Source : Webster's Revised Unabridged Dictionary (1913)

Endoskeleton \En`do*skel"e*ton\, n. [Endo- + skeleton.] (Anat.)
   The bony, cartilaginous, or other internal framework of an
   animal, as distinguished from the exoskeleton.

Source : WordNet®

endoskeleton
     n : the internal skeleton; bony and cartilaginous structure
         (especially of vertebrates)