior set. The anterior 

 set consists of two roots, a dorsal ( VII] and a ventral ( VII 1 }, together 

 forming the seventh nerve : the posterior set consists of three roots, a 

 dorsal (V b ), arising along with the dorsal root of the seventh, and two 

 ventral, arising close together : the uppermost ventral root unites 

 immediately with the dorsal root to form the remainder of the fifth 

 nerve (F b ) : the lowermost ventral root (VIII} constitutes the eighth 



187. The sixth pair (abducentes, Figs. 22 and 23, VI) 

 arise from the under surface of the medulla oblongata, 

 internal to the eighth. They are very fine nerves, and are 

 easily detached with the pia mater. 



188. The ninth pair (glossopharyngei, Figs. 22, 23, 

 25, IX), a small pair arising from the sides of the medulla 

 oblongata, and passing outwards and forwards to enter the au- 

 ditory capsule at about the centre of its inner surface ( 33). 



189. The tenth pair (vagi or pneumogastrici, Figs. 22, 

 23, 25, X), arise by several roots from the lateral regions 

 of the hinder part of the medulla oblongata, and pass out- 

 wards and backwards to leave the cranial cavity by a foramen 

 in the posterior part of the inner surface of the auditory 

 capsule (33). 



XLI. Remove the skin from the dorsal surface of the 

 head, on both sides of the cranial cavity, and by 

 carefully dissecting away the connective tissue 

 from the eye and surrounding parts, make out 



190. The dorsal ramus of the orbito-nasal nerve (first 

 division of the fifth, Figs. 22 and 27, F' a ) lying close 



