888 ANATOMY AND DEVELOPMENT 



cesophageal commissures. On the ventral surface of each, rather 

 behind the level of the eye, is placed a very peculiar pro- 

 tuberance (fig. 22 d], of which I shall say more in dealing with 

 the histology of the nervous system. 



A number of nerves arise from the supra-cesophageal ganglia, 

 mainly from their dorsal surface. 



In front are the immense antennary nerves extending along 

 the whole length of each antenna, and giving off numerous 

 lateral twigs to the sense organs. Near the origin of the an- 

 tennary nerves, and rather on the dorsal surface, there spring 

 a few small twigs, which pass to the skin, and are presumably 

 sensory. The largest of them is shewn in PL 50, fig. 19 A. 

 About one-third of the way back the two large optic nerves take 

 their origin, also arising laterally, but rather from the dorsal 

 surface (PL 50, fig. 19 D and E). Each of them joins a large 

 ganglionic mass placed immediately behind the retina. Nearly 

 on a level with the optic nerves and slightly nearer the middle 

 dorsal line a pair of small nerves (fig. 19 D) spring from the 

 brain and pass upwards, while nearly in the same line with the 

 optic nerves and a little behind them a larger pair of nerves take 

 their origin. 



Behind all these nerves there arises from the line of suture 

 between the two supra-cesophageal ganglia a large median nerve 

 which appears to supply the integument of the dorsal part of 

 the head (PL 48, fig. 8 ; PL 49, figs. 1 1 14 dn}. 



Sympathetic System. In addition to the nerves just de- 

 scribed there are two very important nerves which arise near 

 the median ventral line, close to the hind end of the supra- 

 cesophageal ganglia. The origin of these two nerves is shewn 

 in the surface view (fig. 22 sy, and in section in fig. 11). They 

 at first tend somewhat forwards and pass into the muscles near 

 the epithelium lining the groove on each side of the tongue. 

 Here they suddenly bend backwards again and follow the 

 grooves into the pharynx. 



The two grooves are continuous with the two dorsal angles 

 of the pharynx ; and embedded in the muscles of the pharynx, 

 in juxtaposition with the epithelium, these two nerves may 

 easily be traced in sections. They pass backwards the whole 

 length of the pharynx till the latter joins the oesophagus. 



