CONNECTING TO RESPIRATION. “In the early fully terrestrial tetrapods, a transverse sheet of dermal bones has developed inferior to the braincase specifically in the roof of the mouth posterior to the internal naris and primary palate. This secondary hard palate configuration was probably the precursor in allowing permanent breathing to travel through the primary nose as inspiratory air would travel through a non-collapsible oral cavity before going to the trachea.”
http://www.wjgnet.com/esps/DownLoadFile.aspx?Type=Digital&SubType=2&DOI=10.5319%2Fwjo.v6.i2.33&FilePath=Pub%5C10.5319%5Cv6%5Ci2%5CWJO-6-33.doc