Here Leonardo records his initial understanding of conception, as derived from the writings of earlier anatomists and philosophers. The two bodies are presented as if sectioned down the middle, though Leonardo could never have seen such an arrangement. In the man Leonardo has drawn tubes passing into the penis from the spinal cord (to transmit an ‘animal’ or ‘soul’ element), from the heart (a ‘spiritual’ element), and from the testes (a ‘material’ element). In the woman, a branch of the spinal cord likewise transmits her ‘animal’ element to the uterus. A vessel also travels from the uterus to the breast, to allow the menses retained during pregnancy to be converted into milk.