Spongy bone

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Bone is the basic unit of the human skeletal system.

Bone tissue is generally classified as compact or spongy bone. Compact bone forms the hard outer layer of bone while spongy bone forms the porous interior. 

Spongy bone, also known as cancellous bone, is composed of a lattice-like arrangement of osteocytes known as trabeculae. Trabeculae form a mesh-like network of bony spicules of varying size that are aligned along regions of biomechanical stress. They project into the medullary cavity from the internal circumferential lamellae of the cortical bone. The trabecular network of spongy bone aids in reducing bone weight and density and functions to transfer force from the articular surface of cortical bone.

Due to its cancellous nature, spongy bones are typically present in bones which are not heavily stressed or in regions of bone with multiple stress directions such as the neck of the femur. Spongy bone is commonly found at the end of long bones, as well as the ribs, skull, pelvic bones and vertebrae. 

Located in the spaces, between the trabeculae of some spongy bones is red bone marrow. Blood vessels within red bone marrow supply osteocytes of spongy bone and aid in removing waste products. Red bone marrow also forms the site for hematopoiesis.