HELIX — NERVOUS SYSTEM. 
I ts 
band connecting its coinponcnt parts above tbe a\sop]iagus anteriorly. 
They give nerves to tlie liead and the neiglibonring organs, large nerves 
arising from their perij)hery which proceed to the onnnatophores and 
the lips, the lower tentacles being innervated chiefly by a branch from 
the labial nerve ; the reproductive organs are also innervated by a 
ner\'e emanating frnm the right side. From them also originate the 
three pairs of connectives 
which are the bonds of con- 
nection between the various 
groups of ganglia and form 
the three more or less closely 
approximate nerve collars 
surrounding the msophagus, 
the most anterior being formed 
by the nnion of the cerebral 
and buccal ganglia, the pos- 
terior one by the cerebral 
and the aggregated visc'eral 
ganglia, ami the peilal and 
cerebral centres uniting to 
form the central collar. 'Phe 
lesophagus, salivary ducts, 
and i)haryngeal retractors 
l)ass between the cerebral and 
the visceral ganglia and the 
anterior aorta between the 
visceral and the i)edal centres. 
The pedal ganglia are formed 
by a itair of closely ai)posed 
medullary masses united to- 
gether by a broad commissure 
and connected with the cerebral and aggregated visceral ganglia by 
two i)airs of connectives. The i)edal ganglia are placed beneath the 
(esophagus and above the foot, and constitute in part the sub- 
(esophageal ganglionic mass, distriluiting nerve fibres ventrally to the 
locomotor foot and pedal gland and laterally to the neighbouring 
body wall. 
The visceral or i)arieto-splanchnic ganglia are formed by five more 
or less distinctly defined constituents, partially fused when young, but 
Fig. 30S. — Helix aspersa dissected from above to 
show the j^eneral arrangement of the nervous system 
and cephalic retractors. 'I’he liody lias been opened 
to right of the renal organ, the tenl.acles laid open, 
and the crop, buccal retractor and genitalia mainly 
removed, but cut ends shown (after Howes). 
a. auricle and v. ventricle of the heart ; a. a. anterior 
aorta ; buccal ganglia ; />.r. buccal retractor ; c.g. 
cerebral ganglia ; c>\ crop ; c.r. columellar retractor ; 
eye: k. kidney or nephridium ; )ii. mantle; o. om- 
aiatophor ; pg, pedal ganglia ; p,o. pulmonary orifice ; 
p.s. penis sheath ; r. rectum ; s.d. salivary duct ; 
/. anterior tentacle; t.r. tentacular retractors; 
u. ureter ; 7'. vagina; 7'.^’’. visceral ganglia. 
