2. In all other animals which have a chest the heart is placed in the centre; in man it is rather on the left side, inclining a little from the division of the mammæ towards the left breast in the upper part of the chest; it is not large; its whole form is not long, but rather round, except that the extremity ends in a point. It has three cavities, as I have said. The greatest is that on the right, the least on the left, the middle one is of intermediate size. They are all perforated towards the lungs. It has both the two smaller, and all of them perforated towards the lungs, and this is evident in one of the cavities downwards from its point of attachment. 3. Near the principal cavity it is attached to the great vein to which also the mesenterium is united, and in the middle it is attached to the aorta. Passages lead from the lungs to the heart, and they are divided in the same way as the trachea, following the passages from the trachea throughout the whole lungs, and the passages leading from the heart are on the upper part. There is no passage which is common to them both, but by their union they receive the breath and transmit it through the heart; for one of the passages leads to the right cavity, and the other to the left. We will hereafter speak of the great vein and the aorta in the portion of our work which treats of these parts. 4. In all animals which have lungs and are viviparous, either internally or externally, the lung has more blood than all the other parts; for the whole lung is spongy, and through each perforation branches of the great vein proceed. Those persons are deceived who say that the lungs are empty, drawing their conclusion from dissected animals, from which all the blood has escaped. Of all the viscera the heart alone contains blood, and in the lungs the blood is not in the lungs themselves, but in the veins by which they are perforated. But in the heart itself the blood is in each of the cavities, but the thinnest blood is in the middle cavity. 5. Beneath the lungs is that division of the trunk which is called the diaphragm. It is united to the ribs, the hypochondriac region, and the spine. In the centre is a smooth membranous part, and there are veins extending through it. The human veins are thick in proportion to the size of the body. Under the diaphragm, on the right side is the liver, on the left the spleen, alike in all animals which are furnished with these parts in their natural form and without monstrosity, for already there has been observed an altered order in some quadrupeds. They are joined to the abdomen near the omentum.