Neidan Dictionary

⊛ Pierce through the Caudal Funnel, pass through the Muddy Pellet. 貫尾閭，通泥丸。 Comm. Wang Jie: Slowly, ascending from the Caudal Funnel (weilü), [Breath] reaches the Muddy Pellet, and the conjunction [of Breath and Spirit] occurs. 從尾閭徐徐提起，直上泥丸交姤。 Mirror for Compounding the Medicine, poem 12)

⊛ The upper Cinnabar Field, which is located at the top of the head, is also called Palace of the Muddy Pellet (niwan gong). Since the body is a microcosm, and the head corresponds to Heaven, the alchemical masters call it Palace of Qian ☰ (qiangong), with reference to the trigram that represents Heaven. When the practice reaches the stage of “refining the Essence to transmute it into Breath”, this Opening is the place where one “reverts the course of the Essence to replenish the brain” (huanjing bunao) and “eliminates the ore to keep the gold” (qukuang liujin). When it reaches the stage of “refining the Breath to transmute it into Spirit”, it is the point where the Yang Spirit (yangshen) rises. (Wang Mu, Foundations of Internal Alchemy, p. 25)

⊛ Where exactly is the Palace of the Muddy Pellet? In the head there are nine palaces. The central one is called Muddy Pellet. 問曰，泥丸宮正在何處。答曰，頭有九宮，中曰泥丸。 (Xiao Tingzhi, Questions and Answers on the Golden Elixir, trans. in Taoist Internal Alchemy: An Anthology of Neidan Texts, pp. 143-144)

⊛ When Breath transmutes itself and becomes Spirit, this Spirit dwells in the Muddy Pellet, which is its own Palace. 鍊氣化為神，神居泥丸為本宮。 (Wang Jie, comm. to Mirror for Compounding the Medicine, poem 12)