Polarized light micrograph showing a transverse section of human compact bone. Concentric rings called lamellae surround Haversian canals that run parallel to the axes of long bones containing blood, lymphatic vessels, and nerves. The lamellae are made of compacted collagen fibers and ground substances produced by cells called osteoblasts. During bone formation osteoblasts become trapped in the bone matrix at sites called lacunae, visible as small dark areas. POL 50x at 35mm.