Categorizing Bones by Shape


The bones of the human skeleton can be classified according to their general shape. Figure 6.1 shows the six major categories commonly used.

Long bones are longer than they are wide and usually contain a central shaft flanked by wider heads at either end. The shaft of a long bone is its diaphysis (die-AFF-ih-sis) and each end is called an epiphysis (eh-PIFF-ih-sis). Long bones can be quite long, like the femur (thigh) bone, or quite short, like the phalanx (finger and toe) bones.

Short bones are typically about as wide as they are long. They are only found in the hands and the feet. The carpal bones around the wrists and the tarsal bones around the ankle are all short bones.

Flat bones are broad and quite thin. They usually serve a protective function, like the bones of the skull or the ribs.

Sesamoid bones are circular bones, reminiscent of sesame seeds in shape, that are always found embedded in tendons at joints. The patella (or knee cap) is the largest and best-known sesamoid bone.

Irregular bones are ones whose shapes do not fit neatly into the long, short, flat, or sesamoid bone categories. They include most of the bones of the skull and the bones of the vertebral column.

Sutural bones are only found in the skull. They are the small islands of bone that form if two of the major cranial bones do not completely join during the formation of the cranial sutures in the first months of a baby’s life.  Their number and locations vary from individual to individual. As a result, these are the only bones in the human body that don’t have individual names. They are also known as intra-sutural bones or Wormian bones.


Figure 6-1. The six different ways to classify bones by shape.



Lab 6 Exercises 6.1

  1. The instructor will provide you with several bones from the human body. For each one, identify which shape category it belongs to and give the reasons why it belongs to that category.
Bone Shape Category Reasons for categorization