How do turtles stretch out their necks?

Their shells are actually an extension of their body, so they can't crawl out of their shell. The shell is anchored by the ribs on the inside of the shell. It's made of keratin, which is the same stuff that hair, nails and horns are made of. Inside that shell, a turtle's body is very muscular and is suspended from the ribcage. A turtle's neck can form a s-shape either sideways or vertically. When a turtle wants to pop his head in and out, they either fold their neck sideways or fold it long ways and upwards.