at the portal and hepatic veins form one continuous system, which
taken in the totality, represents the companion veins of the arteries of
the abdominal viscera. The liver under this interpretation appears as a
gland developed midway upon these veins, and dismembering them into a
mesh of countless capillary vessels, (a condition necessary for all
processes of secretion,) for the special purpose of decarbonizing the
blood. In this great function the liver is an organ correlative or
compensative to the lungs, whose office is similar. The secretion of the
liver (bile) is fluidform; that of the lungs is aeriform. The bile being
necessary to the digestive process, the liver has a duct to convey that
product of its secretion to the intestines. The trachea is as it were
the duct of the lungs. In the liver, then, the portal and hepatic veins
being continuous as veins, the two systems, notwithstanding their
apparent distinctness, caused by the intervention of the hepatic
lobules, may be regarded as the veins corresponding with the arteries of
the coeliac axis, and the two mesenteric. The hepatic artery and the
hepatic veins evidently do not pair in the sense of afferent and
efferent, with respect to the liver, both these vessels having
destinations as different as those of the bronchial artery and the
pulmonary veins in the lungs. The bronchial artery is attended by its
vein proper, while the vein which corresponds to the hepatic artery
joins either the hepatic or portal veins traversing the liver, and in
this position escapes notice.[Footnote]

[Footnote: In instancing these facts, as serving under comparison to
explain how the hepatic vessels constitute no radical exception to the
law of symmetry which presides over the development and distribution of
the vascular system as a whole, I am led to inquire in what respect (if
in any) the liver as an organ forms an exception to this general law
either in shape, in function, or in relative position. While seeing that
every central organ is single and symmetrical by the union of two
absolutely similar sides, and that each lateral pair of organs is double
by the disunion of sides so similar to each other in all respects that
the description of either side serves for the other opposite, it has
long since seemed to me a reasonable inference that, since the liver on
the right has no counterpart as a liver on the left, and that, since the
spleen on the left has no counterpart as a spleen o