Crocodilians have a secondary bony palate that enables them to
breathe when partially submerged, even if the mouth is full of
water. Their internal nostrils open in the back of their throat,
where a special part of the tongue called the "palatal valve"
closes off their respiratory system when they are underwater. This
way they can open their mouths underwater without choking. Most
reptiles lack a secondary palate, but some skinks (family
Scincidae) have evolved a bony secondary palate too, to varying
degrees. Source: Wikipedia