![]() ![]() The skeleton is subdivided into two divisions: the axial skeleton, the bones that form the longitudinal axis of the body, and the appendicular skeleton, the bones of the limbs and girdles. Blood cell formation, or hematopoiesis, occurs within the marrow cavities of certain bones. Fat is stored in the internal cavities of bones bone itself serves as a storehouse for minerals, the most important of which are calcium and phosphorus because most of the body’s calcium is deposited in the bones as calcium salts, the bones are a convenient place to get more calcium ions for the blood as they are used up. Skeletal muscles, attached to bones by tendons, use the bones as levers to move the body and its parts. ![]() Bones protect soft body organs for example, the fused bones of the skull provide a snug enclosure for the brain, the vertebrae surround the spinal cord, and the rib cage helps protect the vital organs of the thorax. ![]() Bones, the “steel girders” and “reinforced concrete” of the body, form the internal framework that supports the body and cradle its soft organs the bones of the legs act as pillars to support the body trunk when we stand, and the rib cage supports the thoracic wall. Types of Synovial Joints Based on Shapeīesides contributing to body shape and form, our bones perform several important body functions.The skull reaches its definitive size around the 20 th year of life.Although the word skeleton comes from the Greek word meaning “dried-up body”, our internal framework is so beautifully designed and engineered that it puts any modern skyscraper to shame. Most features of the adult skull appear during the first two years of life, including the inner and outer tables, diploic space, vascular markings, and grooves for the dural sinuses. ![]() During birth, the sutures and fontanels overlap (molding) to aid the head's passage through the birth canal. The posterior fontanel closes before the age of 3 months and may already be closed at birth, while the anterior fontanel closes after the age of 18 months this is of prime importance for performing cranial ultrasound. two posterolateral (or mastoid) fontanelles.two anterolateral (sphenoidal) fontanelles.In addition to the sutures, there are six fontanelles (also spelled fontanels) which are six flat membranous junctions where three or four sutures meet: The sagittal suture develops from neural crest cells and the coronal suture, from paraxial mesoderm. The plates are separated by broad dense connective tissue seams, the sutures. The calvarial bones form within a collagen matrix as bone spicules, which radiate from a primary ossification center in each bony plate toward the periphery. The mesoderm undergoes direct intramembranous ossification from which the flat calvarial bones are formed, that is to say, there is no intervening cartilaginous scaffolding. The membranous neurocranium develops from paraxial mesoderm and neural crest cells. The cranial vault develops from the membranous neurocranium. the interparietal part of the occipital bone.the squamous part of the paired temporal bones.The cranial vault consists of the following flat bones: ![]()
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