Page 'Breadcrumb' Navigation:
About Bone
Bone makes up the skeleton of all vertebrates, including humans. It is a hard connective tissue consisting of cells embedded in a matrix of mineralized ground substance and collagen fibers. By weight, bone is composed of 65–75% inorganic and 25–35% organic material. The inorganic component is composed of calcium phosphate (85%), calcium carbonate (10%) and magnesium. In humans, there are approximately 200 distinct bones in the skeleton, not including the auditory ossicles of the tympanic cavity or the sesamoid bones other than the two patellae. Bone is enveloped by a fibrous membrane, periosteum that covers the bone's entire surface except for the articular cartilage. Beneath the periosteum is a dense layer, compact bone, and beneath that a cancellous layer, spongy bone. The core of a long bone is filled with marrow.