squelette

Squelette is the French word for skeleton, the internal or external framework that gives shape and protection to an animal. In biology, skeletons vary by lineage and are commonly categorized as endoskeletons, exoskeletons, or hydrostatic skeletons.

Endoskeletons are internal structures of bone and cartilage, as in vertebrates. They support the body, protect organs, and act as levers for muscles. The vertebrate skeleton has axial parts (skull, spine, rib cage) and appendicular parts (limbs and girdles). Bones are living tissue with minerals and collagen and contain marrow that produces blood cells. Growth occurs by ossification and remodeling continues through life.

Exoskeletons are outer shells found in many arthropods and some mollusks. They provide protection and muscle attachment but limit growth, requiring periodic shedding and replacement (ecdysis). Exoskeletons are often made of chitin or calcium carbonate and may include joints and flexible membranes to allow movement.

Hydrostatic skeletons use fluid-filled cavities surrounded by muscles. Pressure changes within these compartments enable locomotion, as seen in many worms and other soft-bodied invertebrates. They do not rely on rigid bones, but on muscle contraction and body fluid pressure.

The skeleton stores minerals, supports soft tissues, protects organs, and, in many species, forms blood cells. In humans, it remodels with use and aging. Skeletal disorders include fractures, osteoporosis, and deformities. Imaging methods such as X-ray, CT, and MRI help diagnose conditions, while treatments range from immobilization to surgery and prosthetics.