20 CIRCULATION.— RESPIRATION. 



36. The large intestine is very short, and terminates by a 

 dilatation called cloaca, which receives the urine as well as the 



eggs- 



37. The ch5^1e; derived from the digestion of food, is absorbed 

 by the chyliferous vessels, which unite with the lymphatic vessels 

 of the extremities to form two thoracic ducts, which mount in 

 front of the vertebral column, and empty into the jugular veins, 

 near the heart. 



38. The blood of birds does not contain circular globules like 

 that of mammals, but oval globules like those contained in the 

 blood of reptiles and fishes. These solid particles are more 

 abundant in birds than in other vertebrate animals, and the tem- 

 perature of this liquid is higher than in the mammalia, which are 

 nevertheless, warm blooded animals, 



■-■39. The circulation is carried on in the same manner as in 

 the mammalia ; it is double and complete, that is, before reach- 

 ing the point from which it departed, the blood passes through 

 two systems of capillary vessels, and all the venous blood is 

 changed into arterial blood. 



40. The heart has four cavities, namely : one ventricle and 

 one auricle placed on the left, and the same on the right side. 

 The blood is forced by the left ventricle into the aorta, which dis- 

 tributes it to the capillary vessels of all parts of the body. This 

 liquid then returns to the heart through the veins, and enters the 

 right auricle, which forces it into the right ventricle which is 

 situate beneath it; this last cavity, by contracting, sends the 

 blood to the lungs, through the pulmonary artery ; from the 

 pulmonary artery the blood passes into the capillary vessels of 

 the lungs, where it is changed into arterial blood ; then it enters 

 the pulmonary veins, and passing through them, reaches the left 

 auricle ; finally, the left auricle pours it into the left ventricle, 

 whence we have just seen it go forth to be distributed to all the 

 organs. 



41. Birds are distinguished from all other vertebrate animals 

 by their mode of respiration, which is aerial, as it is in the mam- 

 malia and reptiles ; and it takes place not only in the lungs, but 

 also in the substance of all the other organs. In the mammalia 



36. What is the cloaca? 



37. What becomes of the chyle formed by the process of digestion ? 



38. What is remarkable about the globules in 'the blood of birds? 



39. What is the character of the circulation in birds? 



40. What route is taken by the blood in completing its circuit through the 

 body? 



41. What are the peculiarities of respiration in birds? In what respect 

 do the lungs of birds differ from the same organs in mammals ? 



