428 



MOLLUSCA. 



the buccal mass. This stomatogastric system (Fig. 343) consists of 

 the two above-mentioned nerves (c.c) on each side, which pass forward 

 from the cerebral ganglion to end in the two pharyngeal ganglia 

 (ph. g). These are connected by a long anterior commissure (ant. 



com} which passes ventral 

 to the mouth, and by a 

 shorter posterior commis- 

 sure, the buccal commis- 

 sure (buc. phar. com. and 

 b. com.) which is also 

 ventral to the oesophagus, 

 and contains in its course 

 two buccal ganglia (buc.g.). 

 The ganglia and commis- 

 sures of the stomatogastric 

 system supply the buccal 

 mass. In the female there 

 is an accessory ganglion 

 supplying the inner ven- 

 tral cephalic lobe, and 

 connected with what has 

 been called above the 

 pedal ganglion (Fig. 

 342, /). 



bvc.phw con 



FIG. 343. Buccal nervous system of Nautilus pompilius 

 (after Graham Kerr). ph.g pharyngeal ganglion ; 

 Zmc.gr buccal ganglion (buc.g ought to point to the 

 swelling from which the nerves ph. n come off) ; 

 c.c cerebro - pharyngeal connective; buc.phar.con 

 bucco - pharyngeal connective ; ph.n pharyngeal 

 nerves ; b.com buccal commissure (stomatogastric) ; 

 ant.com anterior pharyngeal commissure. 



It should be noted that the nerves to the cephalic arms come off rather high 

 up on the anterior ring, and that the nerve to the funnel arises quite ventrally. 



In the Dibranchs 

 the great nerve 

 centres are com- 

 pletely enclosed in 

 the skull. As in 

 Nautilus it is difficult 

 to speak of special 

 ganglia, for the whole 

 mass is ganglionic. 

 The part dorsal to 

 the oesophagus we 

 may call the cerebral 

 ganglion (Fig. 344, 1); 

 this gives off later- 



FIG. 344. Central nervous system of Ommatostrephes from 

 the left side, magnified (after Pelseneer). a buccal mass ; 

 6 brachial ganglion ; c oesophagus ; d pedal ganglion ; e 

 nerve of the funnel ; / position of the otocyst ; g pleuro- 

 visceral ganglion ; h visceral nerve ; i posterior salivary 

 gland ; j pallial nerve ; k optic nerve, cut ; I cerebral gan- 

 glion ; m stomatogastric (buccaJ) ganglion ; n anterior part 

 of the cerebral ganglion (suprabuccal) ; o anterior salivary 

 Bland. 



