noun
endoskeleton
Biological term for an internal skeleton, as in vertebrates. Contrasts with 外骨格 (exoskeleton).
See also: 外骨格
人間を含む脊椎動物は内骨格を持つ。
Vertebrates, including humans, have an endoskeleton.
外骨格 means 'exoskeleton', an external skeleton like that of insects or crustaceans, while 内骨格 is an internal skeleton.
Compound of 内 (nai, 'inside') + 骨格 (kokkaku, 'skeleton'). The reading こっかく is a regular rendaku-influenced form of 骨格.