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# 3.2. Structure of Bones A bone's structure develops as it ossifies. A long bone, when cut open in the diaphysis, displays the following structure (Figure 41A): * **Periosteum**: Protective membrane. * **Compact bone tissue layer**. * **Endosteum**: Inner bone layer. * **Medullary cavity...

# 3.2. Structure of Bones A bone's structure develops as it ossifies. A long bone, when cut open in the diaphysis, displays the following structure (Figure 41A): * **Periosteum**: Protective membrane. * **Compact bone tissue layer**. * **Endosteum**: Inner bone layer. * **Medullary cavity**: Contains yellow bone marrow. If the cut is through the epiphysis (Figure 41A), the following is observed: * **Periosteum**. * **Articular cartilage**: Thin layer of compact bone tissue. * **Spongy bone tissue**: With the marrow located internally. In a flat bone (Figure 41B): * **Periosteum**. * **Compact bone tissue**. * **Spongy bone tissue**. * **Compact bone tissue**. * **Periosteum**. ## Periosteum The periosteum is a connective tissue membrane tightly bound to the bone (Figure 41). It contains blood vessels, lymphatic vessels, and nerve endings that extend into the bone through openings and channels. The periosteum plays a role in bone growth, repair, and nutrition. * The outer fibrous layer of the periosteum is connected to ligaments and tendons. * The inner layer, called the osteogenic layer, is rich in osteoblasts (bone-forming cells). These cells are crucial in bone repair. (Figure 42). ## Compact Bone Compact bone, as the name implies, is dense and strong. Despite its density, it has many small holes, channels, and spaces (Figure 43). * Blood vessels, specifically capillaries and arterioles, pass through these openings. * The channels that penetrate the bone are called Haversian canals and Volkmann's canals. They contain blood vessels that supply nutrients and oxygen to bone cells. (Figure 43)