appeared to have dissected the eye and related the brain to vision. He also suggested that the brain, not the heart, was the organ that ruled the body (what Stoics would call the hegemonikon) and that the senses were dependent on the brain. According to ancient authorities, Alcmaeon believed the power of the brain to synthesize sensations made it also the seat of memories and thought. The author of On the Sacred Disease, part of the Hippocratic corpus, likewise believed the brain to be the seat of intelligence. The debate regarding the hegemonikon persisted among ancient Greek philosophers and physicians for a very long time. Already in the 4th century BC, Aristotle thought that the heart was the seat of intelligence, while the brain was a cooling mechanism for the blood. He reasoned that humans are more rational than the beasts because, among other reasons, they have a larger brain to cool their hot-bloodedness. On the opposite end, during the Hellenistic period, Herophilus and Erasistratus of Alexandria engaged in studies that involved dissecting human bodies, providing evidence for the primacy of the brain. They affirmed the distinction between the cerebrum and the cerebellum, and identifying the ventricles and the dura mater. Their works are now mostly lost, and we know about their achievements due mostly to secondary sources. Some of their discoveries had to be re-discovered a millennium after their death. During the Roman Empire, the Greek physician and philosopher Galen dissected the brains of oxen, Barbary apes, swine, and other non-human mammals. He concluded that, as the cerebellum was denser than the brain, it must control the muscles, while as the cerebrum was soft, it must be where the senses were processed. Galen further theorized that the brain functioned by the movement of animal spirits through the ventricles. He also noted that specific spinal nerves controlled specific muscles, and had the idea of the reciprocal action of muscles. Only in the 19th century, in the work of François Magendie and Charles Bell, would the understanding of spinal function surpass that of Galen. Medieval to early modern Islamic medicine in the middle ages was focused on how the mind and body interacted and emphasized a need to understand mental health. Circa 1000, Al-Zahrawi, living in Islamic Iberia, evaluated neurological patients and performed surgical treatments of head injuries, skull fractures, spinal injuries, hydrocephalus, subdural effusions and headache. In Persia, Avicenna (Ibn-Sina)