Skull Anatomy PDF

Skull Anatomy Introduction Assistant professor Dr Ali Alnajjar General Surgeon  The Skull The skull, the body’s most complex bony structure, is formed by the cranium and facial bones Cranium – protects the brain and is the site of attachment for head and neck musc...

Skull Anatomy Introduction Assistant professor Dr Ali Alnajjar General Surgeon  The Skull The skull, the body’s most complex bony structure, is formed by the cranium and facial bones Cranium – protects the brain and is the site of attachment for head and neck muscles Facial bones – Supply the framework of the face, the sense organs, and the teeth – Provide openings for the passage of air and food – Anchor the facial muscles of expression  The Skull The skull is composed of 22 bones, which may be divided into the cranium and facial bones cranium 8 bones contains and protects the brain one frontal bone one ethmoid bone one sphenoid bone one occipital bone two temporal bone two parietal bone facial bones 14 bones that surrounded the eye, nose and mouth two maxilla two nasal bone , two lacrimal bone , two palatine bone, two zygomatic bone , two inferior nasal concha one mandible, one vomer  parietal bone Frontal bone Sphenoid bone Temporal bone Zygomatic bone Occipital bone Nasal bone Maxilla Mandible  Frontal Bone Forms the anterior portion of the cranium Articulates posteriorly with the parietal bones via the coronal suture Major markings include the supraorbital margins, the anterior cranial fossa, and the frontal sinuses (internal and lateral to the glabella) Skull: Anterior View Figure 7.2a Frontal bone anterior view Frontal bone inferior view  Parietal Bones and Major Associated Sutures Four sutures mark the articulations of the parietal bones – Coronal suture – articulation between parietal bones and frontal bone anteriorly – Sagittal suture – where right and left parietal bones meet superiorly – Lambdoid suture – where parietal bones meet the occipital bone posteriorly – Squamosal or squamous suture – where parietal and temporal bones meet  Parietal Bones and Major Associated Sutures Form most of the superior and lateral aspects of the skull Figure 7.3a  Occipital Bone and Its Major Markings Forms most of skull’s posterior wall and base Major markings include the posterior cranial fossa, foramen magnum, occipital condyles, and the hypoglossal canal Figure 7.2b Occipital Bone and Its Major Markings Figure 7.4b  Temporal Bones Form the inferolateral aspects of the skull and parts of the cranial floor Divided into four major regions – squamous, tympanic, mastoid, and petrous Major markings include the zygomatic, styloid, and mastoid processes, and the mandibular and middle cranial fossae Major openings include the stylomastoid and jugular foramina, the external and internal auditory meatuses, and the carotid canal Temporal Bones Figure 7.5  Sphenoid Bone Butterfly-shaped bone that spans the width of the middle cranial fossa Forms the central wedge that articulates with all other cranial bones Consists of a central body, greater wings, lesser wings, and pterygoid processes Major markings: the sella turcica, hypophyseal fossa, and the pterygoid processes Major openings include the foramina rotundum, ovale, and spinosum; the optic canals; and the superior orbital fissure Sphenoid Bone Figure 7.6a, b  Ethmoid Bone Most deep of the skull bones; lies between the sphenoid and nasal bones Forms most of the bony area between the nasal cavity and the orbits Major markings include the cribriform plate, crista galli, perpendicular plate, nasal conchae, and the ethmoid sinuses Ethmoid Bone Figure 7.7  VAULT The vault is made up by frontal, 2 parietals, occipital, greater wings of sphenoid, temporal bones. The coronal suture is located between the frontal bone & 2 parietal bones. The sagittal suture is between 2 parietal bones.. The lambdoid suture is between 2 parietals &occipital. In frontal bone smooth elevation over medial part of orbit which is called superciliary arch which form eye brow ridge. Supra orbital notch (or foramen) found at the junction of the medial 1/3 and lateral 2/3 of supra orbital margin. The frontal bone contains 2 frontal Para nasal air sinuses, then frontal bone projects posteriorly forming orbital part of bone (roof of the orbit) Vault superior view Vault inferior view Fontanels Figure 7.21a Fontanels Figure 7.21b  2 parietal bones form greater part of vault superiorly and laterally, the lateral wall of the vault is completed by greater wing of sphenoid and squamous part of temporal bone. H shaped irregular suture (pterion) is the junction between greater wing of sphenoid, squamous temporal, frontal and parietal bones. Pterion is crossed internally by the anterior branch of middle minengeal artery and vein. the lateral wall of vault ends inferiorly by infratemporal crest. Intracranial dural venous sinuses are connected to extra cranial veins by many emissary veins through number of small foramina in vault.  