The Upaniṣads — the philosophical core of the Vedic tradition, revealing the nature of Brahman, the Ātman, knowledge, action and liberation. The ten principal Upaniṣads together with select minor Vaiṣṇava Upaniṣads.
Ancient embryology: how the body forms month by month, what it is made of, and how much of each. Its most famous passage is the cry in the womb: the child remembers everything and promises to remember — and forgets it all at birth.