88 NERVOUS SYSTEM OF VERTEBRATA. 



and complexity of structure increase as we ascend the scale, 

 in pretty close accordance with the increase of the intelligence 

 or reasoning faculty. There is also another large nervous 

 mass, called the Cerebellum ; the function of which seems to 

 consist in the regulation of the more complex movements. 

 The Spinal Cord is made up of a longitudinal succession of 

 independent centres, of which one corresponds with each of 

 the vertebral segments of the body. 



73. The distinguishing feature of the Nervous system in 

 Vertebrata is, that its several centres are thus united into one 

 large mass, instead of forming a number of separate small 

 masses or ganglia, as we shall find that they do in the lower 

 classes of animals : and that it is inclosed in the bony casing 

 which has been described as peculiarly destined for its pro- 

 tection, instead of being enveloped with all the other organs 

 in a hard covering, as in the Lobster, or of being entirely 

 destitute of protection, as in the Slug. That it should receive 

 this peculiar protection is quite necessary, in consequence of 

 the much higher development which it attains, and the much 

 greater importance which it possesses, in this division of the 

 animal kingdom, than in any other. In all but the very 

 lowest Vertebrata, all five kinds of sensation exist ; namely, 

 sight, hearing, smell, taste, and touch. We find in this group 

 more intelligence than in any other ; that is to say, the animals 

 composing it act more with a designed adaptation of means to 

 ends ; instead of being impelled by a blind instinct to perform 

 actions of whose objects they are not aware. And we find, by 

 observing and comparing the structure and actions of the dif- 

 ferent groups, that the intelligence gains upon the instinct, as 

 we ascend from the lowest Fishes towards Man, in whom the 

 intelligence is at its highest ; whilst we observe a similar 

 increase in the proportion which the brain bears to the rest 

 of the nervous system. Hence we conclude, that the brain is 

 the organ of intelligence, or of the reasoning faculties. 



74. The general arrangement of the other organs in Verte- 

 brated animals, is shown in fig. 29. At m is seen the mouth, 

 forming the entrance to the digestive cavity, of which the 

 termination is at the opposite extremity of the body ; i, i, is 

 the intestinal canal, and I, the liver : these organs occupy the 

 part of the body which is called the abdomen or belly. The 

 mouth also opens, however, into the windpipe, or trachea, t, 



