A long bone is a type of bone that is longer than it is wide, characterized by a shaft called the diaphysis and two ends known as epiphyses. These bones are primarily found in the limbs, such as the femur in the thigh and the humerus in the upper arm. Long bones are essential for movement and support, as they act as levers for muscles. Long bones are composed of a dense outer layer called cortical bone and a spongy inner layer known as trabecular bone. They contain a central cavity, the medullary cavity, which houses bone marrow, responsible for producing blood cells. The structure of long bones allows them to withstand significant forces and provide stability to the skeletal system.