The boys had separate brains, but they shared a major vein in the back of the head called the sagittal superior sinus, a large canal through which blood flows toward the heart.
But doctors still could not be sure that the girls did not share a single sagittal sinus (a major vein returning blood from the top of the brain toward the heart).
Rodney, who got the sagittal vein which the twins had formerly shared, drifted in out of sleep.