Human Skull Anatomy: Norma Basalis Externa & Interna (PDF)

Skull II Norma Basalis Externa & Norma Basalis Interna By: Islam Omar Seiam Assistant Professor of Human Anatomy & Embryology, Faculty of Medicine, Suez Canal University  Definition: It is the outer surface of the base of the skull.  Parts: -Norma basalis externa is divided into 3 pa...

Skull II Norma Basalis Externa & Norma Basalis Interna By: Islam Omar Seiam Assistant Professor of Human Anatomy & Embryology, Faculty of Medicine, Suez Canal University  Definition: It is the outer surface of the base of the skull.  Parts: -Norma basalis externa is divided into 3 parts: 1. Anterior part 2. Middle part 3. Posterior part -These 3 parts are divided by 2 imaginary transverse line: 1. Line (1): Passing along the posterior border of hard palate. 2. Line (2): Passing along posterior border of foramen magnum.  Anterior part Hard palate Line (1) Middle part Foramen magnum Line (2) Posterior part (1) Anterior part Forming bones: -It is formed of hard palate that is divided into right & left halves by median palatine suture. -Each half is divided into: 1. Anterior 2/3: Formed of palatine processes of maxilla. 2. Posterior 1/3: Formed of horizontal plate of palatine bone.  Palatine processes of Intermaxillary suture Hard maxilla palate Horizontal plate of Palatomaxillary palatine bone suture 2/3 Interpalatine 1/3 suture  Bony features: 1. Alveolar arch: Forms a U-shaped ridge of bone called alveolar arch, which bears the sockets for the roots of upper teeth. 2. Posterior nasal spine: Is a conical projection in the median plane on the sharp free posterior border of the hard palate. 3. Maxillary tuberosity: A projection from the posterior end of alveolar arch. 4. Pyramidal process of palatine bone: Projects posterolaterally from palatine bone behind the maxillary tuberosity.  Alveolar arch Maxillary tuberosity Pyramidal process of palatine bone Posterior nasal spine  Foramina: 1. Incisive fossa: A small pit anteriorly in the midline behind the incisor teeth. Has 4 foramina inside: (a) Two median foramina: To transmit right & left long sphenopalatine nerves. (b) Two lateral formina: To transmit right & left greater palatine nerves & vessels. 2. Greater palatine foramen: One on each side, lies medial to the last molar tooth. It transmits the greater palatine nerve and vessels. 3. Lesser palatine foramina (1–3 in number): One on each side, lies in the pyramidal process of palatine bone. It transmits the lesser palatine nerve and vessels.  2 lateral 2 median Incisive fossa Greater palatine foramen Lesser palatine foramina (1-3 formina) (2) Middle part Forming bones: 1. Anteriorly: Vomer & body of sphenoid bone. 2. Anterolaterally: Pterygoid process of sphenoid bone, infratemporal surface of greater wing of sphenoid & squamous part of temporal bone. 3. Posterolaterally: Petrous, tympanic & mastoid parts of temporal bone. 4. Posteriorly: Basilar & 2 lateral parts of occipital bone.  Anterior part Posterior part  Vomer Body of sphenoid Pterygoid process of sphenoid bone Squamous part of temporal bone Infratemporal surface of greater wing of sphenoid  Petrous part of temporal bone Tympanic part of temporal bone Mastoid part of temporal bone Basilar part of occipital bone Two lateral parts of occipital bone  Bony features: 1. Choanae (posterior nasal apertures): Separated from each other by the vomer. 2. Vomer: Is a flat unpaired bone that forms a major part of the bony nasal septum. 3. Pterygoid processes of sphenoid bone: Each one has lateral and medial pterygoid plates with pterygoid fossa inbetween. Each one extends inferiorly on each side of the sphenoid from the junction of the body and greater wings. N. B. The upper end of medial pterygoid plate divides into: Scaphoid fossa (laterally) and pterygoid tubercle (medially). While, lower end forms pterygoid hamulus. 4. Groove for the cartilaginous part of the pharyngotympanic (Eustachian) tube: Lies between greater wing of the sphenoid and petrous part of the temporal bone. 5. Squamous part of the temporal bone: a. Has mandibular fossa: A depression for the tempro-mandibular joint. b. Has articular eminence: An elevation in front the mandibular fossa. 