Norma Basalis

Subdivided into 3 parts: Its divided by two imaginary lines • The anterior line: passing along the posterior border of the hard palate. • The posterior line: passing through the posterior border of the foramen magnum.  Anterior part of the norma basalis  Formed by : • Hard palate • Bounded anteriorly and laterally by alveolar arch of maxilla.  Bones forming : • Palatine process of maxilla • Horizontal plate of palatine bone  Sutures: • Palato-maxillary suture • Inter-maxillary suture  Some important features • Alveolar margin (arch) : carries 16 sockets for the roots of upper teeth. • Posterior border of the hard palate • Posterior nasal spine • Maxillary tuberosity  Foramina in the anterior part • Incisive fossa ( contain 4 small foramina )  2 small median incisive foramina  2 lateral foramina • Greater palatine foramen (Medial to the last molar ) • Lesser palatine foramina 1  Middle part of norma basalis  Extended from the posterior border of the hard palate to the line passing through the anterior border of the foramen magnum.  Divided into : Median area , Lateral area  Bone forming it : • Anterior ( middle) : vomer and body of sphenoid • Anterior (lateraly ) :Ptytegoid process and infra temporal surface of greater wing of sphenoid . • Posterio-lateraly :  Petrous part of temporal bone  Tympanic part of temporal bone  Mastoid part of temporal bone • Posteriorly in the middle  Basilar part of occipital bone  2 lateral parts of occipital bone  Important particular features • Posterior nasal openings (choana): separated from each other by vomer. • A median vertical bony plate intervening between the 2 posterior nasal opening. Pterygoid process of Infratemporal surface of Petrous part of temporal sphenoid bone greater wing of sphenoid bone *Lateral pterygoid plate •Bounded laterally by *Is wedged between greater *Medial pterygoid plate infra temporal crest. wing of sphenoid and basilar (posterior border) •Bounded medially by part of occipital bone. pterygoid hamuls the groove for the *Contains : (upper end) pharyngo-tympanic tube • Foramen lacerum scaphoid fossa •It shows the spine of • Rough quadrate area *Pterygoid fossa in sphenoid and two • Carotid canal between which is a V foramen (oval and • Jagular foramen shape spinosum) *It shows two processes : Styloid , Mastoid process 2  Basilar part of occipital bone  Important features • Pharyngeal tubercle • Articular parts (mandibular fossa, articular eminence, occipital condyle) • Hypoglossal canal • Posterior Condylar fossa • Posterior Condylar canal Cranial Cavity (A) INNER SURFACE OF SKULL CAP (B) NORMA BASALIS INTERNA (A) INNER SURFACE OF SKULL CAP  Bones: • Anteriorly: Frontal bone • On the sides: parietal bones • Posteriorly: squamous part of occipital bone Sutures: Coronal, Sagittal & Lambdoid.  Particular Features: 1. Frontal crest 2. Sagittal sulcus 3. Granular foveolae 4. parietal emissary foramen 5. Grooves for branches of middle meningeal vessels. (B) NORMA BASALIS INTERNA Divided into 3 Cranial Fossae:  Ant. cranial fossa  Middle cranial fossa  Post. cranial fossa 3 Anterior cranial fossa The highest, smallest & most anterior one. Boundaries: Anteriorly and laterally The frontal bone Posteriorly - lesser wings of the sphenoid bone Bones forming the floor of the fossa: Anteriorly: 1. Orbital plates of frontal bone 2. Cribriform plate of ethmoid bone Posteriorly: 1. lesser wings of sphenoid 2. Jugum sphenoidal (ant. part of body of sphenoid) 4 Middle cranial fossa It lies below the Ant. fossa & has a butter-fly shape. The Middle Cranial Fossa is formed by: 1. Body of sphenoid 2. Greater wing of sphenoid 3. Petrous part of temporal bone Boundaries: Anteriorly: post borders of lesser wings of sphenoid & ant. clinoid processes. Posteriorly: sup. borders of petrous temporal bones & dorsum sellae. Bones forming its Floor: Median part: Sella turcica (Turkish Saddle) formed by the body of sphenoid. On either side: (1) greater wing of sphenoid: anteriorly. (2) Petrous temporal bone: posteriorly. (3) Squamous temporal bone: laterally. Posterior cranial fossa The widest, deepest & most post of the 3 fossae. Bones forming its floor: Anteriorly: The clivus Posteriorly: Squamous part of occipital bone Antro-laterally: Petrous part of temporal bone ,mastoid part of temporal bone