29S ELEMENTARY BIOLOGY. [CIIAP. 



a. The buccal nen'es. That of the right side will 

 alone be seen ; it arises from the supra-oesophageal 

 ganglion, and passes downwards and forwards to- 

 wards the buccal mass. Trace it with care — it 

 passes beneath the dorsal protractor muscle (see 

 Sect. E. I /'), and terminates in a small buccal 

 ganglion, lying just behind the enlarged base of the 

 salivary-duct. 



Just before it reaches the muscle referred to, it 

 usually gives off two or three branches to the 

 antero-lateral wall of the buccal-mass. 



b. The anterior visceral neiTes ; a system of fibres 

 arising from the above ganglion. The following 

 can be seen with ease. 



a. A ventral branch, distributed to the oesophagus. 



/?. A dorsal one, to the salivary gland, the duct 

 of which it accompanies. 



y. An anterior one, to the roof of the buccal- 

 mass. 



3. Remove the whole nervous system, together with the 

 buccal-mass and tentacle-bearing portion of the 

 cephalic integument. Pin down under water with 

 its posterior end uppermost, and dissect ofif as much 

 as possible of the sheath of the nerve-collar. Note, 

 in addition to the nerves already dissected — 



a. The buccal commissure; a delicate tract of nerve- 

 fibres, seen, on raising the cut end of the oeso- 

 phagus, to connect the buccal ganglia of opposite 

 sides. It passes beneath the gullet. 



