skeleton /skel′ətən/ [Gk, skeletos, dried up] , the supporting framework for the body, comprising 206 bones in the adult that protect delicate structures, provide attachments for muscles, allow body movement, serve as major reservoirs of blood, and produce red blood cells, platelets, and most white blood cells. The skeleton is divided into the axial skeleton, which has 74 bones; the appendicular skeleton, with 126 bones; and the 6 auditory ossicles. The four types of bones composing the skeleton are the long bones, including the humerus, the ulna, the femur, the tibia, the fibula, and the phalanges of the fingers and the toes; the short bones, including the carpals and the tarsals; the flat bones, including the frontal bone and the parietal bone of the cranium, the ribs, and the shoulder bones; and the irregular bones, including the vertebrae, the bones of the sacrum, the bones of the coccyx, and certain bones of the skull, such as the sphenoid, the ethmoid, and the mandible. The skeleton changes throughout life as bone formation and bone destruction proceed concurrently. During childhood and adolescence, bone formation proceeds faster than bone destruction. Starting at 35 to 40 years of age, bone destruction proceeds faster than bone formation. In advanced age bone destruction increases, bones become thin and brittle, vertebrae may collapse, and height decreases. See also bone. −skeletal, adj.
