What is tortoise shell made from?

"There are two parts to the shell of a turtle: the upper portion is called the "carapace" and the bottom half is called the "plastron." Both shells are actually made of many fused bones. The carapace is the fusion of about 50 bones - the ribs and vertebrae. The plastron is the fusion of bones including the clavicles (collar bones), bones between the clavicles, and portions of the ribs. A bony bridge joins the carapace and the plastron along the side of the turtle. Some turtles have a moveable joint, usually in the plastron, which acts as a "hinge" and allows the turtle to pull the carapace and plastron together tightly, while the turtle retracts its body into the shell. Shells have a blood and nerve supply, so bleeding and pain can result if the shell is"

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