SEA MUSSEL MYTILUS EDULIS. 



171 



nective continues backward and around the anterior retractor muscle to its dorsal wall 

 and terminates in the pedal ganglion (fig. 159, CPC). The cerebrovisceral connective 

 at the point of bifurcation with the cerebropedal connective turns upward and con- 

 tinues in a posterior direction across the lateral surfaces of the posterior retractor muscles 

 to its point of termination in the visceral ganglion (fig. 159, CVC). Along its course 

 several delicate nerve branches are given off which go to the liver, intestines, genital 

 glands, and kidney. Of these the last branch forward, the anterior renal nerve (fig. 163, 

 ARN, p. 175) is the most prominent. The otocyst nerve is a very fine fiber that arises 

 from the cerebropedal connective at its junction with the cerebrovisceral connective 

 and continues a short distance backward to the otocyst (fig. 163, OtN). 



DRBN CVC DPN PPN 



\ I PPdN • 



BAPN 

 APN CPC 



PdG\ vhbn 

 PdN 



PRB 



159 



Mes 



YG BrN 



Fig. 159. — Ventrolateral view of the nervous system in a transparent total preparation of a mussel 10.5 mm. long, separated 

 from the shell, mantle and gills removed from one side, and a portion of foot cut ofT. Fixed in strong Fleniming fluid, exposed 

 in 70 per cent alcohol to strong sunlight, dehydrated in alcohol and cleared in benzol and wintergreen oil. X 15. A PN, anterior 

 pallial nerve; BAPN, branch of anterior pallial nerve; BrN , branchial nerve, BuN, buccal nerve; CC, cerebral commissure; 

 CG, cerebral ganglion; CPC, cerebropedal commissure; CVC, cerebrovisceral commissure; DPN, dorsal pallial nerve; DRBN, 

 dorsal retractor byssus nerve; L, liver; Mes, mesosoma; Mih, mouth; PdC, pedal ganglion; PdN , pedal nerve; PDPN , posterior 

 dorsal pallial nerve; PPdN , posterior pedal nerve; PPN , posterior pallial nerve; PRB, posterior retractor muscle of byssus; 

 PVPN, posterior ventral pallial nerve; S.V. syphonal nerve; VC, visceral commissure; VG, visceral ganglion; VRBN, ventral 

 retractor byssus nerve. 



The buccal nerve is a relatively fine fiber which arises from the anterior end of the 

 cerebral ganglion and runs forward to supply the labial palps (fig. 159, BuN). Branches 

 of the nerve enter the palps and run along the smooth edge as a loose bundle of fibrils 

 from which single fibers run out laterally across the palp and penetrate the transverse 

 ridges (fig. 160, BuN, p. 173). 



The optic nerve arises from the cerebral ganglion just posterior to the buccal nerve 

 as a very fine fiber and runs in an anterio-latero-dorsal course to the eye at the base 

 of the first inner branchial filament (fig. 163, OpN, p. 175). 



A few very fine nerves that are distributed about the mouth region are also given 

 off from the median sides of the cerebral ganglion and from the cerebral commissure. 



