ON GENEEATION. 419
But as soon as the sternum is fashioned the heart enters into the chest as into a dwelling which it had built and arranged for itself; and there, like the tutelary genius, it enters on the government of the surrounding mansion, which it inhabits with its ministering servants the lungs. The liver and stomach are by and by included within the hypochondria, and the intestines are finally surrounded by the abdominal parietes. And this is the reason wherefore without dissection the heart can no longer be seen pulsating in the hen's egg after the tenth day of incu- bation.
About this epoch the point of the beak and the nails appear of a fine white colour ; a quantity of chylous matter presents itself in the stomach ; a little excrement is also observed in the in- testine, and the liver being now begun, some greenish bile is perceived ; facts from which it clearly appears that there is another digestion and preparation of nutriment going on be- sides that which takes place by the branches of the umbilical veins ; and it is reasonable matter of doubt how the bile, the excrementitious matter of the second digestion, can be separated by the instrumentality of the liver from the other humours, when we see it produced at the same time as this organ.
In the order now indicated are the internal organs generated universally ; in all the animals which I have dissected, particu- larly the more perfect ones, and man himself, I have found them produced in the same manner : in these, in the course of the second, third, and fourth month, the heart, liver, lungs, kidneys, spleen, and intestines present themselves inchoate and increasing, and all alike of the same white colour which belongs to the body at large. Wherefore these early days are not im- properly spoken of as the days when the embryo is in the milk ; for with the exception of the veins, particularly those of the umbilicus, everything is as it were spermatic in appearance.
I am of opinion that the umbilical arteries arise after the veins of the same name, because the arteries are scarcely to be discovered in the course of the first month, and take their rise from the branches that descend to either lower extremity. I do not believe, therefore, that they exist until that part of the body whence they proceed is formed. The umbilical veins, on the contrary, are conspicuous long before any part of the body is begun.
