ORIGIN OF THE ENCEPHALIC NERVES. 591 



The nerve ascends on the side of the medulla, between the 

 ligament and the posterior roots of the nerves, and continues 

 to receive filaments of origin from the medulla as high up as 

 the roots of the pneumogastric with which the radical filaments 

 of this nerve seem continuous. It receives filaments as it 

 passes by, from the posterior root of the sub-occipital, and is 

 sometimes connected with the posterior root of the first proper 

 cervical. It passes up through the occipital foramen, and goes 

 out from the cavity of the cranium in conjunction with the par 

 vagum, with which it has been considered associated as a 

 motor nerve for the external respiratory muscles. It is a round 

 nerve like the third or the sixth. 



The pneumogastric or par vagum, is a mixed nerve in its 

 distribution, in consequence of its receiving motor filaments 

 from the spinal accessory and other nerves, which are wrapped 

 up in its general sheath. It is believed, however, to be a sen- 

 sory nerve, entirely, at its origin from the lateral tract of the 

 medulla oblongata, immediately behind the corpus olivare, where 

 it consists of from seven to fourteen flattened fasciculi. 



The glosso-pharyngeal, is believed to be a compound nerve, 

 giving nerves of sensation to the mucous membrane of the back 

 part of the tongue and to the fauces, and nerves of motion to 

 some of the muscles of the pharynx. It originates by two roots, 

 which seem to come partly from the lateral tract, and partly from 

 the corpus olivare, immediately above the pneumogastric. It 

 has been considered the special nerve of taste ; but the nerve 

 of taste appears not to be a distinct trunk. The fibres endowed 

 with this function, are probably included in the branches of the 

 glosso-pharyngeal and the fifth. The three latter nerves, spinal 

 accessory, pneumogastric and glosso-pharyngeal make the eighth 

 pair of the old anatomists. 



The auditory nerve, (portio mollis of the seventh pair,) is ex- 

 clusively one of sensation ; it originates by two roots, one of 

 which passes through the substance of the medulla oblongata, 

 and takes its origin from the corpus restiforme. The other winds 

 round the restiform body, and arises from the medullary striae in 

 the cineritious substance of the fourth ventricle. 



