ANATOMY AND PHYSIOLOGY OF ANODONTA FLUVIATILIS. 187 
terior to the first-mentioned nerve is another nerve which bifurcates 
at a short distance from the ganglion, and continues in the muscular 
strata of the foot at an angle of ten degrees to the first-mentioned 
nerve; from this nerve, and also from the others described, proceed 
numerous filaments. From a point about midway between the ends 
proceeds another nerve, which continues almost directly toward the 
ventral margin among the muscular fibres; about midway between 
this nerve and the commissural cord is another nerve (PI. 9, 12, an.), 
which continues directly toward the anterior portion of the animal, 
among the muscular fibres, bifurcating at a short distance from the 
ganglia. From the middle of the dorsal portion (Pl. 9, 12, m. n.) a 
nerve proceeds, continuing posteriorly at right angles to the length of 
the ganglion. The nerve proceeding from the pedal ganglia furnishes 
nerves to the muscles of the body and foot, and to the viscera. 
The posterior ganglia (Pl. 9, 12, p.s. g.) are situated immediately 
below the posterior adductor muscle, and are so closely apposed 
as to present the appearance of a single bilobate ganglion, The 
bilobate appearance is more apparent than that of the cerebral 
ganglia, but they are much more closely united than the pedal gang- 
lia; each ganglion is two millimetres long and one and one-half mulli- 
metres wide, and the inner margin is joined to its fellow throughout the 
entire length. From the anterior portion proceed the commissural cords 
(Pl. 9,12, p. s. ¢.), connecting the posterior and cerebral ganglia. 
From the anterior angles of the ganglia (Pl. 9, 12, g. n.) proceeds a 
peripheral nerve, which for a short distance continues parallel with 
the commissural cord, then curving away from that cord turns quite 
abruptly backward, continuing along the junction of the exterior 
lamelle of the inner gills and the inner lamelle of the outer gills, 
branches entering the gills. From the posterior portion of the gang- 
lia a very large nerve takes its origin, the diameter of which is equal 
to three times the diameter of the commissural cord. (PI. 9,12, p. n.) 
This nerve at first continues directly toward the posterior portion of the 
animal, branching at the distance of about seven millimetres from 
the ganglia (PI. 9,12, p.m.n.). The branch entering the mantle 
is first directed toward the ventral portion, gradually curving and 
becoming parallel with the ventral portion, and having frequent 
branches, which continue into the muscular portion of the mantle. 
This nerve is slightly smaller than the commissural cord, Almost im- 
mediately after this branch leaves the large nerve, that nerve again 
branches, the larger portion continuing toward the rudimentary 
branchial siphon, and its branches supplying that portion of the man- 
tle with nerves (Pl. 9,12,b.n.). Likewise the smaller portion proceeds 
toward the rudimentary exhalent siphon. In addition to these princi- 
