314 THE CEPHALOPODA 
Decapoda there are two on each side, namely, the cerebro-pedal and 
the cerebro-brachial. The ventral or sub-oesophageal nervous mass 
is formed by the visceral and pedal centres: these are fairly closely 
united together (as they are, for instance, in Helix), and are only 
separated in the middle line to admit of the passage of.an aortic 
vessel which runs dorsad of the visceral and ventrad of the pedal 
centres ; a similar arrangement occurs in sundry Gastropods. 
The pedal ganglia are divided transversely into two distinct pairs, 
the anterior or brachial and the posterior or pedal ganglia proper 
n.visc. 
n.sup.br 
X fo 
Fic. 280. 
Diagram of the nervous system of a female Nautilus pompilius, ventral aspect. cer, cerebral 
ganglion ; m, nerves to the mantle; n.inf-br, posterior branchial nerve ; ».olf, olfactory nerve 
terminating under the olfactory papilla; n.suwp.br, anterior branchial nerve; 7.visc, genito- 
branchial nerve, or chief visceral nerve; n.#, nerve accompanying the vena cava, which lies 
between this and the similar nerve of the right side; olf.p.p, the right olfactory papilla; opt, 
optic ganglion ; ov, the oviduct ; ped, pedal ganglion ; pl, pallial part of the visceral ganglionic 
commissure ; «and y, ganglion-like enlargements on pedal nerves to the median lobe of the 
inner circlet of the circumoral tentacular lobes. (After Ray Lankester and Bourne.) 
(Fig. 282, XII, XIV). This division is most marked in the Oigopsida 
(Ommatostrephes, Spirula, Fig. 268, p.g, ete.), but is less marked in 
Sepia. In all the Decapoda the brachial centres are divided anteriorly 
into ten large nerves which pass into the arms, and anastomose with 
one another at their bases. These centres also have connectives 
joining them to the anterior and the posterior cerebral lobes (Fig. 
282). In the Octopoda the brachial and pedal centres are much 
more closely approximated (Fig. 281), and the former naturally give 
off only eight nerves to the eight arms. The brachial nerve-centres 
extend, together with the arms which they innervate, round either 
side of the oesophagus, and in the Octopoda they meet dorsally and 
