HELIX — NERVOUS SYSTEM. 
149 
more completely so in adults ; the anterior pair, known as the pleural 
ganglia, are joined by connectives with the cerebral ganglia, but are 
in actual contact with the pedal centres and with each other ; the 
pallial, known also as the visceral or intestinal ganglia, are placed 
more posteriorly and intimately fused with each other and to the 
more anterior pleural ganglia of their respective sides ; the termina- 
tion of the visceral loop is formed by an abdominal ganglion, which 
is closely adherent to and between 
the right and left pallial ganglia. This 
gTOup of ganglia innervates the body 
wall, three sets of nerves being given off 
fi-om the right and two from the left side 
for this puiiiose, which enter the tissues 
at the base of the visceral sac ; the re- 
productive glands are innervated by a 
strong nerve from the abdominal ganglion 
which accompanies the posterior aorta 
and sends a branch to the heart; many 
fibres also enter and anastomose within 
the glandular mantle margin and in- 
nervate the mantle and its organs, and 
the viscera generally receive their nerve 
supply troni this centre, which fulbls the 
role of a sympathetic system, regulating 
the involuntary motions of the alimentaiy 
and other organs. 
The buccal or stomato-gastric ganglia 
are small but distinct reniform nervous 
masses which do not fuse together as do 
the various other ganglia ; they are placed 
at the sides of the buccal cavity, near 
the outlets of the salivaiy ducts ; con- 
nected by a delicate commissure passing beneath the oesophagus and 
joined by pigmented connectives to the under surface of the cerebral 
ganglia, they give off nerves to the mouth, the oesophagus and stomach. 
The buccal mass has play backwards and forwards through the 
cerebro-visceral nerve-ring, involving the buccal ganglia in its move- 
ments, so that they may be in front or behind the cerebral ganglia, 
according to the state of retraction or jirotrusion of the buccal bulb. 
F'ig. 309. — Nerve centres from a 
half-grown Helix asj>€rsa, to illus- 
trate the relative positions of the 
various ganglia and the origin and 
distribution of the chief nerves, 
highly magnified. 
a. abdominal ganglion ; y.b. and 
Lb. right and left buccal ganglia ; 
r.c. and l.c. right and left cerebral 
ganglia ; r,p. and l.p. right and left 
pedal ganglia ; 7\pl. and LpL right and 
left pleural ganglia ; r.v. and l.v. right 
and left visceral or pallial ganglia; 
c-b.c. cerebro • buccal connective; 
c-p.c. cerebro - pedal connective ; 
c-pl. c. cerebro-pleural connective ; 
c.c. cerebral commissure ; a.p. an- 
terior pedal nerve ; g. nerve to 
ovotestis, with h. branch to heart ; 
/. nerves to lips ; m. to anterior and 
jn to posterior portion of mantle ; 
o. to ommatophore ; cc. to cesophagus 
and stomach ; /. to penis or male 
organ ; ph. to pharynx ; p.p. to 
posterior part of foot ; s.d. to salivary 
ducts ; t. to lower tentacle and Ups. 
