Yoga Sutra 3.31 on the tortoise nerve, rigid steadiness
Sūtra III. 31 On the tortoise nerve, rigid steadiness Below the throat-pit, in the chest, is a nerve-channel called the Tortoise. Having made saṃyama on it, he attains a state of rigid steadiness, like that of a snake or lizard (when gripped). Below the throat-pit, in the chest, is a nerve-channel called the Tortoise. Having…