KX> 



ZOOLOGY. 



tern of the great sympathetic, &c. is composed of a certain 

 number of small masses of nervous matter, united to each 

 other l.y filaments of communication, and by the same means 

 to the nerves of the cerebro-spinal system. From these 

 ganglions, nerves proceed to numerous vital organs, and are 

 supposed also to follow the course of all the great blood- 

 vessels. 



The ganglions composing this system are arranged in 

 a double column on each side the spine, anteriorly, from the 

 first vertebra to the last ; but many others are scattered through 

 the viscera. They are not found in the limbs. A broad distinc- 

 tion which exists between the cerebro-spinal nerves and the 

 ganglionary is, that the former proceed to the skin, organs 

 of sense, muscles, &c. ; the latter to the vital organs, as the 

 heart, intestines, liver, kidneys, &c. : the former are nerves 

 of relation ; the latter have more a reference to nutrition. 



193. Nervous System of other Animals. In all ani- 

 mals, birds, fishes, and reptiles, the arrangements of the nervous 

 system are much as in man. 



But in the invertebrata it is 

 not so; in these the cerebro- 

 spinal axis seems wanting, and all 

 the nerves of the body seem to 

 reunite in certain ganglions more 

 or less apart from each other 

 (Fig. 60). Finally, in the great 

 divisions of the zoophytes, there 

 remains only a vestige of a rudi- 

 mentary nervous system, and 

 even this seems to be occasionally 

 entirely absent. In speaking of 

 these various groups of animals, 

 the peculiarities here adverted to 

 will be noticed. 



Let us now consider the func- 

 tions of the system. 



194. Sensibility is the faculty 

 to receive impressions, and to 

 have a consciousness of them. It belongs to all animals, but in 

 different degrees. As we ascend in the zoological scale, the sen- 

 sations become more and more varied, the knowledge acquired 

 through them greater, the nervous system more complex. 

 195. In the lowest class of animals, the structure is at 



% ig. 60. Nervous System of 

 an Insect (Carabus of the 

 eardens). 



