The braincase of most plesiomorphic sarcopterygians is divided by the intracranial point into ethmosphenoid and otic-occipital portions each covered by dermal bones. The function of the joint is presumably to increase the gape of the mouth rapidly during opening phases. (Forey 1997) [ https://www.worldcat.org/search?q=bn%3A978-0-412-78480-4 ]