First sign of Leonardo's actual practical involvement in anatomy and dissection is some wonderful, slightly eerie drawings of a skull, dateable to about 1489. One of the drawings makes it clear that at least one of his interests is to establish by a sort of grid-referencing, the particular location of the Ssensus communis which is an Aristotelian concept, the communal sense where all the sensory impressions go into the brain and which, was where a man's soul could be found.
Leonardo's first dissections were in search of the soul. His guide: a newly published manual of anatomy by Mondino de Liuzzi, which would remain the authority for 250 years. Even though he was a mechanical genius, he never treated the body as a machine. He said that nature has given the body, or has given animals, mechanical instruments.
But the source of the movement comes from the soul, which is not mechanical, which is spiritual, and by that he meant immaterial, and he actually traced back the sensory nerves to the centre of the brain, which he considered to be the seat of the soul.
In the centre of the brain, he found three small cavities, the ventricles.
The site, he was certain, of Aristotle's sensus communis.
Et ex consequenti in ventriculis eius. Substantia eius est substantia medullaris frigida et humida The soul appears to reside in the judicial part and the judicial part seems to be the place where all the senses come together, the sensus communis . . . and the sensus communis is the seat of the soul. Zoroastro In medio vero huius est sensus communis While Leonardo's proof of Aristotle's theories has not stood the test of time, his anatomical drawings have never been surpassed. Sequential views suggest a cinema animation. And views from multiple angles provide a true three-dimensional understanding of the body's form. His images are never static but animated by a dynamic energy, and seem just on the verge of moving on their own. Leonardo's illustrations, as precise as his technical drawings of machines, were unequalled in accuracy until the photographic techniques of the 19th century. But they were never published in his lifetime.
They remained unknown and unpublished for more than 300 years.