155 



abdominal ganglia. It passes backward along the median 

 line of the " sella turcica" and along the ventral region 

 of the abdomen. Small nerves are given off to each 

 somite of the abdomen. 



According to Jolyet and Yiallanes,* the centres of the 

 moderator and accelerator nerves of the heart are in the 

 anterior part of the ventral nerve mass. The cardiac 

 nerve of the Macrura does hot appear to be present in the 

 crabs. 



The Stoniatogastric System. 



This consists mainly of nerves arising from the 

 paroesophageal ganglia. These nerves fuse to form the 

 stornatogastric nerve, which supplies the anterior and 

 dorsal regions of the fore-gnt. There is also the postero- 

 lateral nerve arising behind each paroesophageal ganglion. 



There are two main nerves arising from each 

 paroesophageal ganglion. These pass below the com- 

 missure, and, passing forward, they fuse with each other 

 and with the similar nerves of the other side to form the 

 main stomatogastric nerve. The ventral nerve (st. i.) 

 arises from the outer side of the ganglion, and 

 immediately passes below the lateral dilator muscle of the * 



oesophagus, to which it gives small branches. It passes 

 below the commissure and innervates the anterior dilator 

 muscles of the oesophagus. It then turns upward and 

 fuses with the similar nerve of the other side and with the 

 dorsal nerve. The latter nerve (st. s.) arises from the 

 anterior and outer side of the paroesophageal ganglion. 

 It passes immediately below the commissure, and gives oft' 

 a small nerve to the anterior walls of the oesophagus. In 

 the median line it fuses with the corresponding nerve of 

 the opposite side, and also with the ventral nerve. 



The stomatogastric nerve (st. n.} is formed by the 



* Jolyet et Viallanes. Comptes Rend us, CXIV (1892), p. 189. 



