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 
Yertebrata 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 Yertebrata, 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 Yerte- 
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 l , 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 , 
