20 



Vertebrate. 



FIG. 10. 



sometimes prolonged at its outlet into a conical part 



full of valves, called the 

 arterial cone, which ends 

 in the large main blood- 

 vessel, or aorta. The 

 arterial cone is well de- 

 veloped in sharks. 



Sometimes, as in 

 most of our common 

 fishes, the aorta at its 



A, the aortic bulb ; H, heart ; B, 

 branchial arches ; b, branchial 

 veins retaining the blood to A, 

 the aorta ; v, v, the veais. 



B shows the structure of one of the 

 branchial arches, with its ap- 

 pended gill filaments, bc> The 

 blood from the aortic bulb 

 passes through B, the branch- 

 ial artery, is aerated in the fila- 

 ments &:, collected and returned 

 by b, the branchial vein, into A, 

 the dorsal aorta. 



Diagram of the circulation in a fish. 



