Classification of Bones

CLASSIFICATION OF BONES

1. Long bones—the bones of the arms, legs, hands, and feet (but not the wrists and ankles). The shaft of a long bone is the diaphysis, and the ends are called epiphyses (see Fig. 6–1). The diaphysis is made of compact bone and is hollow, forming a canal within the shaft. This marrow canal (or medullary cavity) contains yellow bone marrow, which is mostly adipose tissue. The epiphyses are made of spongy bone covered with a thin layer of compact bone. Although red bone marrow is pres-ent in the epiphyses of children’s bones, it is largely replaced by yellow bone marrow in adult bones.

2. Short bones—the bones of the wrists and ankles.

3. Flat bones—the ribs, shoulder blades, hip bones, and cranial bones.

4. Irregular bones—the vertebrae and facial bones.

Figure 6–1. Bone tissue. (A) Femur with distal end cut in longitudinal section. (B) Compact bone showing haversian systems (osteons).

QUESTION: What is the purpose of the blood vessels in bone tissue?

Short, flat, and irregular bones are all made of spongy bone covered with a thin layer of compact bone. Red bone marrow is found within the spongy bone.

The joint surfaces of bones are covered with artic-ular cartilage, which provides a smooth surface. Cov-ering the rest of the bone is the periosteum, a fibrous connective tissue membrane whose collagen fibers merge with those of the tendons and ligaments that are attached to the bone. The periosteum anchors these structures and contains both the blood vessels that enter the bone itself and osteoblasts that will become active if the bone is damaged.