NERVOUS SYSTEM. 



219 



brain, a second nervous ring is formed around the oesopha- 

 gus in the cephalopods, as in most of the gasteropods and 

 pteropods. On opening the skull of the argonauta from be- 

 hind, as in the annexed figure (Fig. 94,) by Chiaje, the brain 

 (fl,) of a round form above, separated from the inner parietes 



FIG. 



r" 



of the skull by the gelatinous arachnoid, and extending 

 downwards to encompass the oesophagus (i,) is observed to 

 give off laterally the large optic nerves (^,) which perforate 

 the cranium to reach the pedunculated eyes, and from its 

 more anterior portion the separate great symmetrical columns 

 (94. b, b,) which extend backwards to the palleal ganglia (94. 



