568 THE UMBILICAL CORD.
minute, that they are woven, as it were, like the most delicate threads, into the tissues of the veins, or rather in some obscure manner insinuate themselves into them ; hence they almost entirely elude the sight. But all the veins, by a retrograde movement, unite their twigs and terminate in one trunk like the branches of a tree, in the same manner as the mesenteric veins, all of which terminate in the vena portse.
Near the embryo [the umbilical veins] are divided into two trunks, but when entered within it they constitute one um- bilical vein, which ends in the vena cava, near the right auricle of the heart, and passes through the liver, entering the vena portse ; giving off no branches besides until it leaves the con- vex portion of the liver by a very large orifice. So that if the vena cava is opened from the right auricle downwards and emptied of blood, three apertures may be seen close to each other; one is the entrance of the vena cava descendens, the second that of the hepatic vein, which ramifies throughout the convex portion of the liver, and the third is the origin of the umbilical vein. Hence it is quite clear that the origin of the veins is by no means to be looked for in the liver ; inasmuch as the orifice of the vena cava descendens is much larger than the hepatic branch, which is indeed equalled in size by the um- bilical vein. For the branches are not said to be the origin of their trunk ; but where the trunk is greatest there the origin of the veins is to be looked for, and this is the case at the entrance of the right ventricle : here, then, the origin of all veins, and the storehouse of the blood must be placed.
To return to the umbilical vessels, which are not subdivided in the same way in all animals; for in some two or more branches of veins are found within the body of the foetus, some of which pass through the liver, whilst others join the portal and mesenteric veins. In the human foetus, at a dis- tance of three or four fingers' breadth from the umbilicus, the trunks of the arteries and veins are involved together in a complicated manner, (as if one were to twist several waxen tapers in the form of a stick,) and are besides covered and held together by a thick gelatinous membrane. This cord passes on towards the chorion, and w T hen arrived at the concave por- tion of the placenta and the inner surface of the chorion, splits into innumerable branches; these divide again, and constitute
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