<P> Al - Biruni (973 - 1048) estimated the radius of the earth as 6339.6 km (modern value is c. 6,371 km), the best estimate at that time . </P> <P> In the cardiovascular system, Ibn al - Nafis in his Commentary on Anatomy in Avicenna's Canon was the first known scholar to contradict the contention of the Galen School that blood could pass between the ventricles in the heart through the cardiac inter-ventricular septum that separates them, saying that there is no passage between the ventricles at this point . Instead, he correctly argued that all the blood that reached the left ventricle did so after passing through the lung . He also stated that there must be small communications, or pores, between the pulmonary artery and pulmonary vein, a prediction that preceded the discovery of the pulmonary capillaries of Marcello Malpighi by 400 years . The Commentary was rediscovered in the twentieth century in the Prussian State Library in Berlin; whether its view of the pulmonary circulation influenced scientists such as Michael Servetus is unclear . </P> <P> In the nervous system, Rhazes stated that nerves had motor or sensory functions, describing 7 cranial and 31 spinal cord nerves . He assigned a numerical order to the cranial nerves from the optic to the hypoglossal nerves . He classified the spinal nerves into 8 cervical, 12 thoracic, 5 lumbar, 3 sacral, and 3 coccygeal nerves . He used this to link clinical signs of injury to the corresponding location of lesions in the nervous system . </P> <P> Modern commentators have likened medieval accounts of the "struggle for existence" in the animal kingdom to the framework of the theory of evolution . Thus, in his survey of the history of the ideas which led to the theory of natural selection, Conway Zirkle noted that al - Jahiz was one of those who discussed a "struggle for existence", in his Kitāb al - Hayawān (Book of Animals), written in the 9th century . In the 13th century, Nasir al - Din al - Tusi believed that humans were derived from advanced animals, saying, "Such humans (probably anthropoid apes) live in the Western Sudan and other distant corners of the world . They are close to animals by their habits, deeds and behavior ." In 1377, Ibn Khaldun in his Muqaddimah stated, "The animal kingdom was developed, its species multiplied, and in the gradual process of Creation, it ended in man and arising from the world of the monkeys ." </P>

What did the golden age of islam contribute to history