NERVOUS SYSTEM. INVERTEBRATA. 61 



D. 63. The isolated nervous system of a Cuttle-fish {Sepia officin- 

 alis) showing the origin and course of the main nerves. 



The innervation area of the cerebral ganglion includes 

 the eyes (through the mediation o the optic ganglia), (he 

 olfactory pit, the otocyst (by nerves that perforate the 

 suboesophageal mass), and, indirectly through the supra- 

 pharyngeal ganglion, the lips. 



The anterior (pedal) region of the suboesophageal mass 

 is composed of a brachial and an infundibular centre. The 

 brachial nerves arise from the anterior margin of the 

 former ; they are 10 in number 8 for the non-retractile 

 arms and 2 for the tentacles. Just before the separation 

 of the 8 arms from their common muscular base, their 

 nerves are united together by a circular commissure, the 

 main part of which enters a small ganglionic enlargement 

 upon each brachial nerve, while a smaller strand leaves the 

 commissure on one side of the ganglion, passes across its 

 inner surface, and joins the commissure again on the other 

 side. In the free part of each arm the nerve is central in 

 position and ganglionic. The nerves for the anterior part 

 of the funnel arise from the ventral surface of the in- 

 fundibular centre their extremities can be seen in the 

 specimen projecting beyond the optic ganglia. 



A pair of large mantle-nerves are given off from the 

 lateral posterior corners of the pleuro-visceral centre. 

 Each of them runs diagonally backwards to the retractor 

 capitis muscle ; at this point it gives off a branch from 

 its inner margin, and then passes through the substance of 

 the muscle to the dorsal wall of the mantle- cavity. Here 

 it divides into two branches, one of which shortly enters a 

 large round ganglion (g. stellatum), from which nerves 

 radiate to all parts of the mantle ; the other passes along 

 the median surface of the stellate ganglion and is distri- 

 buted to the lateral-fin fold. The posterior infundibular 

 nerves arise slightly in front of the pallial, from the ventral 

 surface of the pleuro-visceral centre. The visceral nerves 

 are given off close side by side from its posterior border. 

 They run backwards to the ventral surface of the gastric 

 gland, perforate the subhepatic cartilage and continue close 

 beneath the skin, one on either side of the cephalic vein to 



