Mammalia. 



251 



The Circulation of Blood in the Rabbit. The rabbit's 

 circulation is essentially as in our bodies. The heart is 

 completely divided into two parts, the right and left halves. 

 The right half pumps the blood to the lungs, whence it 

 returns to the left half of the heart to be pumped to all the 

 other parts of the body through the main artery, called the 

 aorta. The heart is within a pericardium, situated between 

 the two lungs, and resting against the diaphragm, near the 

 ventral body wall. 



How the Rabbit Breathes. The rabbit's respiration, too, 

 is very like ours. The diaphragm is a thin sheet of muscle 

 that arches across the 

 body at about the pos- 

 terior border of the longer 

 ribs, separating the body 

 cavity completely into two 

 cavities, the anterior con- 

 taining the heart and 

 lungs, the posterior con- 

 taining the stomach and 

 intestines, with the liver, 

 pancreas, kidneys, blad- 

 der, etc. By the shorten- 

 ing of its muscle fibers 

 the diaphragm is moved 

 backward, thus drawing in the air. The muscles which 

 move the ribs in and out also do part of the work. The 

 lungs are similar to ours, being light (hence called 

 "lights") and porous, all the air vesicles being reached 

 by minute branches of the bronchial tubes, which fork 

 from the windpipe. The temperature of the rabbit's 

 blood is considerably higher than our own, averaging 103 

 or 104 F. 



FIG. 150. CROSS SECTION OF ABDOMEN 

 OF MAMMAL. 



