Anatomy and Physiology of Anodonta Fluyiatilis. 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 (PL 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 (PI. 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 (PI. 9, 12, p. s. g.) are situated immediately 

 below the posterior adductor muscle, and are so close] y 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 milli- 

 metres wide, and the inner margin is joined to itsfellow throughout the 

 entire length. From the anterior portion proceed the commissural cords 

 (PI. 9, 12, p. s. a), 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 

 lamellae of the inner gills and the inner lamellae 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. (PL 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 (PL 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- 