6. Infratemporal surface of greater wing of sphenoid bone: a. Has sphenoidal spine: which is a process at the apex of the great wing of the sphenoid. b. Has 2 foramina: Foramen ovale and foramen spinosum. 7. Inferior orbital fissure: A long fissure between greater wing of sphenoid bone and maxilla. It leads to the orbital cavity. 8. Petrous part of temporal bone: It is a wedge shaped bone between greater wing of sphenoid bone and basilar part of occipital bone. It has: a. Foramen lacerum: Between apex of petrous part of temporal bone, pterygoid process of medial pterygoid plate and basilar part of occipital bone. b. Rough quadrate area: A quadrangular area behind apex of petrous part of temporal bone. c. Carotid canal: Behind the rough quadrate area. d. Jugular foramen: Posterolateral to carotid canal. 9. Mastoid part of temporal bone: a. Has styloid process: A pointed process lateral to jugular foramen. b. Has mastoid process: A nipple like process behind styloid process. Has mastoid notch (medial to it) and occipital groove (medial to mastoid notch). c. Has stylomastoid foramen: Between mastoid and styloid processes. 10. Tympanic part of temporal bone: Has a fissure called squamotympanic fissure between it and mandibular fossa. 11.Basilar part of occipital bone: Articulates anteriorly with body of sphenoid bone. Shows midline elevation called pharyngeal tubercle. 12.Two lateral parts of the occipital bone: Each one has an occipital condyle for articulation with the 1st cervical vertebra. Each occipital condyle has anterior condylar foramen (hypoglossal canal) above it, and condylar fossa (or foramen) behind it. 13.Foramen magnum: Large foramen between the 2 occipital condyles.  Choanae Inferior orbital (posterior nasal apertures) fissure Vomer Mandibular fossa Pterygoid process of sphenoid Groove for the cartilaginous Articular eminence part of Eustachian tube Squamotympanic fissure Sphenoidal spine Rough quadrate area of Pharyngeal petrous part of temporal tubercle Foramen spinosum bone Foramen ovale Styloid process Carotid Canal Anterior condylar Stylomastoid Mastoid process foramen foramen Occipital condyle Jugular foramen Posterior condylar foramen Foramen magnum  Lesser wing Lesser wing Greater wing Greater wing Body Lateral pterygoid plate Medial pterygoid plate Pterygoid process Parts of Sphenoid Bone  Pterygoid hamulus Medial pterygoid plate Pterygoid fossa Lateral Scaphoid fossa pterygoid (laterally) plate Pterygoid tubercle (medially) Pterygoid Processes of Sphenoid bone Mastoid process Styloid process Stylomastoid foramen Mastoid notch Occipital groove Mastoid Part of Temporal Bone  Foramina: 1. Foramen ovale: Transmits Mandibular nerve / Motor root of trigeminal nerve / Middle meningeal vein / Accessory meningeal artery / Lesser superficial petrosal nerve / Emissary veins. 2. Foramen spinosum: Transmits Middle meningeal artery / Nervous spinosum. 3. Stylomastoid foramen: Transmits Facial nerve / Stylomastoid artery. 4. Foramen lacerum: Its lower end is closed by fibrocartilage, while its upper part transmits Internal carotid artery and greater petrosal nerve. Structure of Foramen Lacerum 5. Carotid canal: Transmits Internal carotid artery / Deep petrosal nerve / plexus of emissary veins. 6. Jugular foramen: Anteromedial part (transmits inferior petrosal venous sinus) / Posterolateral part (transmits internal jugular vein) / Middle part (9th, 10th, 11th cranial nerves) Anteromedial part Middle part Posterolateral part 7. Anterior condylar foramen (hypoglossal canal): Transmits Hypoglossal nerve (12th cranial nerve) / Meningeal branch of ascending pharyngeal artery / Emissary veins. 8. Foramen magnum: Transmits Lower end of medulla oblongata / Tonsils of cerebellum (right & left) / Spinal roots of accessory nerve (right & left) / Vertebral arteries / Spinal arteries (1 anterior & 2 posterior) / Vertebral plexus of veins / Meninges / Membrana tectoria / Apical ligament. 