Bone tissue comprises cortical bone and cancellous bone, although bones may also contain other kinds of tissue including bone marrow, endosteum, periosteum, nerves, blood vessels, and cartilage. In the human body at birth, approximately 300 bones are present.
Bone is a rigid body tissue consisting of cells embedded in an abundant hard intercellular material. Bone tissue makes up the individual bones of the skeletons of vertebrates. Its two principle components are collagen and calcium phosphate.
Bones are classified by their shape. They may be long (like the femur and forearm), short (like the wrist and ankle), flat (like the skull), or irregular (like the spine). Primarily, they are referred to as long or short. There are 206 bones in the adult human skeleton.