Spongy bone, also called cancellous or trabecular bone, is a porous tissue that forms the interior of bones, especially the epiphysis and metaphysis of long bones. It is surrounded by a layer of dense compact bone, creating a strong but lightweight bone structure. The spongy core comprises irregularly arranged, branched trabeculae that form a mesh-like network. Similar to the osteons of compact bone, the trabeculae also comprise concentric lamellae of calcified bone matrix. The lacunae, spaces between the lamellae, harbor osteocytes that are interconnected via narrow branching canals called canaliculi. The canals further open into the spaces between the trabeculae. These spaces are filled with red bone marrow and tiny blood vessels that provide nutrition to the osteocytes via the canaliculi. The trabecular network is dynamic, orienting its growth along the different stress lines to withstand pressure from different directions.