The Da Vinci Notebooks
On corpulency and leanness (809-811).Make the rule and give the measurement of each muscle, and give the reasons of all their functions, and in which way they work and what makes them work &c
[4] First draw the spine of the back; then clothe it by degrees, one after the other, with each of its muscles and put in the nerves and arteries and veins to each muscle by itself; and besides these note the vertebrae to which they are attached; which of the intestines come in…