Yes they can - as can all snakes. A snakes jaws are composed of sections (two in the lower jaw, and six in the upper jaw) connected by ligaments. This enables them to 'dislocate' their jaws to allow them to swallow large prey animals.
The question what is the biggest snake can be confusing, the biggest as far as girth is the Green Anaconda, on average anacondas are more then 20 ft long many reaching lengths of 29ft or more, with a...