Musar zu Tehillim 104:3

Just as man in a little way is like God, so is the structure of his body like all the world. He made the dome of his head like the expanse of the upper heavens. He made the roof of his mouth in which are planted the teeth and molars, like those heavens which are above us. And just as this lower heaven which is over us separates the upper waters from the lower waters, so does the roof of the mouth divide between the moisture of the mouth and between the moisture of the head and between the moisture of the upper crust. And just as God as caused His Divine Presence to dwell in the upper heavens which He spread over the waters, as it is written, "Who layest the beams of thine upper chambers in the waters" (Ps. 104:3), so has He caused the spirit of the soul of life and knowledge and understanding to dwell in the crust of the head which forms a crust around the brain and its moisture. And observe and understand the truth, that if the crust of the brain should be torn or pierced then the man would die at once because in it dwells the spirit of life.