Spongy bone lacks the functional tube-like units called osteon found in compact bone. Osteon are formed by a network of small canals along with osteocyte cells lined up in rings around the canals. They are responsible for providing a channel for blood vessels, veins and nerves.
Spongy bone consists of a network of irregularly shaped sheets and spikes of bone. It is less dense and more flexible than compact bone, reducing the weight of the skeleton. Although it resembles a kitchen sponge under the microscope, spongy bone is solid and hard. Depending on the age of the person, spongy bone contains either red or yellow marrow.