Page:The Works of William Harvey (part 1 of 2).djvu/493

 appears that the veins do by no means all proceed from the liver as their origin and commencement, but from the heart unless indeed any one would be hardy enough to contend that a vessel proceeded from its branches, not the branches from the trunk of the vessel.

Moreover, as the vessels in question are distributed equally to the albumen and vitellus of the egg, not otherwise than as the roots of trees are connected with the ground, it is obvious that both of these substances must serve for the nutriment of the embryo, and that they are taken up and carried to it by these vessels. But this view is opposed to that of Aristotle, who everywhere maintains that the chick is formed from the albumen, and receives nourishment through the umbilicus alone. The albumen indeed is first consumed, and the yelk serves subse- quently for food, supplying the place of the milk, which viviparous animals receive after their birth from their mothers. The food which nature provides for the young of viviparous tribes in the dug of the mother, she supplies in the yelk of the egg to the young of oviparous animals. Whence it happens, that when the albumen is almost wholly consumed, the vitellus still re- mains nearly entire in the egg, the chick being already perfect and complete; more than this, the yelk is still found in the abdomen of the chick long after its exclusion. Aristotle dis- covered some on the eighteenth day after the hatching; and I have myself seen a small quantity connected with the intestine at the end of six weeks from that epoch.

Nevertheless, from the yelk (which certainly does not de- crease in the same ratio as the albumen whilst the chick is forming) that is taken into the abdomen of the chick, and from the distribution of vessels through its substance, the whole of these collecting into a single trunk which enters the porta of the liver, and doubtless carrying that portion of yelk they have absorbed for more perfect elaboration in that viscus these and other arguments of the like kind force me to say that I cannot do otherwise than admit with Aristotle that the yelk supplies food to the chick, and is analogous to milk.

The whole of the yelk, indeed, does not remain after the foetus of the fowl is fully formed ; for a certain portion of it has been liquefied on the very first appearance of the embryo, and receives branches of vessels no less than the albumen, by which,