Muscle marking on vault On lateral surface of vault superior and inferior temporal lines which begins anteriorly as single line from ridge of frontal bone and diverge posteriorly ,the superior fade out while inferior temporal line curve down and anteriorly to reach the root of the zygomatic arch. The temporal fossa is bounded superiorly by superior temporal line. External occipital protuberance is the end of external occipital crest which begins at the posterior margin of foramen magnum. The superior nucheal line starts from protuberance and just below it is the inferior nucheal line  Internal surface of vault Sagittal sulcus is a groove produced by the superior sagittal sinus it begins on the inner surface of the frontal bone and runs posteriorly to ends in internal occipital protuberance. Inner surface of each parietal bone lateral to sagittal sulcus is marked by irregular groove produced by branches of middle minengeal blood vessels  CRANIAL BASE The superior endocrinal surface of cranial base is subdivided into:- anterior cranial fossa middle cranial fossa posterior cranial fossa. Cranial fossae  Anterior cranial fossa The anterior cranial fossa forms the anterior 1/3 of cranial base ,frontal lobe of brain is located here, the floor of anterior cranial fossa is formed by orbital part of frontal bone and lesser wings of the sphenoid bone these 2 bones form the roof of orbital cavity. medially each wing bears anterior clinoid processes. Orbital parts of frontal bone are separated from each other by cribriform plate of ethmoid bone. behind cribriform plate is the body of sphenoid with joint called sphenoethmoidal joint.  Continue anterior cranial fossa The posterior boundary of the fossa is by the anterior border of optic groove. In the middle of cribriform plate there is an up ward projection called Crista galli. The crista galli gives an attachment to the anterior edge of the Falex cerebri. In front of crista galli there is foramen caecum (usually a blind ended canal) but occasionally transmitting vessels connecting veins of nose with superior sagittal sinus on each side of galli a narrow nasal slit. Anterior and posterior ethmoidal canals are openings between the cribriform plate and orbital part of frontal bone transmitting ethmoidal nerves and vessels  MIDDLE CRANIAL FOSSA The middle cranial fossa is bounded in front by posterior border of lesser wings of sphenoid and anterior margin of optic groove. The fossa is bounded in behind by the posterior borders of petrous parts of the temporal bones with the dorsum sellae in between. Dorsum sellae is a prominent projection on the endocranial surface of body of sphenoid. The central region of fossa is short anteroposteriorly and is formed by body of sphenoid , while lateral regions are wide and formed by greater wings of sphenoid and petrous, squamous parts of temporal bone. The temporal lobes of brain located on both sides of middle cranial fossa.  Continue middle cranial fossa In the body of sphenoid there is pituitary fossa in which the pituitary gland is located in front of this fossa the optic groove with 2 optic canals on sides which transmit optic nerves and ophthalmic arteries to the orbit. Posterior to pituitary fossa is the dorsum sellae and the super lateral angles of dorsum sellae are called posterior clinoid processes. This area of sphenoid is called sella turcica. Between the greater wings and the lesser wings of the sphenoid there is the superior orbital fissure through which middle cranial fossa communicates with the orbital cavity. The superior orbital fissure transmit the 3rd, 4th, 6th, cranial nerves, ophthalmic branch of trigeminal nerve, superior and inferior ophthalmic veins.  Continue middle cranial fossa The medial part of each greater wing is pierced by 3 foramina. 1-foramen rotundum runs into pterygopalatine fossa and transmits maxillary division of trigeminal nerve. 2-foramen ovale which opens into infratemporal fossa and transmits: - a-mandibular division of trigeminal nerve. b-lesser petrosal nerve. c-accessory meningeal artery. d-recurrent meningeal branch of trigeminal nerve (nervous spinosus). e-emissary vein.  Continue middle cranial fossa 3-foramen spinosum transmits:- a-middle meningeal vessels b-nervous spinosus (meningeal branch of mandibular division of trigeminal nerve). 4-foramen lacerum which is medial to ovale with irregular edge bounded by petrous temporal bone and body and greater wing of sphenoid. 5- carotid canal which is a large sinus channel traversing the petrous bone and transmitting internal carotid artery and located at posterior wall of lacerum. 6-pterygoid canal located at anterior wall of lacerum which transmits nerve of pterygoid canal.  Continue middle cranial fossa Behind lacerum petrous temporal is marked by shallow concavity (trigeminal impression) which lodges the trigeminal ganglion. Lateral to trigeminal impression there is hiatus and groove to transmit greater petrosal nerve a branch of facial nerve.  