CHAPTER IX. 
NINTH BRANCH OF ANIMALS. 
BACKBONED ANIMALS (Vertebrata). 
General Characteristics.—The Vertebrates are distin- 
guished by the possession of a backbone, or vertebra, but 
Lower tube or cavity, 
containing lungs, 
heart, stomach, etc. 
Fic. 189.—A vertebra and a pair of ribs, 
from a cat. C.S, upper cavity, con- 
taining cerebro-spinal cord; and low- 
er, containing lungs, etc. 
the fundamental dis- 
tinction between them 
and the preceding forms 
lies in the fact that the 
body is divided into two 
tubes (Fig. 189)— the 
upper, CS, containing 
the nervous cord, and 
the lower the heart, di- 
gestive organs, etc. The 
eyes, ears, and nostrils 
are two in number, and 
are placed in the same 
relative position in all. 
The eyes have movable 
lids; the mouth opens 
transversely ; the lower 
jaw is on the under part 
of the head, and moves 
up and down, instead of opening sidewise, as in the insects 
and crustaceans. The jaws are armed with teeth. The 
blood, except in the lancelet, is red, 
