Each haversian canal is surrounding by varying number ( 5-20 ) of concentrically arranged lamellae of bone martix.
The canals and the surrounding lamellae ( 8-15 ) form the functional unit, called a haversian system or osteon.
Within the bone itself, the haversian canals become blocked with scar tissue, and the bone becomes surrounded by thickened periosteum.
Haversian canals are contained within osteons, which are typically arranged along the long axis of the bone in parallel to the surface.
With otospongiosis, the normally dense enchondral bone is replaced by haversian bone, a spongy and vascular matrix that results in sensorineural hearing loss due to compromise of the conductive capacity of the inner ear ossicles.
However, it is generally agreed that endothermy first evolved in non-mammalian synapsids such as dicynodonts, which possess body proportions associated with heat retention, high vascularised bones with Haversian canals, and possibly hair.
In the group of malignant small round cell tumors which include Ewing's sarcoma, bone lymphoma, and small cell osteosarcoma, the cortex may appear almost normal radiographically, while permeative growth occurs throughout the Haversian channels.