Sublime

The ratio of cortical to spongy bone is dependent upon the stresses applied to the bone: Bones that are exposed to high bending forces, such as the metatarsals of your forefoot, are made almost exclusively of cortical bone (A). In contrast, bones that absorb shock, such as your calcaneus (B), are made primarily of soft spongy bone, which allows the

The most superficial layer of the bone is a thin covering of connective tissue called periosteum. This periosteum contains nerves that sense pressure. This is how you know you have banged your shin bone into something. Blood enters bones through blood vessels that flow through the periosteum.

In fact, no bones in the living body are stacked. In a healthy body the bones do not touch each other.

Cortical bone, which is surrounded by the pain-sensitive periosteum, is extremely powerful and resists bending forces like a steel pipe. In contrast, spongy bone is softer and is loaded with small chambers that allow for the production of red blood cells.

(which protects the ends of bones)

There is also an opening in the body to allow for nourishment from the blood supply. Remember, bones are living tissue and, as such, need oxygen and other nourishment.