244 SUPPLEMENT 



the assemblage of the coiuposite eyes. From the lower face 

 of the brain, originate four other nerves, which go to the an- 

 tennae, and which give out some threads to the neighbouring 

 parts. From its posterior edge, spring two very elongated 

 nervous cords, which comprehend the CESophagus between 

 them, and unite imderneath, in an enlargement or medial 

 ganglion, and which give out towards the middle of their 

 length, a thick nerve which repairs to the mandibles and to 

 their muscles. The ganglion inferior to the oesophagus, fur- 

 nishes the nerves which proceed to the jaws, and to the jaw- 

 feet." 



" In the asfaci, and the other macrourous decapod Crus- 

 tacea, the two cords remain inter-approximated throughout 

 the entire length of the body, and form there five successive 

 ganglia, placed between the articulations of the five pairs of 

 feet. Each foot receives a nerve from the ganglion, which 

 corresponds to it, and this nerve penetrates as far as its 

 extremity. That of the claw, or forceps, is the thickest. 

 The medullary cords, when arrived at the tail, unite so in- 

 timately that it is no longer possible to distinguish them. 

 They form then six ganglia, of which the first five furnish 

 each two pairs of nerves. The last produces four, which are 

 distributed in radii to the scaly fins that terminate the tail." 

 In the crabs all the anterior part of the nervous system is the 

 same, but the two oesophageal cords are united a little more 

 backwards than in the astaci. " They are," continues the 

 Bai'on, " in the middle of the thorax, and there commences 

 a medulla, shaped like an oval ring, grooved in the middle, 

 and eight times larger than the brain. From the circum- 

 ference of this ring spring the nerves which proceed to the 

 different parts. It furnishes six nerves on each side for the 

 jaws, and the five feet, and there is an odd one which comes' 

 from the posterior part, and repairs to the tail. It represents, 

 as it were, the ordinary knotty cord ; but its ganglia, if it have 



