NERVOUS SYSTEM OF VERTEBRATA. 87 
resembling those of the back, but simpler in their form, and 
“not possessing a cavity for the spinal cord. We commonly 
find that in those animals in which the skull is very large, 
the tail is short; and that where the tail is very long or 
| powerful, the head is small. Thus in man and in the apes, 
the head is large, and there is no 
external appearance of a tail ; but there 
are some very imperfect vertebre at the 
lower end of the spinal column, which 
constitute the rudiment of it. In the 
long-tailed monkeys and in the kan- 
garoo (whose tail is like a third hind- 
leg), the head is comparatively small. 
But this rule does not hold good uni- 
_ -versally. 
\ 72. The Nervous system of Verte- 
_ brated animals consists of a Brain and 
Spinal Cord-(fig. 28), which are lodged 
- within the skull and vertebral column ; 
and of nervous trunks proceeding from 
these, which are distributed to all parts 
of the body. The Brain is not (as 
- commonly reputed) a single organ, but 
_ is composed of a number of ganglionic 
| masses, differing considerably in their 
functions. Thus each of the nerves 
of special sense (smell, sight, hearing, 
and taste) has its own proper centre ; 
and there is another of considerable 
size, which seems to perform the same 
office in regard to common sensation. 
These are found in Vertebrata generally ; 
-and their proportionate size corresponds 
with the relative’ development and ac- 
“tivity of the several organs of sense 
with which they are connected. The _ 
“bulk of the brain of Man, however, is "##-26>Beats xp Spivat 
“made up by two large masses of nervous 
“matter, which are known as the Cerebral Hemispheres; these, 
“as will be shown hereafter (chap. x.), are so small in the brains 
of Fishes as to be scarcely distinguishable ; and their relative size 
= 
