Page:The Works of William Harvey (part 1 of 2).djvu/360

 black points. The pupils of the eyes are distinguished ; the eyelids appear, as does also the membrana nictitans in the greater canthus of the eye, a membane which is proper to birds, and which they use for cleansing the eyeball. The convolutions of the brain farther make their appearance ; the cerebellum is included within the skull ; and the tail acquires the charac- teristic shape of the bird's rump.

After the fourteenth day the viscera, which up to this time have been white, gradually begin to assume a flesh or reddish colour. The heart, having now entered the penetralia of the thorax and been covered with the sternum, inhabits the dwelling place which itself had formed. The cerebrum and cerebellum acquire solidity under the dome of the skull ; the stomach and intestines, however, are not yet included within the abdomen, but, connected with the parts within, hang pendulous externally.

Of the two vessels that proceed from the abdomen to the umbilicus, near the anus, one is an artery, as its pulse proclaims, and arises from the arteria magna or aorta, the other is a vein, and extends from the vitellus by the side of the intestines to the vena portse, situated in the concave part of the liver. The other trunk of the umbilical vessels, collecting its branches from the albumen, passes the convexity of the liver, and enters the vena cava near the base of the heart.

As all these things go on becoming clearer from day to day, so the greater portion of the albumen is also gradually consumed; this, however, is nowise the case with the vitellus, which remains almost entire up to this time, and indeed is seen of the same size as it was the first day.

In the course of the following days five umbilical vessels are conspicuous ; one of these is the great vein, arising from the cava above the liver, and distributing its branches to the albumen ; two other veins proceed from the porta, both having the same origin, and run to the two portions of the vitellus, which we have but just described ; and these are accompanied by two arteries arising one on either side from the lumbars.

The chick now occupies a larger space in the egg than all the rest of the matter included in it, and begins to be covered with feathers ; the larger the embryo grows, the smaller is the quantity of albumen that is present. It is also worthy of ob-