Herophilus made many anatomical discoveries. He traced the delicate arachnoid membrane into the ventricles of the brain, which he held to be the seat of the soul; and first described that junction of the six cerebral sinuses opposite the occipital protuberance, which to this day is called the _torcular Herophili_. He saw the lacteals, but knew not their use, and regarded the nerves as organs of sensation arising from the brain; he described the different tunics of the eye, giving them names which are still retained; and first named the duodenum and discovered the epididymis. He attributed the pulsation of arteries to the action of the heart; the paralysis of muscles to an affection of the nerves; and first named the furrow in the fourth cerebral ventricle, calling it _calamus scriptorius_. Erasistratus gave names to the auricles of the heart; declared that the veins were blood-vessels; and the arteries, from being found empty after death, were air-vessels. He believed that the purpose of respiration was to fill the arteries with air; the air distended the arteries, made them beat, and in this manner the pulse was produced. When once the air gained entrance to the left ventricle, it became the vital spirits. The function of the veins was to carry blood to the extremities. He is said to have had a vague idea of the division of nerves into nerves of sensation and of motion; to the former he assigned an origin in the membranes of the brain, while the latter proceeded from the cerebral substance itself. He recognized the use of the trachea as the tube which conveys air to the lungs. A catheter, the first invented, which was figured in ancient surgical works, bore the name of the catheter of Erasistratus. He gravely tells us, as the result of his anatomical studies, that the soul is located in the membranes of the brain. The practice of human dissection did not long exist in the city of its origin, and after the second century was unknown. Then science underwent a retrogression; observations and experiments were replaced by useless discussions and subtle theories. The decline of the Alexandrian University was due to a series of disasters which began with the Roman domination and reached their climax with the capture of the city by the Arabs. [Illustration: GALEN]