Claudius Galenus, the celebrated Roman physician whose writings were for centuries accepted as authority and whose reputation was second only to that of Hippocrates, was obliged to base his anatomical treatises largely upon the dissection of the lower animals. He advised his pupils to visit Alexandria, where he had studied, in order that they might examine the human skeleton. He complained that the physicians of his time—in the reign of Marcus Aurelius—had entirely neglected anatomical knowledge and had degenerated into mere sophists. He appreciated the importance of anatomy, particularly to a surgeon who is called upon to treat wounds and injuries. Hence he has endeavored in the four books, _De Anatomicis Administrationibus_, to cover this part of anatomy as exhaustively as possible. Galen’s voluminous writings form a precious monument of ancient medicine. The works of the Alexandrian anatomists having been destroyed, we know of their labors chiefly from what Galen has said of them. His treatises show a remarkable familiarity with practical anatomy, although his dissections were made upon the lower animals. Galen’s knowledge of osteology was extensive. He described the bones of the skull, the cranial sutures, and the essential features of the malar, maxillary, ethmoid and sphenoid bones. He divided the vertebrae into cervical, dorsal and lumbar classes. He knew that both arteries and veins were blood-carrying vessels; he described the valves of the heart, and recognized this organ as the source of pulsation. He erroneously taught that the interventricular septum presents foramina through which the two kinds of blood become mixed.