The Hippocratic authors confounded the arteries with the veins. Praxagoras first distinguished two kinds of vessels which he supposed to contain air, whence the name artery. Aristotle and Erasistratus maintained this view, which prevailed until the time of Galen, who devoted a book to the refutation of it, basing his argument upon the observation that always when an artery is wounded blood gushes out. How near he came to being the discoverer of the circulation may thus be seen. A little less reverence for authority and a little more capacity for observation would have placed him in possession of the knowledge, lack of which for so many centuries retarded the whole profession. He thought the veins originated from the liver--in this respect being behind Aristotle--but considered the heart as the common source of the arteries and veins. Even the portal system of veins confused him, and he erroneously described a superior and inferior aorta, but atoned for this by describing the umbilical veins and arteries. Aristotle also had supposed all the nerves originated from the heart, but Galen stated that they are derived from the brain and spinal marrow, and pointed out two kinds of nerves: those of sensation, which he thought proceeded from the brain, and those of motion, which he considered{041} to originate in the spinal marrow. Thus, he described distinct nerves of sensation and motion, but sadly confused their anatomy. He seems also to have had some notion of the great sympathetic, although it was by no means accurate. He suggested the division of the principal nerves, in order to prove the fact that nervous energy is transmitted from the encephalon to other parts of the body. He speaks of glands, and thought they discharged their secretions through veins into the various cavities, but regarded them rather as receptacles of excrementitious matter than as agents for secretion of valuable fluids. He even regarded the mammæ as glandular bodies in this sense, although he knew, of course, the value of their secretion. To Galen we owe the division of the body into cranial, thoracic, and abdominal cavities, whose proper viscera and envelopes he described. He spoke of the heart as having the appearance of a muscle, but differing from it. He regarded it as the source of natural heat, and the seat of anger and of violent passions. He appreciated that inspiration is carried on by enlargement of the thoracic cavity. He thought that atmospheric air entered the cavity of the cranium through the cribriform plate of the ethmoid and passed out by the same route, carrying with it excrementitious humors from the brain, which were discharged into the nasal fossæ. But some portion of air thus entering remained, according to his views, and combined with the vital spirits in the anterior ventricles of the brain, from which combination originated the animal spirits and immediate agents of the rational soul. These