Bones consist of different types of tissue, including compact bone, spongy bone, bone marrow, and periosteum. Compact bone makes up the dense outer layer of bone. It is very hard and strong. Spongy bone is found inside bones and is lighter and less dense than compact bone. This is because spongy bone is porous. Bone marrow is a soft connective tissue that produces blood cells. It is found inside the pores of spongy bone. Periosteum is a tough, fibrous membrane that covers and protects the outer surfaces of bone.3
