D15: Spongy bone and bone marrow. Spongy bone is also termed cancellous bone. It allows for light weight, without the sacrifice of much support. Spongy bone is composed of thin interconnecting trabeculae (arrowhead) with much intervening space. This space is filled by bone marrow and fat cells(*). Here, some spicules or trabeculae are also cut in cross-section; they stain the darkest. Note the lamellae within each trabeculum.