(77) Timaeus: of the skin and flesh they cut for hidden channels two veins along the back, seeing that the body was in fact double, with right side and left; and these they drew down along by the spine, keeping between them the spermatic marrow, in order that this might thrive as much as possible, and that the stream of moisture from there, being in a downward course, might flow easily to the other parts and cause the irrigation to be uniform. After this