What does endoskeleton mean?
An endoskeleton is the internal framework of bone or cartilage that supports and protects the body of an animal, most familiarly in vertebrates such as fish, birds, reptiles, and mammals, including humans. Unlike an exoskeleton — the hard external shell found in insects and crustaceans — an endoskeleton grows along with the organism, so it does not need to be periodically shed and replaced. It provides attachment points for muscles, shields delicate internal organs such as the brain and heart, and enables large, active bodies that external armor could never support. The word is chiefly used in scientific and educational contexts, often appearing alongside its counterpart 'exoskeleton' when biologists compare structural designs across the animal kingdom. Sharks illustrate one variant: their endoskeletons are made of cartilage instead of bone. For general readers, it is a useful precise term whenever the discussion turns to how bodies are built and held upright.
nounAn internal framework of bone or cartilage that supports the body of an animal, such as a vertebrate, in contrast to an external skeleton.
- The internal framework of bone or cartilage that gives structural support to the bodies of vertebrates and some other animals.
"Unlike insects, whose hard shell lies outside the body, humans rely on an endoskeleton for support and protection."
"The shark's endoskeleton is made entirely of cartilage rather than bone."
"As vertebrates evolved, the endoskeleton allowed bodies to grow far larger than any exoskeleton could support."
Regular English plural; commonly used when comparing different species or groups of animals.
"Vertebrates and echinoderms both have endoskeletons, though their structures differ greatly."
Your bones are living scaffolding you carry inside you — and unlike a crab's shell, your endoskeleton grows with you instead of forcing you to molt out of it.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of endoskeleton
The word combines the Greek prefix 'endo-', meaning 'within' or 'inside', with 'skeleton', which derives from the Greek 'skeletos', meaning 'dried up', a reference to the dried, hardened state of bones. It was coined in the nineteenth century as comparative anatomy developed the need to distinguish internal frameworks from external ones. The same 'endo-' element appears in related scientific terms such as 'endoderm' and 'endocrine'.
How endoskeleton is actually used
Endoskeleton is a technical term used mainly in biology, zoology, anatomy, and science writing rather than everyday conversation; it is typically discussed in contrast with 'exoskeleton' when classifying how animals are supported structurally.
Easily confused with endoskeleton
An exoskeleton is a rigid outer covering, as in insects and crustaceans, whereas an endoskeleton is an internal supporting framework, as in vertebrates.