POSTERIOR CRANIAL FOSSA Is the largest and deepest of 3 cranial fossae, cerebellum and brain stem located here. Its floor is formed by body of sphenoid posterior to dorsum sellae and basilar part of occipital bone. The lateral part of floor is formed by squamous part of occipital bone. foramen magnum in the middle of fossa traversed by medulla oblongata with meninges, spinal roots of accessory nerve and vertebral arteries. Jugular foramen located at posterolateral end of petro- occipital fissure, it transmits 9th, 10th, 11th, nerves and the sigmoid, inferior petrosal venous sinuses.  Posterior cranial fossa The internal acoustic meatus is opened on posterior surface of petrous bone, and transmits the vestibule- cochlear nerve and the motor and sensory roots of the facial nerve. Hypoglossal canal has the internal opening in the anterolateral wall of foramen magnum, while the external opening is lateral to occipital condyle, hypoglossal canal transmits hypoglossal nerve and meningeal branch of the ascending pharyngeal artery. Behind foramen magnum there is internal occipital crest which ends above as internal occipital protuberance and gives attachment to falex cerebelli. There is a shallow groove marking the place of transverse venous sinuses.  INFERIOR SURFACE OF CRANIAL BASE INFERIOR SURFACE OF MIDDLE CRANIAL FOSSA *The inferior surface of the middle cranial fossa is very irregular. The pterygoid processes projecting from the junction of greater wing and body of sphenoid, pterygoid processes articulate with perpendicular plate of palatine bone. Lateral pterygoid plate gives origin laterally to lateral pterygoid muscle and medially to medial pterygoid muscle. Inferior view of skull  Continue inferior surface of middle cranial fossa The medial pterygoid plate gives attachment to the superior constrictor muscle. The lower end of the medial pterygoid plate forms the hamulus which gives attachment to pterygomandibular raphe and to fibers of superior constrictor muscle. Between the left and right pterygoid plates the posterior nasal aperture divided into two by median vomer bone, the nasopharynx is located immediately behind the posterior nasal aperture. The body of sphenoid forms roof of nasopharynx and posterior part of nasal cavity.  The infratemporal fossa The infratemporal fossa lies lateral to pterygoid process, (greater wing+squamous temporal bones form the floor of infratemporal fossa). The infratemporal fossa contains the following structures:- 1-pterygoid muscles. 2-mandibular division of trigeminal nerve. 3-maxillary artery. 4-pterygoid plexus of veins.  The infratemporal fossa is bounded by :- - anteriorly:-posterior surface of maxilla - superiorly:-inferior surface of greater wing of sphenoid. -medially:-lateral pterygoid plate. -laterally:-ramus of the mandible. -infratemporal fossa has no bony floor or posterior wall, and posteriorly the carotid sheath located.  The infratemporal fossa communication The infratemporal fossa communicates with the temporal fossa through the gap between the zygomatic arch and the side wall of the cranial base (brain case). The openings into the infratemporal fossa are:- 1-foramen ovale. 2-foramen spinosum. 3-pterygomaxillary fissure. 4-inferior orbital fissure.  The inferior orbital fissure is located between the upper margin of the posterior wall of the maxilla and the greater wing of the sphenoid. The inferior orbital fissure connects:- 1-the orbit with infratemporal fossa laterally. 2-the orbit with pterygopalatine fossa medially.  The inferior orbital fissure transmits:- 1-the maxillary nerve (which becomes infraorbital nerve once it has entered the orbit) 2-zygomatic nerve (which becomes zygomaticofacial and zygomaticotemporal nerves) 3-infraorbital vessels. 4-connects inferior ophthalmic vein and the pterygoid plexus of veins.  Between foramen spinosum and inferior opening of carotid canal there is groove for cartilaginous part of auditory tube (Eustachian tube). The inferior surface of the petrous bone is very irregular and is separated from body of sphenoid by foramen lacerum. Posterolateral to lacerum there is the opening of the carotid canal. behind the carotid canal there is deep depression termed jugular fossa. Articular tubercle for articulation of lower jaw (temporomandibular joint) found on inferior surface of squamous temporal bone, behind this tubercle there is mandibular fossa.  INFERIOR SURFACE OF POSTERIOR CRANIAL FOSSA Foramen magnum is a wide opening, on either side of foramen there is occipital condyles by which skull articulates with 1st cervical vertebra (atlas) at the synovial atlanto-occipital joints. Hypoglossal canal opens lateral to the condyle, laterally there is jugular foramen. Posterolateral to jugular foramen there is mastoid process of temporal bone which gives insertion to the sternocliedomastoid muscle, medial to mastoid process is mastoid notch which gives origin to posterior belly of digastric muscle. Stylomastoid foramen between mastoid and styloid process, which transmits facial nerve. Continue inferior surface of posterior cranial fossa Anterior to foramen magnum the pharyngeal tubercle present which gives attachment to upper most fibers of the superior constrictor muscle.  