"Osteocytes and layers of extracellular matrix, which are concentrically clustered around a central canal, for a cylinder-shaped unit are called ."

Osteon

Explanation:

Bone tissue may be of two types; compact bone tissue that form the outer hard covering of bones and spongy bone tissue that form inner soft portion of bone. Osteon are found in compact bone.

Osteons are cylindrical structures composed from clustre of Osteocytes and layers of extracellular matrix around a central canal connected by canaliculi for the transportation of blood. The haversian canal is surrounded by lamella that comprises the osteon. Osteons run parallel to long axis of bones and present in bones of many mammals, reptiles and birds. In some bones the stress or pressure in applied from few directions and osteons are aligned in that direction so they provide protection from bone bending or fracturing from compressive forces.