18 NATURAL HISTORY. 
motion among the vertebre; while in the body of the 
_animal the motion between them is slight. 
9. In the snake tribe of Vertebrates the vertebre are 
very numerous, and the motion between them is as free 
as in the tails of quadrupeds. Some species have over 
three hundred, while in man there are only twenty-four. 
10. The skeletons of the different kinds of animals that 
[have mentioned differ from each other in many respects. 
For example, the fish has nothing in its skeleton that is 
like the bones of the extremities in man, and that of the 
serpent is composed merely of vertebree, with very short 
Ray ribs. There are some fishes that have 
no ribs. In the turtle, as you see in Fig. 
6, the ribs spread out into broad plates, 
which, joined together, make its upper 
covering, termed the carapace. 
11. While the differences are of ex- 
treme variety, the skeletons of all these 
< animals agree in one thing—in having a 
- vertebral column. They are, therefore, 
classed together as vertebrate animals. 
12. Connected with this grand char- 
acteristic of this division of the animal 
kingdom there is another, viz., the ar- 
rangement of the great central organs 
of the nervous system. ‘These are in- 
closed in the skull and vertebral column. 
The brain is in the skull, and the verte- 
bree contain the spinal marrow, which 
extends from the brain through the 
length of the body. Each vertebra has 
a round opening through it, as you see 
in Fig. 2. When, therefore, all the ver- 
tebree are joined together, there is a 
tube-like passage through the column. 
| _ In this lies the spmal marrow, or cord, 
Fae eo ernn me * as itis often called. In Fig. 7 you have 
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