NERVOUS SYSTEM, 



223 



which invests the cerebral organs is occupied by the 

 soft transparent semifluid cellular tissue of the arach- 

 noid coat which passes down likewise through the ver- 

 tebral canal, enveloping the spinal chord. The spinal 

 chord is nearly equal in its development throughout 

 the vertebral column, even in many of the anguilliform 

 osseous fishes, from the smallness of the arms and legs 

 not requiring those enlargements which we observe in 

 most higher animals, where the nerves of larger and 

 more powerful extremities are given off. In species 

 which have the arms of great magnitude, as rays and 

 flying-fishes, there is a proportionate development of 

 the upper enlargements of the spinal chord. The num- 

 ber and the extent of these enlargements of the spinal 

 chord in fishes corresponds with that of the members 

 developed from the periphery of the trunk. In the 

 trigla (Fig. 95. C,) where the pectoral fins are of great 

 size, a series of ganglionic enlargements (95. C. b. ,) 



FIG. 95. 



of the spinal chord (a) are observed at its upper part, 

 which corresponds in number with the number of the 

 large detached rays of the pectoral fins presented by 

 the different species, trigla cuculus having five enlarge- 

 ments and five detached rays, and the trigla lyra (95, C.) 



