Plastron

In the anatomy of turtles (including s and s), the plastron is the smaller, flatter part of a turtle shell, and together with the carapace is an integral part of a turtle's ekeleton. In an ordinary turtle, the plastron is the bottom part of the shell. In a humanoid mutant turtle, the plastron comprises the turtle's chest and abdominal region, and depending on the comic or television series (or artist), can also appear muscular.