Anatomy Winter

• The skull


  • Frontal bone
  • Parietal bone
  • Occipital bone

  
• The skull


  • It is the bony skeleton of the head and most complex osseous structure in the body
  • It is a modified part of the axial skeleton together with vertebral column, ribs and sternum
  • It is composed of 28 separate bones, of which most are paired, but some in the median plane are single
  • The majority of bones in the skull are held by fibrous joints termed sutures
  • It can be subdivided into cranium and mandible, based upon the fact that most of bones of the skull articulate by fixed joints, mandible is easily detached
  • It can be divided into neurocranium and viscerocranium

  
• Neurocranium


  • It protects the brain and organs of special sense
  • It is divided into the upper part termed the calvaria or calva (skull "cap") and inferior part basis cranii or the base of the cranium

  
• The cranial cavity contains the brain, pineal and hypophyseal (pituitary) gland, parts of cranial nerves, blood vessels, meninges and cerebrospinal fluid

  
• The important nerves and vessels pass in and out of the skull via openings termed foramina

  
• Cranial bones


  • They consist of two thin plates of compact bones: outer and inner tables, separated by diploe
  • Trabecular bones contain red bone marrow

  
• Frontal bone


  • It is like half a shallow, irregular cap forming the forehead or frons
  • It is a pneumatic bone (frontal sinus)
• Frontal bone


  • It has two parts: vertical and horizontal part
  • Each part has external and internal surface

  
• Parts of the frontal bone

  • Vertical - squamous part
  • Horizontal part
• Vertical - squamous part of the frontal bone

  • It forms the major portion of the bone
  • The external surface has rounded frontal tuber, superciliary arches, supra-orbital margins, zygomatic process, temporal line, nasal part
  • The internal surface is concave, has a vertical groove for the superior sagittal sinus, frontal crest, impressions for cerebral gyri and furrows for meningeal vessels

  
• Horizontal part of the frontal bone

  • The external surface is divided into two orbital and one nasal part
  • The orbital parts are two thin, triangular laminae separated by wide ethmoidal notch
  • The nasal part has the serrated nasal notch, nasal spine, ethmoidal notch

  
• Frontal sinus


  It is a paired structure which consists of two irregular cavities placed behind the superciliary arches, each communicating with the middle meatus of the nasal cavity
• Occipital bone


  • It forms the back and base of the cranium
  • It has four parts which enclose the foramen magnum: squama, basilar part, lateral parts

  
• Squama of the occipital bone

  • It is convex externally and concave internally
  • The external surface presents the external occipital protuberance, nuchal lines, external occipital crest
  • The internal surface is divided into four deep fossae by an internal occipital protuberance and by sagittal and horizontal extensions from it

  
• Basilar part of the occipital bone


  • It extends anteriorly from the foramen magnum, fusing with the sphenoid in adults
  • The inferior surface has a small pharyngeal tubercle, the superior surface forms part of the clivus

  
• Lateral (condylar) parts of the occipital bone


  • They flank the foramen magnum
  • The inferior surface has occipital condyles for articulation with the atlas
  • The superior surface has a jugular tuberculum, jugular process, groove for the sigmoid sinus

  
• Parietal bone


  • It forms the most of the cranial roof and sides
  • It has two surfaces, four borders and four angles

  
• Surfaces of the parietal bone

  • External surface
  • Internal surface

  
• Borders of the parietal bone

  • Sagittal border
  • Squamous (inferior) border
  • Frontal border
  • Occipital border

  
• Angles of the parietal bone

  • Frontal (antero-superior) angle
  • Spenoidal (antero-inferior) angle
  • Occipital (postero-superior) angle
  • Mastoid (postero-inferior) angle

  
• Ethmoid bone


  • It lies in the anterior part of the cranial base and participates in formation of the medial wall of the orbits, as well as the roof, lateral and medial wall of the nasal cavity
  • It has a horizontal, perforated cribriform plate, a median perpendicular plate and two lateral labyrinths which contain ethmoidal air cells

  
• Cribriform plate of the ethmoid bone

  • It fills the ethmoidal notch of the frontal bone and forms a large part of the roof of the nasal cavity
  • It is penetrated by numerous foramina
  • A triangular median crista galli projects up from this lamina

  
• Perpendicular plate of the ethmoid bone

  • It descends from the cribriform plate to form the upper part of the nasal septum

