This member has three ventricles or chambers, like the brain. One ventricle is on the right side, the second on the left, and the third in between. The right ventricle towards the liver has two orifices. One is towards the liver and is very large. Into this there enters a vein called _vena chilis_, which arises in the convexity of the liver and brings the blood from the liver to the heart. In that right ventricle the blood is purified, and then sent by the heart to all the other members. Now since the heart attracts by this orifice of the _vena chilis_ more than it expels, therefore nature ordains that in the moment of contraction when the blood is expelled this orifice closes, and when the heart dilates it opens. Moreover there are three little valves (_hostiolitti_) or doors opening from without inward, and these valves are not very depressed; so that by this same orifice only part of the purified blood is expelled to the other members, because part goes to the lungs and the remainder forms the vital spirit; therefore nature ordains that these valves do not entirely close. From the _vena chilis_, before it enters the cavity of the heart, there arises another vein, which surrounds the root of the heart; and from it are given off branches which disperse themselves through the substance of the heart, and from the blood of that vein the heart nourishes itself. The right ventricle towards the lung has another orifice into which opens the _arterial vein_, bringing the blood from the heart to nourish the lung: in this orifice also are three valves (_hostioli_) opening from within outward and closing from without inward, in the opposite way to the valves of the other orifice; and this is so that they should entirely close. Hence by this orifice the heart during the period of contraction can expel, and yet during the period of its dilatation cannot attract anything through it as was done in the first orifice. The left ventricle of the heart has its sides denser and thicker than the sides or walls of the right ventricle; and this for three reasons: Firstly, because in the right ventricle is contained the blood, which is heavy, while in the left ventricle there is spirit, which is very light; therefore in order that the heart should not be heavier and more ponderous on one side than on the other, it was necessary to compensate in this manner, that is, that the left ventricle should be thicker in its walls than the right. In the second place, the spirit being more subtil and more volatile (_resolubile_) than blood, it needs a stronger habitation and better supports. Thirdly, the left ventricle is much warmer than the right, because in it is generated the spirit from the blood, by a great heat which makes that blood more subtil; and heat is better preserved in a substance that is dense and thick.