Whether the heart is pyramidal in shape.
Why its apex [conus] does not rise upward in quadrupeds, as it does in fish.
Why it is not located in the middle of the human [ body] .
Why it affords very poor nourishment although it is the best member.
Next one asks whether the heart is pyramidal in shape. It seems not, because a more perfect organ deserves a more perfect shape, and the heart, since it is a more perfect member, will have a more perfect shape. But this is a spherical or round shape, and therefore, etc.
Second, one asks why its apex [conus] does not rise upward in quadrupeds, as it does in fish, whereas in quadrupeds its base rises upward.
Third, one asks why it is not located in the middle of the human [body] as it is in other animals, since the human should be most suitably proportioned.
Fourth, one asks why it affords very poor nourishment although it is the best and a noble member.
To the first, one must reply that among all the members the heart is hottest. But in a foreign matter heat tends to form a pyramidal shape, as is clear from fire in wood, which is in a foreign matter, and this is why the heart has a pyramidal shape, and also so that it might infuse life better to the rest of the body.
To the second, one must reply that the heart is opposite the brain so that the one may be tempered by the other. But in quadrupeds the heart is warmer than in fish, and this is why, if the base of the heart were below and the apex were above, the heart would overheat the lower members and would not be adequately tempered by the brain. Therefore, the heart's aperture is in the part facing the brain in quadrupeds, in order to be tempered better by the brain's coldness and, conversely, in order better to temper the brain. But there is not as much heat in fish. Therefore, if the heart's aperture faced the brain, the heat would be very quickly extinguished by the brain's coldness and the coldness of the water that enters into it.
To the third, one must reply that the maximum balance is required in the human, and this is why the heart is located on the left, because it infuses power toward its right side, so that what is on the right will acquire by its influence what the left side acquires by its location. And in addition to this the spleen, which is receptive of melancholy, is on the left side, and this is why the left side is not overly cooled by the spleen, nor the right side overly heated by the liver and the gall bladder, because the heart tends downward toward the left side from the liver on the right, etc.
To the fourth, one must reply that the heart is a member that endures a long time and has a nature that retains its disposition, and this is why it is naturally solid and very compact. Things of this sort afford poor nourishment because they resist digestion and they fatigue the power of digesting, and this is why, etc.
Whether the upper intestines should be thinner and longer and more delicate than the lower ones.
One asks whether the upper intestines should be thinner and longer and more delicate than the lower ones.
It seems not. For undigested food occupies a larger volume than digested food. Therefore, the upper intestines ought to be broader and thicker than the lower ones.
One must reply that in the human the powers are regulated by reason. Thus his imaginative power not only extends to the nutritive power but concerns other things as well. And this is the reason that, in order for the food to remain for a longer period of time in the human, nature has ordained that the upper intestines be long and thin. They are long so that the pure food will not be absorbed by them all at once but so that to the contrary, what is not absorbed in one part will be absorbed in another. Otherwise, the human would have to eat continuously as brute beasts do. But feces from the food are thick and earthy, and this is why they demand thicker and wider vessels, and this is why the upper and lower intestines differ with respect to being thin and thick, broad and long and short, as it evident in the study of anatomy.
-  Conus: In the DA, A. uses acumen for this pointed feature of the heart; see, e.g., 126.96.36.1993 (SZ 1: 268).