THE CRANIAL NERVES. 



519 



Section V.— NEUROLOGY. 



The nervous system consists of central and peripheral parts. To 

 the first belong those large masses of nervous substance forming the 

 brain and spinal cord, or great cerebro-spinal centre ; and to the second 

 belong the various nervous cords, cerebro-spinal and sympathetic, which 

 are distributed in diflFerent parts of the body. Along with these the 

 nervous system also includes the organs of the external senses and the 

 ganglia. 



The description of the cerebro-spinal centre and of the organs of the 

 senses will be given in the Second Volume. The present section in- 

 cludes the descriptive anatomy of the cerebro-spinal and sympathetic 

 nerves, and of the ganglia connected with them. 



THE CEREBRO-SPINAL NERVES. 



The nerves directly connected with the great cerebro-spinal centre 

 constitute a series of symmetrical pairs, of which a certain number 

 issue from the cranium through diflerent foramina or apertures in its 

 base, and are thence strictly named cranial. The next following nerve 

 passes out between tiie occipital bone and the first vertebra, and the 

 remaining thirty nerves all issue below the corresponding vertebral 

 pieces of the spine. The first is sometimes distinguished by the name 

 of suboccipital, but to the whole series of thirty-one nerves the name 

 of spinal is usually given. 



CRAinAL NERVES. 



The cranial nerves, besides being distinguished by numbers in the 

 order of their passage through the dura mater lining the cranium, have 

 likewise received other names, according to the place or mode of their 

 distribution, or their functions. 



The number of the cranial nerves has been variously stated as nine 

 or as twelve by "Willis and Soemmerring respectively. Of the nine pairs 

 of cranial nerves distinguished by Willis, or twelve as enumerated by 

 Soemmerring, the first six and the last correspond, but the seventh of 

 "Willis is divided into two by Soemmemng, viz., the seventh and the 

 eighth pairs, or the facial and the auditory nerves, while the eighth of 

 AVillis falls, in the more modern arrangement, into three distinct nerves, 

 the ninth, tenth, and eleventh, or the glosso-pharyngeal, pneumogastric 

 and spinal accessory nerves, as in the following table : — 



■\VlLLIS. 



First pair of nerves 

 Second „ 

 Third „ 



Fourth „ 

 Fifth 

 Sixth 



Seventh 



Eighth 

 Ninth 



( portio dura . 

 \ portio mollis 



^ n. vagus 



' n.accessorius 



