Snakes
A hundred million years ago limb reduction occurred among ancient lizards and resulted in the evolution of snakes (Suborder Serpentes) of which about 2300 species live today. They differ from lizards in the following respects: (1) the right and left halves of the lower jaw are not firmly united, instead they are connected by an elastic ligament; (2) there is no pectoral girdle; (3) a urinary bladder is absent; (4) the braincase is closed anteriorly; (5) the eyelids are fused over the eyes but a transparent window exists which allows the snake to see; and (6) no external ear openings exist.
Snake Anatomy

Lizard Anatomy
