262 DR. A. RATTRAY ON THE ANATOMY, PHYSIOLOGY, 
described, joins the buccal ganglion, while the smaller runs onward, subdivides, and is 
lost in the tissues of and near the mouth. 
b. The cephalo-pedal (Plate XLITI. figs. 1 & 8, y), which exceed the former in size, 
and, next to the optic nerves, are the largest in the body, arise posteriorly from the 
cephalie ganglion internal to the optic, run back towards the pedal ganglion on either 
side and above the cesophagus, but often widely apart, giving off branches to the mus- 
cular coat, tunic, &c. 
Besides the purely sensory nerves and those of intercommunication, the cephalic gives 
smaller twigs to the tissues in its vicinity, e. y. the cesophagus, aorta, muscular and 
outer tunics, sclerotic, &c. (Plate XLIII. fig. 8), which form a kind of plexus round the 
ganglion. 
9rd. The pedal ganglion (Plate XLIII. fig. 1, 4), next in size to the cephalic, is found, 
as its name implies, near the base of the ventral fin, the representative, according to 
Huxley, of the anterior division of the foot or propodium of the typical gasteropods, and 
consists of two oval lobes, prolonged anteriorly and united centrally by a thick com- 
missure. As a whole it is more globular than the cephalic, like which its internal 
structure consists of nucleated cells in a general envelope prolonged as nerve-sheaths 
(Plate XLIII. fig. 7). It sends off intercommunicating branches to the ganglia above 
and below, and also supplies the neighbouring tissues. 
The important cephalo-pedal nerves have already been described. 
The pedo-branchial cords (Plate XLIII. figs. 1 & 4, o), also large, spring from the right 
and left lobes, run backward, above and on either side of the alimentary canal, pursue 
a wavy course, giving off filaments as they pass to the lower part of the cesophagus, 
stomach, &e., till, in front of the branchial nucleus, they suddenly bend (fig. ) nearly at 
right angles, to embrace the intestinal canal and join the branchial ganglion. | 
Smaller nerves are distributed, first, to the foot, the external coat, and predominant 
muscular tissue, all of which are well supplied; second, to the muscular and hyaloid 
coats; and, third, to the stomach, cesophagus, and male generative organs (fig. 4). 
4th. The branchial ganglion (Plate XLIII. fig. 4, P), smaller than either of the former, 
and more like the buceal in size, lies below the posterior end of the intestinal canal, in 
front of the visceral nucleus and heart. Tt is joined in front by the two pedo-branchial 
eords (figs. 1 & 4, o), and gives off the following. One long filament (q) runs along the 
upper aspect of the intestinal canal to be distributed on the cesophagus and stomachic 
dilatation, besides giving off twigs to the male generative organs when present here. 
Two others (7) run upwards, embrace the lower part of the intestinal canal, and join 
a plexus (x) to be presently described. Arising from one or both of these a long 
thread (7^) runs along the abdomen close to the muscular coat, to join with others sent: 
from the pedal ganglion. Posteriorly it supplies the muscular and transparent coats and 
the organs constituting the branchial nucleus (£)—namely, the stomach, rectum, liver, 
heart, branchial apparatus, male and female generative organs. What may be termed 
the “caudal plexus,” just alluded to (u), lies above the branchial nucleus near the dorsal 
surface. More or less quadrilateral, it is joined at either corner in front by a cord from 
each lobe of the branchial ganglion (»), and one from the pedo-branchial nerves of inter- 
