Herophilus:

• 3 great vessel systems: arteries, veins, nerves [H: discoverer system]
• Lacteals
• named duodenum
• arteries have no blood, only "air"
• synanastomoses

Erisistratus:

• 2 Pneuma:
• p. zootikon [vital spirit; distributed via arteries, must pass through brain]
• p. psychikon. [animal spirit: in ventricles, distrib to body via nerves]
• cerebrum distinguished from cerebellum
• tri [Right side, 3 cusps]  and bi [Left side, 2 cusps]  cuspid valves   discovered and named.  Guard Entrance.
• Sigmoid or Semilunar valves Guard Exit [Right: blood to lung; Left:   Pneuma to Body]
• seat of soul in brain, in meninges [~ H]
• Experiment to show valves unidirectional, heart as unidirectional   pump.
• [actually the experiment is described in Hippocratic corpus]
• Arterial blood is pathological
• muscular contraction: pneuma passing through nerve fills hollow space of muscle, which expands and makes the ends contract.
• an idea which lasted until the 17th century
• "copious emanation": like 'insensible perspiration' of Sanctorius.
• Liver produces blood, which veins distribute to nourish the body.
• The right side of the heart has only one purpose: to give blood  to the lung.
• 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.