The mouth, or buccal cavity, and its extension, which stretches through the body to the anus, is not listed as an internal body cavity. Why?© BrainMass Inc. brainmass.com October 9, 2019, 4:01 pm ad1c9bdddf
Because technically, it's not "internal" to the body. It's "external" to the ...
This solution explains why the buccal cavity is not considered internal.