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posterior to the mantle cavity. They can be seen from 

 the exterior, without any dissection, under the epithelium 

 of the area between mantle, digestive gland and 

 columellar muscle. The other part of the visceral loop 

 connecting the visceral ganglia with the supra-intestinal 

 ganglion is by no means easy to follow, for it lies under 

 the superficial muscles of the left wall of the body cavity. 

 It leaves the wall near the point of entrance of the two 

 left pallial nerves (figs. 41 and 42, pall n."), and runs 

 along with them to the supra-intestinal ganglion. The 

 three nerves have thus to cross over the alimentary canal 

 and gland of Leiblein. Of the usual figure of eight 

 formed by the visceral commissure, only the lower, 

 posterior, loop is of any extent. 



The two large left pallial nerves arise in the supra- 

 intestinal ganglion, and passing over to the left side, 

 plunge through the body wall. They are extremely 

 close together at first, and form one thick band. On 

 reaching the mantle they proceed to divide. The most 

 anterior nerve innervates the osphradium. In addition 

 to this, it gives rise to some twigs which, by means of 

 their anastomosis with the siphonal nerve, set up the 

 zygoneural connection already mentioned as existing on 

 the left side. Both the anterior and posterior pallial 

 nerves from the supra-intestinal ganglion take part in 

 the innervation of the gills. 



An important nerve arises from the sub-intestinal 

 part of the commissure itself, just at the posterior end of 

 the perivisceral cavity. It runs outwards, underneath 

 the vas deferens in the male (fig. 41, com. n.) to the 

 rectum and mucous gland. 



The Visceral Ganglia are two in number. Of these 

 the right is much larger than the left, and gives origin 

 to most of the nerves. The principal nerves are the 