9. Inferior orbital fissure: Transmits Infra-orbital nerve and artery / Orbital branch of sphenopalatine ganglion / Zygomatic nerve / Emissary veins. 10. Squamo-tympanic fissure: Transmits Chorda tympani / Anterior tympanic artery. (3) Posterior part Forming bones: Squamous part of occipital bone. Squamous part of occipital bone  Bony features: 1. External occipital protuberance: A round elevation at midway between lambda and foramen magnum. 2. External occipital crest: A midline longitudinal ridge extends between external occipital protuberance and foramen magnum. 3. Superior nuchal line: A transverse ridge lateral to external occipital protuberance. 4. Inferior nuchal line: A transverse ridge extending laterally from the middle of external occipital crest. 5. Mastoid emissary foramen: Behind mastoid process. Transmits emissary veins.  External occipital crest Mastoid emissary foramen Inferior nuchal line External occipital protuberance Superior nuchal line  Definition: It is the inner surface of the base of the skull.  Parts: -Norma basalis interna is divided into 3 cranial fossae: 1. Anterior cranial fossa 2. Middle cranial fossa 3. Posterior cranial fossa Anterior cranial fossa Middle cranial fossa Posterior cranial fossa (1) Anterior cranial fossa Forming bones: -Anteriorly: Cribriform plate of ethmoid bone (at the middle) & orbital plates frontal bone (at both sides). -Posteriorly: Body of sphenoid bone (at the middle) & lesser wings of the sphenoid (at both sides). Orbital plate frontal bone Cribriform plate of ethmoid bone Body of sphenoid bone Lesser wings of the sphenoid  Bony features: 1. Frontal crest: Is a median bony elevation at the frontal bone. 2. The cribriform plate: Presents between the 2 orbital plates of the frontal bone. Separates the nasal cavities from the anterior cranial fossa. 3. Crista galli: A triangular vertical median crest on the upper surface of the cribriform plate. 4. Body of sphenoid bone: The part of body of sphenoid bone in the anterior cranial fossa is called “jugum sphenoidale”. Inside it the is the sphenoidal air sinus. 5. Anterior clinoid process: It is the process at the medial end of lesser wing of sphenoid.  Frontal crest Crista galli Cribriform plate Jugum sphenoidale Anterior clinoid process  Foramina: 1. Foramen cecum: Presents between frontal crest and crista galli. Closed by fibrous tissue. 2. Pores of cribriform plate: Transmit olfactory nerves from the olfactory areas of the nasal cavities to the olfactory bulbs of the brain. 3. Anterior ethmoidal foramen: Presents at the anterior part of cribriform plate. Transmits anterior ethmoidal nerve and vessels. 4. Posterior ethmoidal foramen: Presents at the posterior part of cribriform plate. Transmits posterior ethmoidal nerve and vessels.  Foramen cecum Site of anterior ethmoidal foramen Pores of cribriform plate Site of posterior ethmoidal foramen (2) Middle cranial fossa Forming bones: -At the middle: Part of body of sphenoid in the middle cranial fossa “called: sella turcica”. -At both sides: Greater wing of sphenoid bone, squamous part of temporal bone and anterior surface of petrous part of temporal bone. Sella turcica Greater wing of sphenoid bone Squamous part of temporal bone Petrous part of temporal bone  Appear at basalis interna Upper border Anterior surface Posterior surface Inferior surface Appear at basalis externa Surfaces of Petrous Part of Temporal Bone  Bony features: 1. Sella turcica: Is the saddle-like bony formation on the upper surface of the body of the sphenoid. It is composed of 3 parts: a. Hypophysial fossa (pituitary fossa): A median depression on the body of the sphenoid lodging the pituitary gland. b. Tuberculum sellae : A transverse median elevation in front hypophysial fossa. c. Dorsum sellae : A transverse median elevation behind hypophysial fossa. 2. Prechiasmatic sulcus: A median transverse depression in front tuberculum sellae. 3. Posterior clinoid process: It is the projecting lateral end of dorsum sellae. 