NERVOUS SYSTEM 119 



From their under surfaces a pair of buccal nerves 

 run forwards alongside the oesophagus, and end in a 

 pair of small buccal ganglia placed at the outer sides 

 of the salivary ducts close to their openings into the 

 buccal mass. The buccal ganglia are united by a 

 transverse commissure, and from them nerves arise 

 supplying the buccal mass. 



From the posterior and outer border of each 

 supra-oesophageal ganglion two stout connectives 

 pass downwards and slightly backwards to the sub- 

 cesophageal ganglia. Between these two on each 

 side is the slender auditory nerve. 



2. The sub-oesophageal ganglia are a number of closely 



approximated ganglionic masses, the boundaries of 

 which are difficult to determine. The anterior aorta 

 runs through the centre of the mass, marking the 

 division between the antero-inferior portion, or pedal 

 ganglia, and the postero- superior portion, or viscero- 

 pleural ganglia. 



a. The pedal ganglia are a pair of closely apposed 



masses, from which a number of large nerves 

 pass to the foot. 



b. The viscero-pleural ganglia consist of at least two 



pairs of ganglionic masses, closely apposed to each 

 other and to the pedal ganglia. From them large 

 nerves pass outwards to the viscera and to the 

 body-wall. 



3. The structure of the ganglia. 



Remove one of the ganglia ; place it in weak acetic acid for 

 a short time to soften the connective tissue, and then tease it 

 on a slide in glycerine. Cover ; and examine it with low and 

 high powers. 



The nerve-cells are large granular cells with very 

 large and distinctly reticulate nuclei, and with long 

 branching processes by which they are connected with 

 one another and with the nerve-fibres. 



