Yōga Sūtra 3.30

नाभिचक्रे कायव्यूहज्ञानम्।

nābhicakrē kāyavyūhajñānam।

[नाभि चक्रे काय व्यूह ज्ञानम्।
nābhi = on naval; cakrē = center; kāya = physical body; vyūha = system; jñānam = knowledge;]

(By samyama) on the navel center, one gains the knowledge of the physical body system.