Final answer:
Layers of compact bone are referred to as external and internal lamellae, which are part of the osteon structure in compact bone providing strength and rigidity.
Step-by-step explanation:
The layers of compact bone mentioned are called external and internal lamellae. Compact bone, also known as cortical bone, provides the rigid structure and strength bones need. It is found on the outer layer of all bones and surrounds the medullary cavity, which contains the bone marrow. The structural units of compact bone are called osteons, or Haversian systems.
Each osteon is made up of concentric layers of calcified matrix, known as the lamellae, and in the center of each osteon is the Haversian canal, which hosts blood vessels, nerves, and lymphatic vessels. The lamellae play an essential role in the bone's ability to withstand stress and prevent fractures. Between the lamellae lie small cavities called lacunae, which house osteocytes, or bone cells. The lacunae are interconnected by a network of tiny canals called canaliculi, enabling the distribution of nutrients and waste removal.