Leonardo's formal training in the anatomy of the human body began with his apprenticeship to Andrea del Verrocchio, his teacher insisting that all his pupils learn anatomy. As an artist, he quickly became master of topographic anatomy, drawing many studies of muscles, tendons and other visible anatomical features.
As a successful artist, he was given permission to dissect human corpses at the Hospital of Santa Maria Nuova in Florence and later at hospitals in Milan and Rome. From 1510 to 1511 he collaborated in his studies with the doctor Marcantonio della Torre and together they prepared a theoretical work on anatomy for which Leonardo made more than 200 drawings. It was published only in 1680 (161 years after his death) under the heading Treatise on painting.
Leonardo drew many studies of the human skeleton and its parts, as well as muscles and sinews, the heart and vascular system, the sex organs, and other internal organs. He made one of the first scientific drawings of a fetus in utero. As an artist, Leonardo closely observed and recorded the effects of age and of human emotion on the physiology, studying in particular the effects of rage. He also drew many figures who had significant facial deformities or signs of illness.
He also studied and drew the anatomy of many other animals as well, dissecting cows, birds, monkeys, bears, and frogs, and comparing in his drawings their anatomical structure with that of humans. He also made a number of studies of horses.