CEPHALOPODA. 617 



arise from the posterior and lateral angles of the sub-oesophageal 

 mass, extend outwards and backwards, perforate the shell-muscles, 

 and form the large stellate ganglions (n, w), from which the nerves 

 of the mantle are principally derived. In the Octopoda this may be 

 described as the termination of the nerve-trunk ; but in the Deca- 

 poda, in which lateral fins are superadded to the body, the great 

 nerve previously divides into two branches, of which the outer one 

 expands into the ganglion, whilst the inner branch, having been 

 joined by one of the rays of the ganglion (o, o), pierces the fleshy 

 substance of the mantle, and ends in a diverging series of twigs 

 appropriated to the muscles of the fin. In proportion as the trunk 

 of the Cephalopod is attenuated and elongated, the pallial nerves 

 become more parallel in their course, more dorsal in their position, 

 and more similar to a rudimental spinal chord of which the two la- 

 teral columns have retained their primitive embryonic separation. 

 The ganglions (n, w) are connected by a transverse commissural nerve 

 in Loligo.* 



The two large visceral nerves (p) arise from the interspace of the 

 origin of the pallial pair; after distributing filaments to the muscles of 

 the neck they descend parallel and close to one another behind the 

 vena cava, give off the small filaments which constitute the plexus 

 upon that vein and around the oesophagus, then diverge fi*om each 

 other towards the root of each gill, where they divide into three prin- 

 cipal branches : one of these dilates into an elongated ganglion (y) 

 and penetrates the fleshy stem of the branchia ; the second descends 

 to the generative organs ; the third passes to the middle or systemic 

 heart. The CESophageal plexus unites into a ganglion (r), attached 

 to the parietes of the gizzard in the interspace between the pyloric 

 and cardiac orifices. Some filaments connect the ganglion with the 

 oesophageal nerve sent off from the buccal ganglion («).f 



With respect to the parts of the brain in the Vertebrata, which are 

 represented by the cephalic nervous masses in the Dibranchiate 

 Cephalopods, we may regard the cordiform superior mass (a), which 

 is principally in communication and coexists with the large and 

 complex eyes, as the homologue of the optic lobes ; it cannot be the 

 cerebellum, as Cuvier supposed, for that body never gives origin to 

 any nerve ; the cerebellum is also less constant than the optic lobes 

 of the Vertebrate brain, and is posterior to them in both position and 

 order of development. The smaller super-oesophageal mass, anterior 

 to the optic lobes in the Octopus and some other cephalopods, may 

 represent an olfactory lobe, or the rudiment of a true cerebrum. I 



* XXIV. & CCLXXVIII. p. 9., pL 1. «. t It- P- 10- 



