242 MARTIN F. WOODWARD. 



view (fig. 21) shows a nerve arising just between the fourth 

 and fifth lip-nerves ; this nerve, the buccal nerve (6. n.), 

 curves sharply up over the muscular odontophore, giving off 

 branches on its course. After ascending for some distance 

 it bends sharply back and becomes greatly enlarged, and 

 may now be spoken of as the buccal ganglion (figs. 8 and 29, 

 h. g.). This ganglion is a curiously elongate structure, and 

 gives off branches anteriorly and ventrally ; while the main 

 mass is continued back under the radular sac, where it unites 

 with its fellow fi'om the opposite side (fig. 27). A very con- 

 spicuous branch arises from the middle of the dorsal border of 

 the ganglion, which curving upwards and backwards runs along 

 the salivary duct and supplies the salivary gland (figs. 8 and 29). 



From the posterior border of the cerebral ganglia two very 

 large cords arise, these represent the cerebro-pleural and 

 cerebro-pedal connectives ; of these the former and more 

 posterior cord is as usual much the larger. As with the 

 other parts of the nervous system, ganglionic cells are 

 scattered along the length of these cords, more especially at 

 the periphery, and more abundantly in the cerebro-pleural 

 than in the cerebro-pedal connective (fig. 22). 



The cerebro-pedal connective passes back, taking at first a 

 somewhat horizontal position, but eventually curving down- 

 ward to join the great scalariform pleuro-pedal cords. It is 

 closely followed by the cerebro-pleural connective, and the 

 two become reunited near the posterior border of the great 

 odontophoral muscular mass. The combined pleuro-pedal 

 mass then enters the foot, where it becomes connected by 

 a transverse commissure with the coi*responding structure 

 from the opposite side (figs. 21 and 27). This transverse 

 commissure contains elements derived from both the pleural 

 and pedal systems (fig. 21). 



The Pleuro-pedal Cords. — Although the pleural and 

 pedal cords are now closely connected, they can still be dis- 

 tinguished from one another by the presence of a groove 

 which runs along the whole length of the combined pleuro- 

 pedal cord (figs. 28 and 29) . 



