Astanga Hrudaya
गर्भस्य नाभौ मातुश्च हृदि नाडी निबध्यते । यया स पुष्टिमाप्नोति केदार इव कुल्यया ॥ ५६ ॥
Fetal circulation and nourishment to fetus: A tube connects the umbilicus of the fetus and the heart of the mother from which it ( fetus) derives nourishment just like a cornfield from the aqueduct.
english translation