s and veins may be compared to a tree, whose trunk is
divided into large branches; these are subdivided into smaller, the
smaller again into others still smaller; and we may observe,
likewise, that the sum of the capacities of the branches, which arise
from any trunk, is always greater than the capacity of the trunk.

The minutest branches of the arteries, being reflected, become veins,
or else they enter veins that are already formed, by anastomosis, as
it is called; the small veins continually receiving others, become,
like a river, gradually larger, till they form the venae cavae, which
conduct the blood to the heart.

Anatomical injections prove, that the last branches of the arteries
terminate in the beginning of veins; but it is the opinion of many
celebrated physiologists, that the arteries carry the blood to the
different parts of the body to nourish them, and that the veins
commence by open mouths, which absorb or suck up what is superfluous,
and return it back to the heart.

From what has been said, it must be evident that there is a
considerable resemblance between the circulation of the blood in the
animal body, and the circulation of the aqueous fluid on the surface
of the globe. In the latter case the water is raised from the ocean,
by the heat of the sun, and poured down upon the dry land, in minute
drops, for the nourishment and economy of its different parts. What
is superfluous is collected into little rills; these meeting with
others, form brooks; the union of which produce rivers, that conduct
the water to its original source, from which it is again circulated.

In the same manner, the blood is sent by the heart to different parts
of the body, for the nourishment and economy of its different parts;
what is superfluous is brought back by veins, which, continually
uniting, form those large trunks, which convey the vital fluid to the
heart.

The blood does not circulate, however, in the manner which I have
mentioned, in all parts of the body; for that which is carried by
arteries to the viscera, serving for digestion, such as the stomach,
bowels, mesentery, omentum, and spleen, is collected by small veins
which unite into a large trunk called the vena portarum; this vein
enters the liver, and is subdivided in it like an artery,
distributing through the liver a great quantity of blood, from which
the bile is secreted: and, having served this purpose, the blood is
collected by small veins; these uni