Diagram of a typical long bone showing both compact (cortical) and cancellous (spongy) bone.<unk> s on cross-section of a bone The<unk>  or haversian system (named for Clopton Havers) is the fundamental functional unit of much compact bone.<unk> s are roughly cylindrical structures that are typically between 0.25 mm and 0.35 mm in diameter. Their length is often hard to define, but estimates vary from several millimeters to around 1 centimeter. They are present in many bones of most mammals and some bird, reptile, and amphibian species.
Osteon
Osteoid
Sesamoid bone
Osteotome
Epiphyseal plate
Fibrous cap
Sawbones 
Metacarpal bones