FACIAL SKELETON ORBIT The orbital cavities are pyramidal recesses containing the eye balls with their muscles, vessels and nerves also lacrimal apparatus. Each orbit has base (orbital opening) apex, roof, floor, medial and lateral walls. Roof: - 1-orbital part of frontal bone. 2-lesser wing of the sphenoid. Lateral wall:- 1-orbital surface of zygomatic bone. 2-greater wing of sphenoid.  Continue boundaries of orbit Floor:-1-body of maxilla (upper surface). 2-orbital plate of palatine bone at posteromedial corner of floor. Medial wall:- 1-frontal process of maxilla. 2-lacrimal bone. 3-orbital plate of ethmoidal labyrinth. 4-body of sphenoid.  Orbit The lateral wall and the roof are separated posteriorly by the superior orbital fissure (lying between the greater and lesser wings of sphenoid) The superior orbital fissure transmits the nerves to the muscles moving the eye ball, ophthalmic division of trigeminal nerve and ophthalmic veins. The lateral wall and floor are separated by inferior orbital fissure (between maxilla and greater wing of sphenoid) in its posteromedial part the fissure communicates with pterygopalatine fossa while its anterolateral part communicates with infratemporal fossa.  Orbit Infraorbital groove arise from medial part of inferior orbital fissure, this groove is changed to a canal and opened on front of maxilla as infraorbital foramen which transmits infraorbital nerve (a continuation of maxillary nerve). Optic canal near medial end of superior orbital fissure and lying between the roots of the lesser wing of sphenoid. Optic canal transmits optic nerve and ophthalmic artery. Lacrimal groove located on anterior aspect of medial wall for lacrimal sac, the nasolacrimal canal descend down from groove which opened into inferior meatus of nasal cavity.  NASAL CAVITY The nasal cavity is an irregular cavity lying between bony palate below and the floor of anterior cranial fossa above. Superiorly the nasal cavity is located between the orbital cavities while inferiorly between maxillae. The nasal cavity is divided by nasal septum which is composed of bony and cartilaginous parts.  Boundaries of nasal cavity The roof of nasal cavity is formed by:- 1-nasal bones. 2-cribriform plate of ethmoid. 3-body of sphenoid. The floor of nasal cavity is formed by:- 1-palatine process of maxilla. 2-horizontal plates of palatine bones.  Continue nasal cavity Anteriorly each maxillary palatine process is pierced close to septum by incisive canal which transmits nasopalatine nerve (branch from pterygopalatine ganglion) and terminal branch of the greater palatine artery, the canals of the 2 sides opened inferiorly into incisive foramen.  The lateral wall of nasal cavity is very irregular and formed by:- 1-maxilla. 2-labyrinth of ethmoid. 3-nasal, lacrimal, palatine bones and the inferior nasal concha. Posterior to lacrimal bone the superior part of lateral nasal wall is provided by medial plate of ethmoid labyrinth projecting into nasal cavity. From the medial plate 2 curved laminae superior and middle nasal conchae.  Palatine bone The Palatine bone consist of horizontal and perpendicular plates, the horizontal plate forms posterior part of hard palate while perpendicular plate articulate with the body of the sphenoid, here the perpendicular plate intervenes between the nasal cavity and the pterygopalatine fossa and is pierced by the Sphenopalatine foramen through which nasal branches of the pterygopalatine ganglion and maxillary artery pass from pterygopalatine fossa into the nose.  Palatine bone medially anteriorly  Conchae & meatuses The inferior nasal concha is a separate bone located below middle concha articulates with lateral wall of nasal cavity. The conchae incompletely divided the nasal cavity into 3 passages or meatuses. -superior meatus is between superior and middle conchae. -middle meatus is between middle and inferior meatus. -inferior meatus between inferior concha and palate. Each meatus is communicating anteriorly, posteriorly and medially with the remainder of the nasal cavity.  The area of the lateral wall above the superior concha is termed the sphenoethmoidal recess. The structures opening into the lateral wall of the nose are: 1-sphenoidal air sinus into sphenoethmoidal recess. 2-posterior ethmoidal air cells into superior meatus. 3-the frontal and maxillary sinuses, anterior and middle ethmoidal air cells into the middle meatus. 