Pneuma enters the trachea, passes through fine connections of bronchioles, and the pulmonary vein, via anastomoses, to the bicuspid valve, into the left ventricle, and out into the arteries. Purpose of left side of heart is to distribute pneuma. Pneuma in arteries is derived from outside air, and is not innate. Galen later adds that diastole draws the pneuma in. Body is composed of atoms, vivified by atoms of pneuma.
Vital heat is generated by interaction of venous blood and arterial pneuma.