  
• Ethmoidal labyrinths


  • They consist of thin-walled ethmoidal air cells, classified in the anterior, middle and posterior group
  • The lateral surface or orbital plate is part of the medial orbital wall
  • The medial surface forms part of the lateral nasal wall and ends as the convoluted middle nasal concha and superior nasal concha
• The ethmoidal cells (sinuses) are present at birth and recognizable through the use of CT scanning by two years of age
• Sphenoid bone


  • It lies in the base of the skull, among the frontal, temporal and occipital bone
  • It has body, paired greater and lesser wings and two pterygoid processes, descending from junctions of the body and greater wings
  • The body contains sphenoidal sinuses

  
• Body of the sphenoid bone

  • It is cuboidal in shape and contains two paranasal sphenoidal sinuses
  • The cerebral or superior surface has the jugum sphenoidale, prechiasmatic sulcus, Turkish saddle (sella turcica), clivus
  • The lateral surfaces have carotid sulcuses
  • The anterior surface has the sphenoidal crest

  
• Bodyof Sphenoid

  Cuboidal in shape (it has six surfaces) and it contains two paranasal sphenoidal sinuses
• Cerebral or superior surface of the body

  • Anteriorly, the jugum sphenoidale is placed
  • Posterior to it lies the Turkish saddle (sella turcica), which consists of: tuberculum sellae, hypophysial fossa (containing the pituitary gland) and dorsum sellae
  • The tuberulum sellae is completed laterally by two middle clinoid processes and dorsum sellae by two posterior clinoid processes

  
• Posterior surface of the body

  • The sphenoidal body, together with the basilar part of the occipital bone, forms the clivus

  
• Lateral surfaces of the body

  • Have carotid sulcuses, which accommodate the internal carotid artery and cavernous sinus

  
• Anterior surface of the body

  • Has the sphenoidal crest, which joints the ethmoid bone
  • On each side of the crest is an opening of the sphenoidal sinus
  • The sphenoidal sinuses are closed antero-inferiorly by sphenoidal conchae

  
• Inferior surface of the body

  • Bears a median triangular sphenoidal rostrum, which articulates with the vomer
  • On each side of the posterior part of the rostrum a thin vaginal process is placed

  
• Lesser wings


  • Triangular in shape, protruding laterally from the superior margin of the body
  • Connected to the body by anterior and posterior root
  • Between roots lies the optic canal, containing the optic nerve and ophthalmic artery
  • The suprior surface of each wing is a smooth
  • The inferior surface, together with the greater wing, forms the superior orbital fissure
  • On the medial end of the posterior border of the lesser wings anterior clinoid processes are located
• Superior orbital fissure


  • Triangular in shape, connects middle cranial with orbital cavity
  • Bounded medially by sphenoidal body, superiorly by the inferior surface of the lesser wing and inferiorly by the orbital surface of the greater wing

  
• Greater wings


  • Connected to the body by three roots
  • Between anterior and middle root is foramen rotundum (transmitting the maxillary nerve)
  • Between middle and posterior root is foramen ovale (transmitting the mandibular nerve)
  • On the spine of the sphenoid bone is foramen spinosum (transmitting the middle meningeal artery and meningeal branch of the mandibular nerve)
  • Cerebral surface participates in formation of the middle cranial fossa
  • Lateral surface is divided into temporal surface, infratemporal surface, orbital surface and maxillary surface

  
• Pterygoid processes


  • Descend perpendicularly from the junctions of greater wings and body
  • Each consists of a medial and lateral plate, which upper parts are fused anteriorly
  • Below, the plates are separated by pterygoid notch and posteriorly they diverge in the pterygoid fossa
  • Above is the small, oval scaphoid fossa (for the tensor veli palatini muscle attachment)
  • The anterior surface of the root of the pterygoid process is pierced by the anterior orifice of the pterygoid canal
  • The lateral pterygoid plate is thin
  • The medial pterygoid plate is narrower and longer, its lower end curves into pterygoid hamulus
  • The medial plate is prolonged above on the sphenoid body's inferior aspect as the thin vaginal process

  
• Sphenoidal sinus


  Undeveloped at birth, pneumatization begins at the age of three and progress posteriorly
• Temporal bones are placed in the sides of the calvaria and the base of the skull

  
• Squamous part of the temporal bone

  • Thin, has vertical and horizontal part
  • Vertical part has convex external surface forming part of the temporal fossa, and concave internal surface showing grooves for the branches of middle meningeal vessels
  • Horizontal part consists of the zygomatic process and mandibular fossa