How did Ibn al-Nafis and Servetus anticipate part of William Harvey’s discovery?

Both Ibn al-Nafis and Michael Servetus anticipated a portion of William Harvey’s discovery by describing what is known as the "lesser circulation" of blood.1

• Ibn al-Nafis: In the 13th century, this Arab physician correctly identified that blood must pass from the right ventricle of the heart to the left ventricle by way of the lungs. He reached this conclusion by observing that the wall separating the heart's ventricles is solid and lacks the pores previously theorized by Galen, thereby disputing the idea that blood passed directly between the two sides.12
• Michael Servetus: In the 16th century, the Spanish physician independently described this pulmonary circulation, noting that blood travels from the heart to the lungs and back.13

While these thinkers recognized that blood circulated between the heart and lungs, they did not describe the full systemic circulation of blood throughout the entire body, which was William Harvey's definitive achievement.1