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the inside of each gill. Each efferent branchial vein is a 

 blood vessel having a definite wall. 



There are nine efferent branchial veins (ef. 1-9) 

 corresponding to the nine afferent branchial sinuses one 

 for each gill. 



The Branchio-cardiac veins (fig. 54) convey the pure 

 blood from the efferent branchial veins to the peri- 

 cardium. There are five branchio-cardiac veins at each 

 side. They have definite walls. 



First Branchio-cardiac vein (be. 1) receives the first 

 and second efferent branchial veins. It passes up the 

 outer side of the pleural muscle chamber of the second 

 thoracic segment, above the first pleural sinus. 



Second Branchio-cardiac vein (be. 2) receives the third, 

 fourth and fifth efferent branchial veins. It passes up the 

 outer side of the third thoracic pleural muscle chamber. 

 The first and second branchio-cardiac veins enter the 

 pericardium together through the first opening (see section 

 on Pericardium). 



Third Branchio-cardiac vein (be. 3) receives the sixth 

 and seventh efferent branchial veins. It passes up the 

 fourth thoracic pleural muscle chamber. It enters the 

 pericardium by means of the second pericardia! opening. 



Fourth Branchio-cardiac vein (be. 4) receives the 

 eighth efferent branchial vein, and passes up the fifth 

 pleural muscle chamber. 



Fifth Branchio-cardiac vein (be. 5) receives the ninth 

 efferent branchial vein and passes up the sixth pleural 

 muscle chamber. The fourth and fifth branchio-cardiac 

 veins enter the pericardium through the third pericardial 

 opening. 



There are no valves between the branchio-cardiac 

 veins and the pericardium 