4-the nasolacrimal canal into the inferior meatus  *Immediately posterior to superior meatus is the sphenopalatine foramen (through which the nasal branches of pterygopalatine ganglion and maxillary artery pass). *The septum of the nose is bony and cartilaginous parts, the bony nasal septum extends from the roof of the nasal cavity to its floor, it is thin sheet of bone formed by the vomer and the perpendicular plate of the ethmoid  THE UPPER JAW AND BONY PALAT The upper jaw is made up of 2 maxillae, each maxilla contains body and four processes :- 1-zygomatic process to form anterior part of zygomatic arch. 2-frontal process projected medially to form medial wall of orbit. 3-palatine process which project medially to form bony palate. 4-alveolar process which projects down wards and contain alveoli for roots of upper teeth.  body of maxilla The body of maxilla is large and contains maxillary para nasal sinuses, the upper (orbital) surface of the body occupies the floor of the orbit The anterior surface form the curved external surface of the upper jaw The medial (nasal) surface forms lateral wall of nasal cavity.  Continue body of maxilla Above the incisor teeth the anterior surface has shallow depression termed incisive fossa lateral to it canine fossa, above them is infra orbital foramen. The posterior (infra temporal) surface provides the anterior wall of the infra temporal fossa. Below the anterior nasal aperture there is median projection called anterior nasal spine. Maxillary tuberosity :- is a rounded eminence located behind the last molar tooth, above this tuberosity on the posterior maxillary surface there is posterior alveolar canal. Maxilla lateral view  Hard palate Hard palate :- is the bony palate with its mucous membrane, the bony palate is formed :- 1- anteriorly by palatine process of maxillae 2- posterior 1/4 by horizontal plates of the palatine bones. Median suture between the right and left sides of hard palate. Transverse suture between palatine processes of maxillae and horizontal plates of palatine bones. Incisive fossa seen in midline shortly behind central incisors which receives 2 incisive canals.  Continue hard palate Medial to last molar there is greater and lesser palatine foramina, these are the inferior openings of the greater palatine canal which runs down from the pterygopalatine fossa, these foramina transmit nerves and vessels of the same name. From the greater palatine foramen there is a groove which contain greater palatine neurovascular bundle in its course in palate. The posterior border of the hard palate has a median projection termed posterior nasal spine. Palate  THE ZYGOMATIC ARCH The arch is formed by: - (from anterior to posterior) 1-zygomatic process of maxilla. 2-zygomatic bone. 3-zygomatic process of the squamous part of temporal bone. Temporal fascia attached to the upper border of zygomatic arch. Masseter muscle arises from inferior and medial borders of zygomatic arch.  Mandible The mandible consists of a curved body (Horse-Shoe ) and 2 vertical rami ,Symphysis menti is site of union after birth Body:- The body has external (buccal or labial ) and internal (lingual) surfaces anteriorly there is mental protuberance Oblique line runs backward and upward until below last molar tooth , above this line there is mental foramen which transmits mental branches of the inferior alveolar nerve and blood vessels which themselves run in the mandibular canal within the body of the mandible.  Internal surface of the body bears on oblique ridge , the mylohyoid line which begins below last molar and runs downwards and forwards below this line is sub-mandibular fossa [sub- mandibular salivary gland lodge here]. Mylohyoid groove runs from ramus down to sub- mandibular fossa in which mylohyoid branches of the inferior alveolar nerve and vessels run immediately above the line in region below the premolar teeth is the shallow sublingual fossa for sublingual salivary gland. Below incisor teeth there is superior and inferior mental spines for attachment of genial muscles , the upper part of the body of the mandible isTormed by the alveolar process which contains sockets for roots of the lower teeth  Ramus of the mandible is a quadrilateral palate of bone , in it’s center mandibular foramen which transmits the inferior alveolar nerve and blood vessels. this opening leads into the mandibular canal which runs downwards and forwards into the body of the mandible, lingula present over the foramen, postero inferior to mylohyoid groove is the insertion of the medial pterygoid muscle , the region where the inferior and posterior borders of the ramus meet is termed the angle of the mandible. The superior border of ramus forms coronoid process anteriorly and condylar process posteriorly and mandibular incisure between them. From medial aspect of coronoid to last molar there is temporal crest, between this crest and anterior boarder of ramus is retro molar fossa The condylar process forms head of mandible , which articulates with squamous part of temporal bone at temporomandibular joint