Leonardo wished to examine every aspect of thehuman body, not just structural anatomy and physiology, but also the conception and the growth, the emotions, the nature of the senses and so on.
We leave the word to Leonardo himself, reflecting on the difficulties facing the anatomical draughtsman (around 1508-1510):
Though you may have a love for such things, you will perhaps be impeded by your stomach; and if it does not impede you, you will perhaps be impeded by the fear of living through the night hours in the company of quartered and flayed corpses, fearful to behold. And if it does not impede you, perhaps you will lock the good draughtsmanship which such a depiction requires; and even if tou have skill in drawing, it may not be accompanied by a knowledge of perspective, and if it were so accompanied, you may lack the methods of geometrical demonstration and of calculating the forces and strengths of the muscles; or perhaps you will lack patience so that you will not be diligent. Whether all these things were found in me or not, the 120 books composed by me will give the verdict, yes or no. In these I have been impeded neither by avarice nor negligence but only by time. Farewell.