Back of tongues
In the view of the tongue linked above I am looking at the root or back of tongue looking forward. The tongue lies above the epiglottis. It is always surprising to me how thick it is. I can see the greater cornu of the hyoid peaking out on the left side at the same height as mid epiglottis in this view. My understanding is that when I swallow the hyoid elevates and the epiglottis closes over the glottis preventing food from entering the airway.
I am trying to have the left tongue move forward relax and hollow while having the right tongue harden and come back. In doing so I feel the musculature and structures of the anterior throat trying to mirror the action. In the back I can feel changes all the way down the posterior spine to the pelvis. It feels like the use of my spine is a reflection of my tongues.