From Kaushitaki Upanishad - Order of senses

Prâna (breath) is Brahman, thus says Paiṅgya. 
And in that prâna, which is Brahman, the eye stands firm behind speech, 
the ear stands firm behind the eye, 
the mind stands firm behind the ear, 
and the spirit stands firm behind the mind 

It is fantastic how the order of the gradation of the energy is by the shape of the face.

The Mouth is right ahead and therefore speech is the most gross/least conscious
After that is Sight. The eye situated behind speech. 

Then the Ear. So conscious Listening is a key practice.

Then the Mind that is behind even listening. So it can watch everyone.

Then the Spirit who can watch even the Mind. 

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Its so simple and right in front of our eyes !