NERVES OF THE ENCEPHALON. 381 



The Pneumogastric Nerve (Nervus Pneumogastricus or Vagus, 

 of Eighth Pair,) arises from the corpus restiforme of the medulla 

 oblongata, just behind, or on the borders of the fissure separating 

 it from the corpus olivare, somewhat above, and posterior to>Jjbe 

 highest root of the accessory nerve. It commences by a num- 

 ber of parallel filaments, varying in number from ten to fifteen, 

 which are placed very near each other, so as to form two or 

 three flattened fasciculi of half an inch or more in length. The 

 fasciculi below adhere to the spinal accessory, and those above 

 to the glosso-pharyngeal nerve. The fasciculi, finally, collect 

 into a single flattened cord of one and a half lines in breadth. 



This cord goes outwards and backwards to the foramen lace- 

 rum posterius, and gets through it in front of the internal jugular 

 vein, being separated from the latter by the small spine which 

 arises, from the pars petrosa of the temporal bone. It passes 

 through its own canal in the dura mater, being thus kept distinct 

 from the glosso-pharyngeal, and from the accessory nerve, and 

 in this canal the fasciculi which form it are collected into a single 

 cylindrical trunk. After getting through the canal it then ad- 

 heres, by a close, strong, cellular substance, to the glosso-pharyn- 

 geal and to the accessory. 



The general plan of distribution of the pneumogastric nerve 

 is, as its name implies, to the organs of respiration, and to the 

 stomach. 



The Accessory Nerve (Nervus Accessorius, of Eighth Pair,) 

 arises from the posterior fasciculus of the medulla oblongata, just 

 behind the nervus hypoglossus, and also from the posterior fasci- 

 culus of the medulla spinalis, sometimes as low down as the 

 seventh cervical nerve. There are six or seven roots from the 

 medulla spinalis, and about three or four from the medulla ob- 

 longata: the former are single, and run, successively, into the 

 same trunk; but the latter are each composed of two branches, 

 consisting respectively of two or more filaments. These roots 

 are, successively, larger and longer, as they ascend to join the 

 common trunk. The latter goes up between the posterior fasci- 

 culi of spinal nerves and the ligamentum denticulatum, and gets 

 into the cavity of the cranium, behind the vertebral artery, 

 through the foramen magnum occipitis. It is joined sometimes 



