The skull.pdf

The Skull DR.FAHD AL-AMODI LECT.2 OMS(HSC),BDS 24/09/2023 The skull : The skull is the skeleton of the head. * Structure: it is formed of 22 bones: - One movable bone: the mandible which articulates by synovial joint. - 21 immovable bones articulating t...

The Skull DR.FAHD AL-AMODI LECT.2 OMS(HSC),BDS 24/09/2023 The skull : The skull is the skeleton of the head. * Structure: it is formed of 22 bones: - One movable bone: the mandible which articulates by synovial joint. - 21 immovable bones articulating together by fibrous joints. The 21 immovable bones include: Parts of the Skull: (1) Cranium: the upper & post. part which encloses the brain. (2) Facial Skeleton: is the ant. part of the skull which includes: (a) an upper fixed part. (b) lower movable part (the mandible). Different aspects of the Skull: (1) anterior aspect or Norma Frontalis. (2) superior aspect or Norma Verticalis. (3) lateral aspect or Norma Lateralis. (4) posterior aspect or Norma Occipitalis. (5) inferior aspect or Norma Basalis. (6) the interior of the skull or Cranial Cavity is studied by removal of the skull cap. I- THE NORMA VERTICALIS * It is the upper aspect (Vault) of the skull. * Bones forming it: 4 bones: (1) Frontal bone ------anteriorly. (2) 2 Parietal bones ----on each side. (3) occipital bone ------posteriorly. Sutures between the bones: (1) the Coronal Suture: runs transversely between the frontal bone & the 2 parietal bones. (2) the Sagittal Suture: runs in the median plane, connecting the 2 parietal bones. (3) the Lambdoid Suture: runs between the occipital bone & the 2 parietal bones. Special Features: (1) The Bregma: it is the point of meeting between the sagittal & coronal sutures. - At birth, this area is occupied by a rhomboidal-shaped membrane called the Anterior Fontanelle which ossifies at the age of 18 months. (2) Vertex: it is the middle of the sagittal suture. -It is the highest point of the skull. (3) The Lambda: it is the point of meeting between the sagittal & lambdoid sutures.  Anterior At birth, it is occupied by a fontanella small Δ membrane called Post. Fontanelle which ossifies at the age of 6 months. Posterior fontanella (4) 2 Frontal eminences: the most convex parts of the frontal bone. - They indicate the site of the ossification centres of frontal bone. (5) 2 Parietal eminences: the most convex parts of the parietal bones. - They indicate the site of the ossification centres of parietal bones. (6) Parietal emissary foramen: - one on each side of the sagittal suture, about 3-5 cm infront of the lambdoid suture. - it transmits an emissary vein connecting the scalp veins with the sup. sagittal sinus. II- THE NORMA 0CCIPITALIS Bones forming norma occipitallis - 2 parietal borders ---------- on the sides & above. - 2 mastoid temporal bones ----- on the sides & below. - squamous part of occipital bone --------below & behind. Sutures between the bones: (1) Lambdoid suture: between the 2 parietal bones & the occipital bone. (2) Occipito-mastoid suture: between the occipital & the mastoid temporal bones. Special features: (1) external occipital protuberance: - lies midway between the lambda & the foramen magnum. - its centre is called the inion. - its upper part gives origin to trapezius muscle. - its lower part gives attachment to the upper part of the nuchal lig. (2) External occipital crest: - it extends from the external occipital protuberance to the post. border of the foramen magnum. -it gives attachment to the base of the nuchal lig. (3) Superior nuchal line: - it is a bony ridge extending from the external occipital protuberance towards the mastoid process. - its medial 1/3 gives origin to the trapezius m. - its lateral 1/3 gives insertion to the sternomastoid m. (4) Inferior nuchal line: - another bony ridge extending laterally from the middle of the external occipital crest, parallel to the sup. nuchal line & below it. (5) Highest nuchal line: - it is a faint ridge lying 1 cm above the sup. nuchal line. - its medial part gives attachment of the epicranial aponeurosis. - its lateral part gives origin of occipital belly of occipitofrontalis m. (6) Mastoid emissary foramen: - it lies on the back of the mastoid process close to the occipitomastoid suture. - it gives passage to an emissary vein (between the sigmoid sinus & the occipital veins).