Note how the nuclei are present near the surface of these muscle 'fibers'. Same preparation as for 12. Same preparation as for 12. Haversian system in adult mammalian bone. A blood vessel enters the Haversian canal at the cylinder center.
Bone remodels constantly during life and the Haversian system is evidence of bone remodeling.
See the Tissues lab write-up for how this development occurs, and keep in mind that because bone matrix is rigid, new bone can only be added to the surface of old bone. This addition to the surface is called appositional growth. See PJH for adult bone structure. E.g. PJH Fig. Since in modern vertebrates only warm blooded adults form Haversian systems, their presence in the fossil has been used to argue that dinosaurs were warm blooded.