Drains blood from myocardium into right atrium

Coronary Sinus

Explanation:

A coronary sinus is a group of small veins that collectively from the sinus which is nothing but a large sized vessel. This sinus is located along the rear side of heart between the left ventricle and left atrium.  

This sinus collects cardiac venous blood which comes from the mycocardium and the thick muscle layer with in the heart and facilitates its movement to the right atrium.

answer; i believe that the correct answer is ; males are hemizygous for the x chromosome;

for a different answer set the answer would be because the oxygen in the water had depleted (apex)