The sesamoid bones protect tendons by helping them overcome excessive forces but also allow tendons and their attached muscles to be more effective. Tendons are a dense connective tissue that connect bones to muscles and sesamoid bones form where a great deal of pressure is generated in a joint. Sesamoid BonesĪ sesamoid bone is a small, round bone that forms in tendons (sesamo- = “sesame” and -oid = “resembling”). Many bones of the face, particularly the jaw bones that contain teeth, are classified as irregular bones.

These bones tend to have more complex shapes, like the vertebrae that support the spinal cord and protect it from compressive forces.

Irregular BonesĪn irregular bone is one that does not have any easily characterized shape and therefore does not fit any other classification. Flat bones serve as points of attachment for muscles and often protect internal organs.

Examples include the cranial (skull) bones, the scapulae (shoulder blades), the sternum (breastbone), and the ribs. The term flat bone is somewhat of a misnomer because, although a flat bone is typically thin, it is also often curved. Short bones provide stability and support as well as some limited motion. The only short bones in the human skeleton are in the carpals of the wrists and the tarsals of the ankles. Short BonesĪ short bone is one that is cube-like in shape, being approximately equal in length, width, and thickness. Long bones function as rigid bars that move when muscles contract. Long bones are found in the upper limbs (humerus, ulna, radius) and lower limbs (femur, tibia, fibula), as well as in the hands (metacarpals, phalanges) and feet (metatarsals, phalanges). Keep in mind, however, that the term describes the shape of a bone, not its size. Long BonesĪ long bone is one that is cylindrical in shape, being longer than it is wide. Figure 6.2.1 – Classifications of Bones: Bones are classified according to their shape. Like other structure/function relationships in the body, their shapes and their functions are related such that each categorical shape of bone has a distinct function. The 206 bones that compose the adult skeleton are divided into five categories based on their shapes ( Figure 6.2.1).

Describe the function of each category of bones.

Classify bones according to their shapes.

By the end of this section, you will be able to:

Flat bone example