Bones

Long bones

These bones develop via endochondral ossification, a process in which the hyaline cartilage plate is slowly replaced. A shaft, or diaphysis, connects the two ends known as the epiphyses (plural for epiphysis). The marrow cavity is enclosed by the diaphysis which is thick, compact bone. The epiphysis is mainly spongy bone and is covered by a thin layer of compact bone; the articular ends participate in the joints.

The metaphysis is situated on the border of the diaphysis and the epiphysis at the neck of the bone and is the place of growth during development. This group of bones includes the: 

• humerus
• ulna
• radius
• fibula
• tibia
• femur
• metacarpal bones
• phalanges

Short bones

A thin external layer of compact bone covers vast spongy bone and marrow, making a shape that is more or less cuboid. The carpal bones and tarsal bones fall into this category.

Flat bones

Two layers of compact bone cover both spongy bone and bone marrow space. They grow by replacing connective tissue. Fibrocartilage covers their articular surfaces. This group is compiled of the:

• skull bones
• ribs
• sternum
• scapulae

Irregular bones

A thin layer of compact bone covers a mass of mostly spongy bone. This group is not categorized by shape, but by bone content and includes the

• bones of the skull
• vertebrae
• coxa

Sesamoid bones

Sesamoid bones are embedded within tendons. They are found at the end of long bones in the limbs, where the tendons cross, for example the patella bone in the knee. Sesamoid bones protect the tendons from excess wear by reducing friction.