1334 



CRUSTACEA. 



The remaining pair of nerves (c) arise from the anterior angles of the 

 ganglion, and pass to the antennae ; they are one-half larger than any 

 other in the body. Near their origin, they give off exteriorly a slender 

 branch, which continues nearly parallel with the main nerve, and 

 passes to the muscles of the antennae. Without farther branching, 

 they extend in nearly a straight line to the base of the antennae, 

 where they subdivide into four large branches, which are distributed 

 to the fleshy papillae (fig. r). Two nerves from the posterior branch 

 run along the muscles, and are continued into the terminal joints, one 

 to each of the two terminating sets of setae. The antennae are so 

 abundantly furnished with nerves, that they must be the seat of an 

 important sense. The sense of touch is the only one for which their 

 peculiar form and their delicate papillae appear adapted. 



The thoracic ganglion, which is composed of all the thoracic and 

 abdominal ganglions united, has a cordate form, and is somewhat 

 larger than the cephalic. This ganglion gives off seven pairs of nerves 

 in front and laterally, and two pairs behind, besides a central nerve 

 or cord. 



The first two pairs originate at the centre of the anterior margin 

 (d, e, fig. s). The inner is quite slender, and appears to enter the 

 mouth each side of the oesophagus. The second has twice the dia- 

 meter of the first; it curves more outward, and is supposed to go to 

 the mandibles and their muscles. These nerves pass under the buccal 

 mass, and cannot be traced while it is in its natural position. They 

 invariably appear broken off when the buccal mass is removed ; and 

 sometimes after detaching it, a nerve equal in size to the first, has 

 been seen entering the mouth near the oesophagus, as above stated. 

 These facts have been deemed sufficient to authorize the above opi- 

 nion respecting the destination of these nerves. 



The third pair (f, fig. s) arise from the anterior angle of the gan- 

 glion. They give out a branch exteriorly to the muscles of the first 

 pair of legs, and afterwards continue to these organs, and pass into 

 the terminal joints after giving a branch to the basal. 



The fourth pair (g) arise just posterior to the last, and are distri- 

 buted to the outer teguments. They afford a branch near their 

 origin, which probably passes to the rudimentary legs : soon after 

 they divide into two parts ; one branch passes outward and a little 



