PULMONARY CIRCULATION. 



65 



With the appearance of lungs as respiratory organs (Dipnoi, 

 Perennibranchiate Amphibia, larvae of Salamanders and Batra- 

 chians) (fig. 58), the heart obtains a more complicated structure, 



in that the auricle becomes divided 

 into a right and left division, the 

 latter of which receives the arte- 

 rialised blood, returning from the 

 lungs by the pulmonary veins. 

 The septum between the two 

 divisions of the auricle may, how- 

 ever, remain incomplete (Dipnoi, 

 Proteus). The advehent pulmon- 

 ary vessels, the pulmonary arte- 

 ries, always proceed from the 



FIG. 57. Diagram of the circulator y 

 organs of an osseous fish. V, 

 ventricle ; Sa, aortic bulb with the 

 arterial arches which carry the 

 venous blood to the gills ; Ao, 

 dorsal aorta into which open the 

 vessels from the gills or branchial 

 veins Ab. N, kidney ; D, alimen- 

 tary canal ; L/C, portal circulation. 



FIG. 58. Gills (Sr) and pulmonary sacs (P) 

 of a perennibranchiate amphibian. Ap, 

 pulmonary artery proceeding from the 

 posterior of the four aortic arches. The 

 other three lead to the three pairs of gills ; 

 D, alimentary tract ; A, aorta. 



posterior vascular arch, which, as a rule, loses its relation to the 

 branchial respiration. 



On the disappearance of the gills, which is completed during the 

 metamorphosis in the Salamandrina and Batrachia, the pulmonary 



5 



