MORPHOLOGY OF ANIMALS 



itself (Fig. 17, A and A^j. In air-breathing amphibia a 

 part of the blood passes directly from the heart to the 

 lungs, whence it returns to the heart oxygenated, while 

 a part of it goes at once to the body (Fig. 16, Bj ; the 

 former is known as the pulmonary, the latter as the sys- 

 temic circulation. In these animals the heart is incom- 

 pletely divided by a partition which separates the 

 auricular chamber into two auricles, but which leaves the 

 ventricle undivided (Fig. 17, B). The blood returning 

 from the body is carried into the right auricle, while that 

 from the lungs goes into the left; in the ventricle both 

 kinds of blood mingle to a certain extent, though by a 

 peculiar arrangement of folds and valves the larger part 

 of the oxygenated blood which enters the left auricle is 

 pumped to the anterior part of the body, while the blood 

 from the right auricle goes to the lungs and to the posterior 

 part of the body. Finally in all birds and mammals and in 



A 



B 







Fig. 17. Diagrams of Hearts of different classes of Vertebrates. A, Heart of Fish viewed 

 from left side ; i auricle and l ventricle ; arrow shows course of blood through the heart, 

 entering the thin-walled auricle (a), passing through the thick-walled ventricle {v) and 

 issuing from the heart through the conus arteriosus {c) into the ventral aorta; the valves arc 

 flaps protruding into the ventricle and conus. Ai, same viewed from ventral side, B, Heart of 

 Amphibians, 2 auricles and l ventricle. C, Heart of Birds and Mammals, 2 auricles and 2 

 ventricles; course of blood shown by arrows. (After Hatschek). 



n5i : 



