490 OF THE NERVOUS SYSTEM AND ITS ACTIONS. 



the brain, which constitute (as we shall presently find) its fundamental 

 portion, and with which all the cephalic nerves are immediately con- 

 nected. 



866. When we direct our attention to the nervous system of the 

 Vertebrated series, we perceive that it differs from that of the Inver- 

 tebrated classes we have been considering, in two remarkable features. 

 In these last, it has seemed but as a mere appendage to the rest of 

 the system, designed to bring its several parts into more advantageous 

 relation. On the other hand, in the Vertebrata, the whole structure 

 appears subservient to it, and designed but to carry its purposes into 

 operation. Again, in the Invertebrata, we do not find any special 

 adaptation of the organs of support for the protection of the Nervous 

 System ; for it is either enclosed, with the other soft parts of the body, 

 in one general hard tegument, as in the Star-fish and other Echinoder- 

 mata, and in Insects, Crustacea, and other Articulata ; or it receives a 

 still more imperfect protection, or even none at all, as in the Mollusca. 

 Now in the Vertebrata, we find a special and complex bony apparatus, 

 adapted in the most .perfect manner for the protection of the Nervous 

 system ; and it is, in fact, the possession of a jointed spinal column, 

 and of its cranial expansion, which best characterizes the group. 



867. The Nervous System of Vertebrata is not merely remarkable 

 for its high development, relatively to the remainder of the structure : 

 it is also distinguished by the possession of parts, to which we have 

 nothing analogous in the lower tribes ; and by the mode in which these 

 are concentrated and combined, so as to form one continuous mass, 

 instead of consisting of a series of scattered ganglia. The chief parts 

 which are newly introduced (so to speak) in this sub-kingdom, are the 

 Cerebral Hemispheres and Cerebellum ; of which there are no traces 

 whatever in the lower Articulata and Mollusca, and but very uncertain 

 representations in the highest. These are superimposed, as it were, 

 upon the cephalic ganglia connected with the organs of special sense, 

 and upon the cords that connect them with the first ganglion of the 

 trunk. Again, we find that the locomotive ganglia, which formed the 

 long knotted cord of the Articulata, are united with the centres of the 

 respiratory system, and with those of the stomato-gastric system, to 

 form one continuous tract, which commences anteriorly from the gan- 

 glia of special sense, and runs backwards* without interruption, in the 

 canal of the Vertebral column, forming the spinal cord. This is a con- 

 tinuous instead of an interrupted ganglionic mass ; it is composed of 

 two lateral halves, precisely similar to each other ; and each of these 

 consists of two parts, as distinct from each other as the two tracts in 

 the ventral cord of the Articulata, namely, a fibrous structure, which 

 connects every part of it with the Encephalon (or collection of nervous 

 masses within the cranium), and which also serves to connect together 

 the different parts of the cord itself, and a vesicular portion, which 

 forms the proper centre of the greater part, if not the whole, of the 

 fibres entering into the roots of those nerves. The anterior portion of 

 the Spinal cord, which is prolonged into the cranium, and comes into 



* When we speak of the Vertebrata generally, their bodies are of course supposed to 

 be in a horizontal position, not vertical, as in Man. 



