THE CEPHALOPODA 
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all Cephalopods. In Nautilus the stomato-gastric commissure passes 
under the pharynx immediately behind the radula and bears a 
buccal ganglion (Fig. 279, VII) on either side. 
In the Dibranchia the nerve-centres are much more completely 
enclosed in the cartilaginous cephalic capsule than in Nautilus, and 
consequently many nerves—notably the pallial nerve—traverse the 
cephalic cartilage at their origin. The cerebral centres themselves 
appear externally to be unpaired, and in the Decapoda they are 
divided transversely into a small anterior (Fig. 282, III) and a 
large posterior lobe, the latter being separated by some considerable 
distance from the former in various Oigopsida, such as Ommato- 
strephes (Fig. 282, IV), Spirula, ete., but the distance is less in Sepiola 
Fic. 279. 
Nautilus, central nervous system, left-side view. I, radula ; II, stomato-gastric commissure ; 
III, cerebral ganglion, with the optic nerve in section; IV, visceral ganglion ; V, oesophagus ; 
VI, pedal ganglion; VII, stomato-gastric ganglion; VIII, root of the labial commissure ; IX, 
labial commissure ; X, ‘‘ tongue”; 0, otocyst. 
and Loligo, and is very small in Sepia. These two lobes are united 
by a pair of slender connectives, which are sometimes fused together 
for a certain distance. In the Octopoda, on the other hand, the 
cerebral mass is apparently single, the two lobes above mentioned 
being intimately fused together, and their limits are barely indicated 
by a transverse furrow, behind which is the posterior lobe with six 
longitudinal furrows on its surface. The cerebral centres of all the 
Dibranchia give off a large optic nerve on either side, each nerve 
expanding to form a very large ganglion, whose size is greater than 
that of the whole mass of the cerebral centres. As in Nautilus, a 
labial commissure is given off from the anterior part of the cerebral 
centres (Fig. 279, IX), and the stomato-gastric commissure originates 
from the labial commissure. Finally, the cerebro-pedal pair of 
connectives issues from the anterior part of the cerebral mass ; 
these connectives are simple in the Octopoda (Fig. 281), but in the 
