the next developments in the human understanding of pulmonary circulation did not come until centuries later. persian polymath avicenna (c. 980 - 1037 ce) wrote a medical encyclopedia entitled "the canon of medicine". in this book, he translated and compiled contemporary medical knowledge and added some new information of his own. however, avicenna's description of pulmonary circulation reflected the incorrect views of galen. the arab physician, ibn al-nafis, wrote the "commentary on anatomy in" "avicenna's" "canon" in 1242 in which he provided the first known accurate description of pulmonary circulation as it is known today. ibn al-nafis made two key improvements on galen's ideas of pulmonary circulation. first, he disproved the existence of the pores in the interventricular septum that galen had believed to allow blood flow between the left and right ventricles. second, he followed that the only way for blood to get from the right to the left ventricle in the absence of interventricular pores was pulmonary circulation. he also described the anatomy of the lungs in clear, correct detail, which his predecessors had not. however, like aristotle and galen, al-nafis still believed that the vital spirit was formed in the left ventricle from a mixture of blood and air. despite the enormity of ibn al-nafis's improvements on the theories of pulmonary circulation that preceded him, his commentary on "the canon" was not widely known to western scholars until the manuscript was discovered in berlin, germany, in 1924. as a result, ibn al-nafis was not widely credited with the discovery of pulmonary circulation in western medical literature until recently.