On long bones, such as those in the arms and legs the large expanded portions are called epiphyses. These are the regions of the bones that articulate with other bones. The shaft of the bones between the epiphyses is called the diaphysis. Except of the articular cartilage which covers the epiphyes the entire bones is covered in a tough, vascular tissue called periosteum. Periosteum fibers interlock with fibers of tendons and muscles that are connected to the bone. The wall of the diaphysis is composed of a strong, tightly packed, bend resistant tissue called compact bone. The epiphyses, on the other hand, is formed mostly by spongy bone. Spongy bone is made of many small bone plates that have irregular interconnected spaces that help keep bones light but very strong. The compact bone in the diaphysis of long bones form a tube or channel called the medulary cavity. This cavity is continuos through the length of the diaphysis and then fades into the spongy bone. The medulary cavity is filled with a special type of soft connective tissue called marrow.
In bone, as in all connective tissues, the fundamental constituents are the cells and the extracellular matrix. The latter is particularly abundant in this tissue and is composed of collagen fibers and non-collagenous proteins. The matrix of bone, as well as the matrices of cartilage and the tissues forming the teeth, however, has a unique ability to become calcified.
Anatomically, there are two types of bones in the skeleton:
1) Flat bones include the skull, scapula, mandible, and ileum
2) Long bones include the tibia, femur, and humerus.
The osteoclast is the bone lining cell responsible for bone resorption.