Classification of Bones

The adult human skeleton typically comprises 206 bones, which are primarily classified on the basis of shape as long, short, flat, and irregular.

Long bones are cylindrical and longer than they are wide. Most bones in the limbs, such as the femur, humerus, and finger bones, are of this type.

In contrast, short bones have a cube-like appearance, with roughly equal sides. The carpals of the wrist and tarsals of the ankle are examples of  short bones.

Sesamoid bones are similar to short bones but are more rounded and flatter and are embedded within tendons or muscles. The patella, or kneecap, is a sesamoid bone found at the knee joint.

The third type is flat bones, exemplified by the scapulae, sternum, and bones of the skull. They are thin, and plate-like, and though termed flat, are usually curved.

Lastly, bones with complex shapes are classified as irregular bones. For example, the vertebrae and facial bones have flat surfaces, arches, and multiple processes that give them a composite, irregular shape.