118 E. A. Andreios — Anatonnj of t/ie Spider Crab. 



of ascending nerves (re) arises from the u|)|>er surface of the thoracic 

 ganglion. These nerves arise behind the commissures, in advance 

 of the point of origin of tlie nerves to the chelate feet, and are 

 of about the same diameter as the conmiissures. They extend 

 forward and upward and passing over the edge of the endostomal 

 framework of the gnathites, turn back over the branchial cavity close 

 to the membrane forming its roof as the recurrent cutaneous nerves, 

 subdividing near the apex of that cavity. On turning backward 

 each gives off a large bianch which extends outward over the roof of 

 the efferent canal. 



The nerves supplying the third maxilli])eds (vi, fig. 20), and the 

 first ambulatory legs (vii) coincide in direction at tlieir origin with 

 the arterial branches lying beneath them and supplying the same 

 appendages ; but the nerves to the other appendages do not so 

 coincide, the anterior ones (i-v) arising behind the origins of the 

 corresponding arteries, the posterior ones (viii-xi) arising in front of 

 them. 



The stomato-gastric system comprises the delicate nervous fila- 

 nients arising from the commissures and supplying the muscles of the 

 stomach and cesophagus. There are three of these arising from a 

 slightly swollen portion of each commissure ((/, fig. 20) opposite the 

 oesophagus. The smallest of these arises from the upper surface and 

 l)asses up on the side of the oesophagus. A larger nerve passes down- 

 ward from the lower surface and then forks, the longer fork running 

 forward between the oesophagus and the endostoma towards the 

 labrum. The third nerve passes from the under surface forward, 

 around the oesophagus, just below the commissure, and, sending off 

 two branches upward u])0n the oesophagus and stomach, unites with 

 its fellow on the median line some distance in front of the (esopha- 

 gus (>/). From this union a median nerve passes forward uiuler the 

 cardiac region of tiie stomach till it meets the descending ojihthahuic 

 artery, to the lower or posterior surface of which it closely adheres, 

 and thus passes up <)ver the dorsal surface of the stonuich, supplying 

 the muscles there. From the same ])oint of union a nerve passes 

 downward and soon forks, the branches extending backward on each 

 side of the lower part of the (esophagus. 



