n the limits of their respective sides of the body,
then their capillary anastomosis could only take place along the median
line, and here in such case they might be separated by median section
into two distinct systems. But as each system is itself double in
branching into both sides of the body, the two would be at the same time
equally divided by vertical section. From this it will appear that the
vessels belonging to each heart form a symmetrical system, corresponding
to the sides of the body, and that the capillary anastomosis of these
systemic veins and arteries is divisible into two great fields, one
situated on either side of the median line, and touching at this line.

IV.--The vessels of the right heart do not communicate at their
capillary peripheries, for its veins are systemic, and its arteries are
pulmonary. The vessels of the left heart do not anastomose, for its
veins are pulmonary, and its arteries are systemic. The arteries of the
right and left hearts cannot anastomose, for the former are pulmonary,
and the latter are systemic; and neither can the veins of the right and
left hearts, for a similar reason. Hence, therefore, there can be,
between the vessels of both hearts, but two provinces of
anastomosis--viz., that of the lungs, and that of the system. In the
lungs, the arteries of the right heart and the veins of the left
anastomose. In the body generally (not excepting the lungs), the
arteries of the left heart, and the veins of the right, anastomose; and
thus in the pulmonary and the systemic circulation, each heart plays an
equal part through the medium of its proper vessels. The pulmonary bear
to the systemic vessels the same relation as a lesser circle contained
within a greater; and the vessels of each heart form the half of each
circle, the arteries of the one being opposite the veins of the other.

V.--The two hearts being, by the union of their similar forms, as one
organ in regard to place, act, by an agreement of their corresponding
functions, as one organ in respect to time. The action of the auricles
is synchronous; that of the ventricles is the same; that of the auricles
and ventricles is consentaneous; and that of the whole heart is
rhythmical, or harmonious--the diastole of the auricles occurring in
harmonical time with the systole of the ventricles, and vice versa. By
this correlative action of both hearts, the pulmonary and systemic
circulations take place synchronously; and the phe