Timaeus

And when all the limbs and parts of the mortal living creature had been naturally joined together, it was so that of necessity its life consisted in fire and air; and because of this it wasted away when dissolved by these elements or left empty thereby; wherefore the Gods contrived succour for the creature. Blending it with other shapes and senses they engendered a substance akin to that of man, so as to form another living creature: such are the cultivated trees and plants and seeds which have been trained by husbandry and are now domesticated amongst us; but formerly the wild kinds only existed, these being older than the cultivated kinds. For everything, in fact, which partakes of life may justly and with perfect truth be termed a living creature. Certainly that creature which we are now describing partakes of the third kind of soul, which is seated, as we affirm, between the midriff and the navel, and which shares not at all in opinion and reasoning and mind but in sensation, pleasant and painful, together with desires. For inasmuch as it continues wholly passive and does not turn within itself around itself, repelling motion from without and using its own native motion, it is not endowed by its original constitution with a natural capacity for discerning or reflecting upon any of its own experiences. Wherefore it lives indeed and is not other than a living creature, but it remains stationary and rooted down owing to its being deprived of the power of self-movement. And when our Superiors had generated all these kinds as nutriment for us inferior beings, they channelled out our body itself, like as if they were cutting channels in gardens, to the end that it might be irrigated as it were by an inflowing stream. And firstly, beneath the junction 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 they clave the veins round the head and interlaced them, and drew them opposite ways, bending those from the right of the head to the left and those from the left to the right, in order that they, together with the skin, might serve as a bond between the head and the body, seeing that the head was not encircled by sinews at the crown; and in order, also, that the sense-impressions derived from the parts on either side might be manifest to the whole body.