E. A. Andrews — Anatounj of the Spider Crab. 117 



From eacli side of this oanoHon five lary'e nervous cords (x-xiv 

 fig. 20) pass outward horizontally through the apodemal cells and 

 into the five ambulatory legs where they supply the muscles moving 

 the various joints. These cords are flattened and inclined, those to 

 the first pair of ambulatory legs forward, those to the remainino- 

 ambulatory legs backward. A portion of each cord (x'-xiv') sepa- 

 rates from the rest not far from its origin and continues upward into 

 the apodemal cells as a smaller cord supplying the muscles of the 

 two cells of the segment whose appendage the main part of the cord 

 supplies. The quadrant which is left between the anterior of these 

 five large nervous cords, on either side, and the commissure, is occu- 

 pied by the delicate nerves radiating outward to the mandible, 

 maxillae, and maxillipeds (iv-ix). The most posterior of these is the 

 largest (ix) ; it passes outward into the third maxilliped, and is 

 divided into an upper (ix) and a lower portion (ix') which are 

 separate almost from their origin. The smaller nerve (v^iii) in 

 advance of this is likewise divided into an upper and lower part ; 

 it passes into the second maxilliped. The first maxilliped is sup- 

 plied by a slender nerve (vii) passing forward and outwai'd on the 

 same low plane as those of the other maxillipeds and therefore 

 below the nerve of the second maxilla. This nerve (vr), passing- 

 upward and forward, runs directly above the former and turns 

 outward into the second maxilla between two of tlie apodemal 

 processes. Between this nerve to the second maxilla and the com- 

 missui'e, and close to the latter, the delicate nerves pass forward to 

 the mandible and first maxilla. That to the first maxilla (v) is 

 similar to the nerve to the second maxilla, but nearer to the com- 

 missure ; and it gives off near its origin a delicate bianch which runs 

 forward in close contact with the nerve to the mandible till opposite 

 the first maxilla where it turns outwaid (v') and supplies the muscles 

 of that appendage. The nerve to the mandible (iv) lies very close 

 to the commissure and turns outward into the mandible between the 

 oesophagus and the endostomal plate. A finer nervous filament (it') 

 lies between this last nerve and the commissure, and is continued 

 outward by the side of the oesophagus to the abductor and the 

 adductor muscles of the mandible. 



The thoracic ganglion thus gives origin to a pair of single or 

 double nerves, supplying each of the ten pairs of appendages of the 

 cephalothorax, besides the pair of commissures connecting it with 

 the cc])halic ganglion and the double nerve extending back into the 

 abdomen. In addition to these radiating horizontal neives, a pair 



