Question

Whit is Membranous Neurocranium

Answer 1

The flat bones that form sides and roof of the skull (frontal bones, pa­rietal bones, squamous parts of the temporal bones and interparietal part of the occipital bone) develop by the intra-membranous method of osteogenesis in the mesenchyme that invests the developing brain. This mesenchyme is derived from two sources: (1) neural trest cells, and (2) paraxial rriesoderm of the head region.
At birth the bones of the mem­branous neurocranium are separated from each other by narrow seams of connective tissue called sutures. In the areas where more than two bones meet, the sutures are wide and consti­tute fontanelles. During parturition (ie, birth process) the soft, fibrous sutures that join the flat bones of the skull vault allow the skull to deform as it passes through the birth canal. In the skull of a newborn six fontanelles are present which occupy the regions between the corners of the bones of the skull vault. The two most important fontanelles are the anterior fontanelle (present be­tween frontal and parietal bones), and the posterior fontanelle (located be­tween the parietal and occipital bones). As the process of ossi-fication contin­ues postnatally, the posterior fontanelle closes by three.months after birth, but the anterior fontanelle persists for a much longer period and closes at about 2 years of age. Though the fontanelles close in the early childhood, the su­tures between the bones of the skull vault persist into the adulthood. How­ever, with the advancing age, the bones of the membranous neurocra­nium gradually fuse with each other (ie, synostosis occurs) and finally the su­tures become completely closed in the old age.
The anterior fontanelle is of great clinical importance. It pulsates because of the underlying cerebral ar­teries and is easily palpable in an in­fant. Palpation of this fontanelle is used to estimate the intracranial pressure and assess the degree of ossification of the skull. A sample of blood may be obtained from the underlying superior sagittal sinus by inserting a needle through the anterior fontanelle.