Development of The Skull
The skull is a complex structure; its bones are formed both by intramembranous and endochondral ossification. The skull roof, comprising the bones of the splanchnocranium (face) and the sides and roof of the neurocranium, is formed by intramembranous (or dermal) ossification, though the temporal bones are formed by endochondral ossification. The endocranium, the bones supporting the brain (the occipital, sphenoid, and ethmoid) are largely formed by endochondral ossification. Thus frontal and parietal bones are purely membranous. The geometry of the cranial base and its fossas: anterior, middle and posterior changes rapidly, especially during the first trimester of pregnancy. The first trimester is crucial for development of skull defects.
At birth, the human skull is made up of 44 separate bony elements. As growth occurs, many of these bony elements gradually fuse together into solid bone (for example, the frontal bone). The bones of the roof of the skull are initially separated by regions of dense connective tissue called "fontanels". There are six fontanels: one anterior (or frontal), one posterior (or occipital), two sphenoid (or anterolateral), and two mastoid (or posterolateral). At birth these regions are fibrous and moveable, necessary for birth and later growth. This growth can put a large amount of tension on the "obstetrical hinge", which is where the squamous and lateral parts of the occipital bone meet. A possible complication of this tension is rupture of the great cerebral vein of Galen. As growth and ossification progress, the connective tissue of the fontanelles is invaded and replaced by bone creating sutures. The five sutures are the two squamous, one coronal, one lambdoid, and one sagittal sutures. The posterior fontanel usually closes by eight weeks, but the anterior fontanel can remain open up to eighteen months. The anterior fontanel is located at the junction of the frontal and parietal bones; it is a "soft spot" on a baby's forehead. Careful observation will show that you can count a baby's heart rate by observing his or her pulse pulsing softly through the anterior fontanel.
Read more about this topic: Human Skull
Famous quotes containing the words development of, development and/or skull:
“And then ... he flung open the door of my compartment, and ushered in Ma young and lovely lady! I muttered to myself with some bitterness. And this is, of course, the opening scene of Vol. I. She is the Heroine. And I am one of those subordinate characters that only turn up when needed for the development of her destiny, and whose final appearance is outside the church, waiting to greet the Happy Pair!”
—Lewis Carroll [Charles Lutwidge Dodgson] (18321898)
“This was the Eastham famous of late years for its camp- meetings, held in a grove near by, to which thousands flock from all parts of the Bay. We conjectured that the reason for the perhaps unusual, if not unhealthful development of the religious sentiment here, was the fact that a large portion of the population are women whose husbands and sons are either abroad on the sea, or else drowned, and there is nobody but they and the ministers left behind.”
—Henry David Thoreau (18171862)
“No throne exists that has a right to exist, and no symbol of it, flying from any flagstaff, is righteously entitled to wear any device but the skull and crossbones of that kindred industry which differs from royalty only businesswise-merely as retail differs from wholesale.”
—Mark Twain [Samuel Langhorne Clemens] (18351910)