What is Bone?
{{for|the television series|Bones (TV series)}} {{Infobox anatomy |Name = Bone |image = Foot bones.jpg |caption = The ''bones'' of a human [[foot]] }} '''Bones''' are parts of the [[skeleton]] of [[vertebrate]]s. They also protect [[Organ (anatomy)|organs]] inside our body.<ref name=firstbody>{{cite book|url=https://books.google.com/books?id=weyXAAAACAAJ|title=My First Book on the Human Body|publisher=Robert Frederick|location= Bath|date=2004|isbn=0-7554-3506-0|accessdate=13 July 2010|language=}}</ref> The bones are the [[framework]] of the [[body]]. Without them we would be a pile of organs and [[skin]] on the ground and would not be able to move. Bones also protect us. The [[skull]] protects the [[brain]] and the [[rib cage|rib]]s protect the [[heart]] and [[lung]]s. The [[jaw]] and [[skull]] support the facial muscles, which help us eat and move our mouth. The [[pelvis]] protects the reproductive organs, and [[vertebrae]] protect the [[spinal cord]]. Bone is living tissue, and must be maintained by taking regular [[exercise]] and by having [[calcium]] from foods like [[milk]], and dark leafy greens such as [[spinach]]. The [[bone marrow]] in the middle of the bigger bones makes our [[red blood cell]]s. == Structure == === Bone marrow === Long bones are hollow, with a central core which is not strong like the rest of the bone. It contains the [[bone marrow]], one of the most important [[tissues]] in the vertebrate body. It produces [[blood cells]] for the blood system, and [[lymphocytes]] for the [[immune system]]. {{-}} [[File:Illu compact spongy bone.jpg|500px|center|thumb|Diagram of a typical long bone: shows compact (cortical) and cancellous (spongy) bone]] === Osteons === [[File:Transverse section of bone en.svg|thumb|right|300px|microscopic bone structure]] Osteons are the small units of which the hardest parts of human bones are made. They are roughly cylindrical, and about 0.2mm wide and a few millimeters long. They are found in the bone in most [[mammals]], and many [[reptiles]], [[birds]] a