INTERNAL ANATOMY. 341 
fine nerves to the superficial muscles of the bulb in this region, penetrates below 
the surface and continues forward to the ventral part of the anterior end of the 
bulb, ramifying there to it and to the mouth-tube. 
The third buccal nerve, 6 3, arises very close behind the second nerve and 
passes upward, parallel to the proximal portion of the salivary gland. It gives 
off a delicate branch to the superficial circular muscles of the posterior portion 
of the bulb, and to the duct of the salivary gland, and then divides into two 
main rami, the anterior one of which passes forward and upward to the super- 
ficial dorsal muscles of the bulb, while the posterior one passes dorsally and 
ramifies in the thin dorsal wall of the bulb directly beneath the cerebral ganglia. 
The fourth buccal nerve, b4, arises from the outer posterior margin of the 
buccal ganglion, and bifurcates into two equal rami before emerging from the 
capsule. The more anterior of these, 4a, curves upward along the inner margin 
of the salivary gland, which it closely follows to the entrance of its duct into the 
bulb, giving off numerous fine branches to the duct, and to the dorsal wall of 
the anterior end of the oesophagus, below the cerebral ganglion complex. The 
posterior ramus, 4b, passes backward along the oesophageal wall, giving off a 
delicate branch to the salivary gland, and another to the anterior portion of 
the tube; the main trunk continuing along the side of the oesophagus through- 
out its whole extent, sending off numerous branches to it at intervals, which, 
anastomosing with those of its fellow of the opposite side, form a rich plexus 
in the oesophageal wall. Reaching the ingluvies the two trunks are pro- 
longed over its wall to its junction with the thick-walled triturating gastric divi- 
sion. Here there is found a ring of nervous tissue surrounding the whole canal, 
in which the two nerves merge. From this nerve-ring numerous delicate nerves 
are given off to the gastric wall, forming a rich plexus, while four larger nerves 
approximately equidistant from each other, pass backward along the wall of 
the first triturating stomach. Beyond the posterior boundary of the first 
triturating division, branches are given off laterally from each of these, which 
anastomose mutually and form a second more irregular nerve-ring in the ante- 
rior wall of the second triturating stomach. From this second ring numerous 
nerves pass backward throughout the whole length of the intestine, giving off 
abundant irregular branches to its wall, which unite in extensive plexuses. A 
stronger laterally placed trunk on either side, while often obscure, still may 
usually be made out, as an indication of the primitive bilateral arrangement 
of the nerve distribution. 
Parieto-visceral ganglia—The parieto-visceral ganglion complex is situated 
