326 



INNEKVATION. 



[CHAP. xi. 



Fig. 73. 



excito-motory. The former author describes the nerves of articulata 

 as consisting of fibres derived from two sources namely, the ante- 

 rior or cerebral ganglion, and the ganglion of that segment of the 

 body to which they belong. Those fibres which are connected with 

 the brain, he states, pass down along the dorsal surface of the gan- 

 glionic chain, and are fibres of sensation and voluntary motion ; 

 those which are immediately implanted in the ganglia are excito- 

 motory. Mr. Newport, in his recent able and elaborate description 

 of the nervous system of Myriapoda, thinks that he shews a some- 

 what similar arrangement in those animals. The ganglionic chain 

 has on its dorsal surface a pair of columns, superior longitudinal 

 fibres, which pass over the ganglia, sending a few fibres to mingle 



with them, or with an inferior 

 pair of longitudinal columns. 

 These latter, the inferior longi- 

 tudinal fibres, are placed along 

 the abdominal surface of the 

 ganglionic chain, and are inti- 

 mately connected with the gan- 

 glia. In the intervals between 

 the ganglia these two columns 

 lie in close juxtaposition, sepa- 

 rated only by some transverse 

 fibres. The inferior columns 

 appear, as Mr. Newport states, 

 to receive fibres from the supe- 

 rior columns, and probably to 

 send some to them, " thus de- 

 cussating each other in the 

 middle substance of the cord, 

 where these two longitudinal 

 series are in close apposition ; 

 since it is almost impossible, 



Upper and under surfaces of a portion of the cord in 6V6n in the large nervOUS COrd 



Spirostreptus. After Newport. /? ct i i 



A. Under surface. B. Upper surface. Ol bCOlOpendra, to Separate 



a. Inferior longitudinal fibres, e. Superior longitu- , -_ ~ 



dinal fibres. /. Fibres of reinforcement, also seen at tlieSC TWO tracts ITOm CaCll 



ftandc. g. Commissural fibres, also seen at d, A. ,-, -i.-i T ,-, ->- ,- 



other, although their distinct- 

 ness is evinced in their relative size and longitudinal line of separa- 

 tion."* The ganglia, then, are placed between these two columns 

 the inferior pair being intimately connected with them. Almost the 



Phil. Trans. 1844. 



