Ribs and Secreting Organs. 



FIG. 2. 



Diagram of a vertebra, with its 

 body (5 , rib (7), and breast bone (6). 



is called the thorax ; the region between the thorax 

 and the head is called the neck a very short space 

 in fishes and whales, long 

 in many birds. The part 

 of the vertebral column 

 which projects behind the 

 visceral cavity is named 

 the caudal or tail region, 

 and in it there are usu- 

 ally V-like bony arches, 

 suspended to the lower 

 surface of the vertebral 

 bodies, within which a 

 caudal blood-vessel is pro- 

 tected. 



6. Secreting 1 organs. All vertebrate animals of 

 this division have a solid glandular liver for secreting 

 the bile, an important fluid used in the process of 

 digestion. They have all red blood, the colour de- 

 pending on the presence of certain minute coloured 

 corpuscles. The circulation of the blood is maintained 

 by a muscular heart, which never possesses fewer than 

 two chambers, one of which is for the collection and 

 reception of the blood from the veins, and is called 

 the auricle ; the other, which is named the ventricle, 

 propels the blood into the large blood-vessels or aortic 

 arches, of which there are usually (in some period of 

 life at least) more than three pairs. 



In vertebrates the lining membrane of the mouth 

 (which is named the mucous membrane), clothing the 

 upper and lower jaws, and sometimes the similar 

 membrane over other bones, developes processes or 