4. Petrous part of temporal bone: It shows: a. Trigeminal impression: A depression at the apex of petrous part of temporal bone. It lodges the trigeminal ganglion. b. Arcuate eminence: An elevation posterolateral to trigeminal impression produced by superior semicircular canal of internal ear. c. Tegmen tympani: A flat area anterolateral to arcuate eminence forming the roof of middle ear.  Prechiasmatic sulcus Sella turcica Tuberculum sellae Hypophysial fossa Posterior clinoid process Dorsum sellae Trigeminal impression Tegmen tympani Arcuate eminence  Foramina: 1. Superior orbital fissure: Located between the greater and the lesser wings. It opens into the orbit. Transmits: Oculomotor nerve (3rd cranial nerve) / Trochlear nerve (4th cranial nerve) / Ophthalmic nerve / Abducent nerve (6th cranial nerve) / Ophthalmic veins. 2. Optic canal: Below the medial part of lesser wing of sphenoid. Transmits: Optic nerve (2nd cranial nerve) / Ophthalmic artery. 3. Foramen lacerum: Presents in front apex of petrous part of temporal bone. Transmits internal carotid artery at its upper part coming from the carotid canal, while its lower part is closed by a cartilage plate. 4. Foramen rotundum : Located posterior to the medial end of the superior orbital fissure. Transmits maxillary nerve. 5. Foramen ovale : A large foramen posterolateral to the foramen rotundum. Transmits: Mandibular nerve / Motor root of trigeminal nerve / Middle meningeal vein / Accessory meningeal artery / Lesser superficial petrosal nerve / Emissary veins. 6. Foramen spinosum: Located posterolateral to the foramen ovale. Transmits: Middle meningeal artery / Nervous spinosum.  Optic canal Superior orbital fissure Foramen rotundum Foramen lacerum Foramen ovale Foramen spinosum (3) Posterior cranial fossa Forming bones: -Occipital bone (its basilar, 2 lateral and squamous parts) -Body of sphenoid bone. -Posterior surface of petrous part of temporal bone. -Mastoid part of temporal bone. Body of sphenoid bone Basilar part of occipital bone Petrous part of temporal bone Mastoid part of occipital bone Lateral part of occipital bone Squamous part of occipital bone  Bony features: 1. Clivus: The sloping median part in front the foramen magnum. Formed of body of sphenoid and basilar part of occipital bone. 2. Internal occipital protuberance: A median round projection at squamous part of occipital bone. 3. Internal occipital crest: A median longitudinal bony ridge extending between internal occipital protuberance and foramen magnum. 4. Transverse sulcus: A broad transverse groove extending laterally from the internal occipital protuberance. 5. Sigmoid sulcus: A broad groove extends as a downward S-shaped extension from transverse sulcus on the mastoid part of temporal bone. It ends at the site of jugular foramen. 6. Superior petrosal sulcus: A groove along the superior border of petrous part of temporal bone. 7. Inferior petrosal sulcus: A groove along the petro- occipital junction.  Inferior Clivus petrosal sulcus Petro-occipital junction Superior Superior petrosal sulcus border of petrous part of temporal bone Sigmoid sulcus Internal occipital crest Internal occipital protuberance Transverse sulcus  Foramina: 1. Internal auditory meatus: At the posterior surface of petrous part of temporal bone. Transmits: Facial nerve (7th cranial nerve) / Vestibulocochlear nerve (8th cranial nerve) / Internal auditory vessels. 2. Jugular foramen: At the petro-occipital junction. Transmits: Anteromedial part (transmits inferior petrosal venous sinus) / Posterolateral part (transmits internal jugular vein) / Middle part (9th, 10th, 11th cranial nerves). 3. Anterior condylar foramen (hypoglossal canal): Presents above the occipital condyle. Transmits: Hypoglossal nerve (12th cranial nerve) / Meningeal branch of ascending pharyngeal artery / Emissary veins. 4. Foramen magnum: Between the 2 occipital condyles. Transmits Lower end of medulla oblongata / Tonsils of cerebellum (right & left) / Spinal roots of accessory nerve (right & left) / Vertebral arteries / Spinal arteries (1 anterior & 2 posterior) / Vertebral plexus of veins / Meninges / Membrana tectoria / Apical ligament. Intenal auditory meatus Anterior condylar foramen Jugular foramen Foramen Magnum