Next comes the middle region, or chest, containing the vital faculties and organs. As I have said, it is separated from the lower abdomen by the diaphragm, or midriff, a sheet consisting of many nerves and membranes, which, among its other functions, is the instrument of laughter. A thin, sinewy membrane called the pleura also lines the whole chest; when inflamed, it is the seat of the disease called pleurisy. Some add a third membrane, called the mediastinum, dividing the chest into right and left parts.

The principal organ of this region is the heart, the seat and fountain of life, heat, spirits, pulse and breathing; the sun of our body, its king and sole commander, the seat and organ of all passions and feelings. In every creature it is the first to live and the last to die. Pyramidal in shape, rather like a pine cone, it deserves admiration for producing such a variety of feelings. Through their movements it expands or contracts, stirring and directing the body’s humours: black bile in sorrow, yellow bile in anger, sending blood outward in joy and drawing it inward in sorrow, moving the humours as horses move a chariot.

Although the heart is a single organ, it can be divided into two chambers, right and left. The right resembles a waxing moon and is larger than the other. It receives blood from the vena cava, sending some to the lungs to nourish them and the rest to the left side to generate spirits. The left chamber is cone-shaped and is the seat of life. It draws blood to itself as a torch draws oil, producing spirits and fire from it. Spirits are in the blood as fire is in a torch. Through the great artery called the aorta, the heart sends vital spirits throughout the body, and through the artery called the venosa it draws air from the lungs. Both chambers therefore have their vessels: the right has two veins, the left two arteries, besides the two folded, ear-like appendages that serve them both, one to hold blood and the other air for their different uses.

The lungs are a thin, spongy organ shaped like an ox’s hoof, according to Fernel. One writer calls them the town clerk or crier. They are the instrument of voice, joined to the heart like an orator to a king, giving voice to its thoughts. That they are the instrument of voice is evident, since no creature lacking lungs can speak or utter any sound. They are also the instrument of respiration, or breathing, and their function is to cool the heart by sending air to it through the venosal artery. This vein reaches the lungs by way of the windpipe, which consists of many pieces of cartilage, membranes and nerves; it takes in air through the nose and mouth and likewise breathes out the heart’s fumes.

In the upper region, which serves the faculties of sensation and movement, the chief organ is the brain: a soft, white, marrow-like substance generated from the purest part of the seed and spirits, enclosed by several coverings and seated within the skull. It is the noblest organ under heaven, the dwelling and seat of the soul, the home of wisdom, memory, judgement and reason, and the part in which man most resembles God. Nature has therefore covered it with a hard bony skull and two membranes: the dura mater, or meninx, and the pia mater. The dura mater lies next to the skull, above the other membrane, enclosing and protecting the brain. When it is removed, the pia mater appears: a thin membrane immediately covering the brain and also entering into it.

The brain itself is divided into front and rear parts. The front is much larger than the other, which is accordingly called the little brain. The front part has various cavities arranged into ventricles, receptacles for the spirits brought here from the heart through the arteries. Here the spirits are refined into a more heavenly substance to perform the soul’s actions. There are three of these ventricles: right, left and middle. The right and left are named from their positions and generate animal spirits. If they are injured, sensation and movement cease. These ventricles are also held to be the seat of the common sense.

The middle ventricle is a shared cavity where the other two meet. It has two passages: one receives phlegm, while the other extends to the fourth chamber. Here they place imagination and thought. Such are the uses of the three ventricles in the front part of the brain. The fourth chamber, at the back of the head, belongs jointly to the cerebellum, or little brain, and the spinal cord. It is the last and most solid of them all, receiving animal spirits from the other ventricles and conveying them to the spinal cord. Here, they say, memory is seated.