450 THE ANATOMY OF IXVERTEBRATED ANIMALS. 



The nervous system in the Cephalopoda^ as in other Mol- 

 lusca^ consists of cerebral, pedal, and parieto-splanchnic gan- 

 glia, aggregated around the gullet, and connected by com- 

 missural cords. In addition to these, buccal, visceral, bran- 

 chial, and pallial ganglia may be developed on the nerves 

 which supply the buccal mass, the alimentary canal, heart, 

 branchia, and mantle. 



In the Dibranchiata (Fig. 128), the three principal pairs 

 of ganglia are usually large, and so closely aggregated to- 

 gether that the commissures are not readily distinguishable. 

 The optic nerves are very large ; one or two nerves are given 

 oflF to the superior or anterior buccal ganglia, which have co- 

 alesced into one mass, and are united by commissures, which 

 encircle the oesophagus, with the coalesced inferior or pos- 

 terior buccal ganglia. The pedal ganglia lie on the pos- 

 terior side of the gullet, and supply the large nerves to the 

 arms, and those to the funnel, while the auditory nerves are 

 immediately connected with them. Each parieto-splanchnic 

 ganglion gives off a nerve which runs along the shell-muscles 

 to the anterior wall of the mantle, and there enters a large 

 ganglion, the ganglion stellatiim. A large median branch, or 

 branches, from the parieto-splanchnic ganglia, accompanies 

 the vena cava, and is distributed to the branchiae and sexual 

 organs. The inferior buccal ganglion sends a recurrent nerve 

 along the oesophagus, which ends in a ganglion on the stom- 

 ach.^ 



The nervous svstem of JS^aidilus differs in some important 

 particulars from "that of the Dihranchiata. The cerebral 

 ganglia are represented by a thick transverse cord, which lies 

 in front of the oesophagus, and from the outer angles of which 

 the optic and olfactory nerves are given off, while nerves to 

 the buccal mass proceed from its anterior edge. The pedal 

 ganglia lie close to the cerebral ganglia, and are united by a 

 slender commissure, which passes behind the gullet. They 

 supply all the brachial processes and the funnel with nerves, 

 and the short auditory nerves are connected with them. The 

 parieto-splanchnic ganglia are, like the cerebral ganglia, elon- 

 gated, and together constitute a thick cord, which, united at 

 each end with the cerebral ganglia, forms a hoop round the gul- 

 let, distinct from the pedal nerve-arch, and separated from it 

 by a process of the cartilaginous skeleton. The largest nerves 



» See Hancock, " Anatomy of the Nervous Svstem of Ommastreplies.^^ 

 (" Ann. Nat. Histoiy," 1852.) 



