232 MESSRS. HANCOCK AND EMBLETON ON THE ANATOMY OF DORIS. 
eleventh and twelfth nerves arise also from these centres, and are distributed to the 
sides of the body between the mantle and the foot. 
The lateral or pedial ganglia lie on a plane rather beneath the others, with both of 
which they are connected, and in shape and size are like the branchial. Three large 
nerves, the thirteenth, fourteenth and fifteenth pairs, are given off from these centres, 
and supply the whole foot. 
The single supra-oesophageal or visceral ganglion* is round, and about the size of 
the olfactory ; it is sessile on the under surface of the anterior border of the right 
branchial ganglion, where this is in contact with the pedial. The nerves g, h, i, j 
issue from this ganglion ; (g) the first in origin passes down by the side of the aorta, 
to which it gives branches ; one of these has a small ganglion (n) in its course ; the 
other, the larger, passes further on, and ends in two or three ganglia (p) placed at 
the root of the aorta, which send branches to the pericardium and heart. The trunk 
of the nerve passes down towards the branchiae, and in so doing, gives off next 
another branch to the systemic heart, and then a large offset to the portal heart ; 
after this the nerve comes into connection with the branchial ganglia and plexus {q) 
of the sympathetic system, and communicates with the renal plexus (?;), apparently a 
dependence of the former or branchial. The next in order (h) runs backwards to 
the right side towards the base of the bag of the penis, where it merges into the 
principal sympathetic ganglion of the generative organs. The third nerve (/), 
smaller than the last, rims beneath the organs of reproduction and the stomach, and 
in its course distributes two or three branches to the mucuS'-gland, joining an open 
plexus {s), with a few small ganglia situated on that organ ; the nerve then inclines 
towards the left side, presenting a small ganglionic swelling in its course ; and shortly 
afterwards passes into the largest ganglion (t) of the gastro-hepatic plexus, that 
which receives the right par vagum nerve. The last nerve (j) runs straight back- 
wards to the vicinity of the branchiae, and after giving off two or three twigs appa- 
rently to the intestinal plexus (^e), as it passes under the intestine, terminates in a small 
ganglion closely connected with the larger one, into which nerve (g) runs, both of 
these ganglia belonging to the branchial plexus (q). 
We now come to the third, or posterior, or great oesophageal collar (m) ; it is 
stouter, more closely invests the esophagus than the other two, and is composed of 
three parallel cords, two of which are attached to the under surface of the peilial 
ganglia ; the third has one end in connection with the left branchial, and the other 
with the visceral ganglion. 
The infra-oesophageal ganglia'i~ are two pairs symmetrically disposed on the buccal 
mass ; the larger or buccal, as we have seen, are connected by means of a collar with 
the cerebroid. They are elliptical, and are united by a short commissure. They 
give off laterally, and in union with the collar, two pairs of nerves, the sixteenth and 
seventeenth, which are distributed to the buccal mass. The eighteenth is a small 
* Plate XVII. fig. 1. t Plate XVI. fig. 8. 
