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 



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, C Sj 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. 



Lower tube or cavity 



containing lungs, 

 heart, stomach, etc. 



FIG. 189. A vertebra and a pair of ribs, 

 from a cat. CS, upper cavity, con- 

 taining cerebro-spinal cord ; and low- 

 er, containing lungs, etc. 



