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 phenomena resulting in both reciprocate and balance each other. In the pulmonary circulation, the blood is aerated, decarbonized, and otherwise depurated; whilst in the systemic circulation, it is carbonized and otherwise deteriorated.