It is believed all snakes came from lizards. Monitors, of the old world, Africa, Asia, and Indo-Australia, (genus varanus), and tegus, the new world equivalent, (genus tupinambis), are the closest lizards currently still alive, to snakes. They have forked tongues that deliver molecules in the air to their jacobson's organ to "taste" the scent in the air, similar to snakes. And they move in a very similar "slithering" manner, albeit with legs. And all can swallow whole prey in a manner similar to a snake, though most will eat carrion as well as smaller prey such as insect and fish.
And the snake families pythoninae & boidae both have vestigial hind limbs, the "spurs" on either side of the cloaca. There are some other snakes that have them as well, but these two families are most often cited as the most primitive snake families left.
