Final answer:
Trabeculae are the structural features in spongy bone that align with stress lines and are extensively cross-braced, providing strength and reducing bone density for stress adaptation.
Step-by-step explanation:
The structural features of spongy bone that are oriented along stress lines and are cross-braced extensively are known as trabeculae. These trabeculae are arranged in such a way that they can bear different types of stresses, with one side handling tension, while the opposite side withstands compression. Trabeculae form a lattice-like structure that not only strengthens the bone along lines of stress but also makes the bone lighter, aiding in movement and providing space for bone marrow where hematopoiesis occurs. Bone matrix makes up both compact and spongy bone, with the latter having a structure that reduces bone density and allows for compression during stress.