NERVOUS SYSTEM OF VERTEBRATA. 265 



the Organic functions, are placed under the control of the Will, guided by the 

 reasoning faculties. This is especially true of the locomotive organs, whose 

 rellex actions are entirely governed by the will ; being only distinguishable as 

 such, when, from peculiar states of the system, the immediate influence of 

 the controlling power is suspended. We shall find ground to believe, that 

 the exercise of the Reasoning faculties, and the resulting operations of the 

 Will, take place through the instrumentality of another division of the nervous 

 centres ; to which there is nothing distinctly analogous among the Inverte- 

 brata ; but which seems to bear a constant proportion in size and importance, 

 among Vertebrated animals, to the development of the Intelligence and its 

 influence on the movements of the body : namely, the Cerebral ganglion. 



338. There is another aspect, however, under which we are to consider 

 the Nervous System ; and this becomes more important in the highest division 

 of the Animal kingdom, on which we are now about to dwell. We have 

 hitherto spoken only of its influence on the contractile properties of the tis- 

 sues, to which it is distributed. It has, however, an important and direct 

 connection with the purely organic functions of Nutrition and Secretion; and 

 we shall see reason to regard it as the means, not only of placing the animal 

 in relation with the external world, but of harmonizing and controlling the 

 organic changes taking place in its own structure, and of bringing these under 

 the influence of particular mental conditions. The opinion is entertained by 

 many, that all the Organic Functions are dependent upon the innervation, 

 supplied to them by the system of nerves, which has been termed Sympathetic 

 or visceral. It is incumbent, however, on those who uphold the necessity of 

 this nervous power, to prove it definitively; since all analogy leads to an 

 opposite conclusion. We may regard the capability of separating a particular 

 secretion from the blood, as a peculiar property inherent in the glandular cells, 

 just as contractility is the inherent property of muscular fibre. But as the 

 peculiar arrangement of the excitable and contractile tissues in Animals, 

 requires a nervous system to act as a conductor between them, and to blend 

 their actions ; so may the complicated Organic functions of Animals require 

 to be harmonized and kept in sympathy with each other, by some mode of 

 communication more direct and certain than that afforded by the circulating 

 system, which is their bond of union in Plants. We have seen, in the fore- 

 going sketch, that the Visceral system does not exist in a distinct form in the 

 lower classes of Invertebrated animals ; and also that the nervous system of 

 these classes cannot, as a whole, be compared with it, although it may be 

 regarded as containing some rudiments of it. As the divisions of this system 

 become more evident, however, and the organic functions more complicated, 

 some appearance of a separate Sympathetic system presents itself; but this is 

 never so distinct as in Vertebrata. Hence, it may fairly be inferred that, as 

 the Sympathetic system is not developed in proportion to the predominant 

 activity of the functions of organic life (which is so remarkable in the Mol- 

 lusca when contrasted with the Articulata), but in proportion to the develop- 

 ment of the higher divisions of the nervous system, its office is not to 

 contribute to these functions anything essential to their performance ; but 

 rather to exercise that general control over them which becomes the more 

 necessary as they become more independent of one another; and to bring 

 them into relation with the system of Animal life. 



3. Nervous System of Vertebrata. 



339. When we direct our attention to the Nervous System of the Verte- 

 brated classes, we are immediately struck by two remarkable differences which 

 its condition presents, from that under which we have seen it to exist in the 



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