May 1, 2014: I accessed the WildEarthTV archives of the Delta Bald Eagle Nest and found this excellent close-up of one of the Delta 2 Eagles. One can get a good look at the tongue and the glottis.
"The tongue of a bird is extremely sensitive, filled with tactile sensory corpuscles. Two features we could see were the hole in the tongue and the backward facing barbs. The hole in the tongue is the "glottis" which is the entrance to the larynx and trachea which is known as the windpipe. The glottis closes during swallowing. The barbs are called "rear-directed papillae" and aid in the swallowing of food."
Source: CCB Eagle Nest Blog (The Center for Conservation Biology)