Page:The Works of William Harvey (part 1 of 2).djvu/516

 subsequently along with the other viscera, so must they be re- ferred to the same class of parts as these, namely, the third.

In the production of the circulating system the veins are sooner seen than the arteries ; such at least is our conclusion.

The second process, which begins after the fourth day, is indi- cated by a certain concrescence, which I designate vermiculum worm or maggot ; for it has the life and obscure motions of a maggot; and as it concretes into a mucous matter, it divides into two parts, the larger and superior of which is seen to be conglobed, and divided, as it were, into thin vesicles, the brain, the cerebellum, and the two eyes ; the less, again, con- stituting the carina, arises over the vena cava and extends in the line of its direction.

In the genesis of the head, the eyes are first perceived ; by and by a white point makes its appearance in the situation of the beak, and the slime drying around it, it becomes invested with a membrane.

The outline of the rest of the body follows about the same period. First, from the carina something like the sides of a ship are seen to arise ; the parts having an uniform consistence in the beginning, but the ribs being afterwards prefigured by means of extremely fine white lines. The instruments of loco- motion next arise the legs and wings ; and the carina and the extremities adnate to it are then distinguished into muscles, bones, and articulations.

These two rudiments of the head and trunk appear simul- taneously, but as they grow and advance to perfection subse- quently, the trunk increases and acquires its shape much more speedily than the head ; so that this, which in the first instance exceeded the whole trunk in size, is now relatively much smaller. And the same thing occurs in regard to the human embryo.

The same disparity also takes place between the trunk and the extremities. In the human embryo, from the time when it is not longer than the nail of the little finger, till it is of the size of a frog or mouse, the arms are so short that the extre- mities of the fingers could not extend across the breast, and the legs are so short that were they reflected on the abdomen they would not reach the umbilicus.

The proportion of the body to the extremities in children after their birth continues excessive until they begin to stand