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Norma Basalis OBJECTIVES At the end of this lecture, students will be able to:• Bones forming the base of skull • Narrate the details of anterior, middle and posterior part of base of skull • Identify different foramina and structures passing through them at the base • Explain the attachments and relations of base of skull Inferior Aspect of Skull • Formed by – Palatine processes of maxilla – Horizontal plate of palatine bones – Vomer – Pterygoid processes, inferior surfaces of great wings, spinous processes & part of body of sphenoid – Inferior surfaces of squamae & petrous portions of temporals – Inferior surface of occipital bone The Adult Skull (Inferior View) Anterior Part • Formed principally by hard palate, which is bounded anteriorly & laterally by alveolar arch • Incisive fossa – Lateral incisive foramina (of Stenson) which continue as incisive canals & transmit terminal branches of greater palatine vessels & nasopalatine nerves from nasal cavity – Median incisive foramina (of Scarpa) transmit nasopalatine nerves when present • Depressions for palatine glands • Cruciate suture Ventral Skull Ventral Skull palatine process sphenoid bone palatine bone vomer bone styloid process temporal bone mastoid process external occipital protuberance occipital bone Palatine Process • The palatine process of the maxilla (palatal process), thick and strong, is horizontal and projects medialward from the nasal surface of the bone. • It forms a considerable part of the floor of the nose and the roof of the mouth and is much thicker in front than behind. Incisive Foramen • When the two maxillæ are articulated, a funnel-shaped opening, the incisive foramen, is seen in the middle line, immediately behind the incisor teeth. Anterior Part • Greater palatine foramen – For transmission of greater palatine vessels & nerve, which descend in greater palatine canal from pterygopalatine fossa • Lesser palatine foramina – Pyramidal process of palatine bone, perforated by one or more foramina through which course lesser palatine vessels & nerve to soft palate – Transverse ridge for attachment of tendinous expansion of tensor veli palatini muscle • Posterior nasal spine, on which attaches musculus uvulae • • • • • Middle Part Commences just behind hard palate & extends to level of anterior border of foramen magnum. Choanae Medial pterygoid plate – Scaphoid fossa for origin of tensor veli palatini muscle – Pterygoid hamulus, around which tendon of tensor veli palatini muscle turns Lateral pterygoid plate – Its lateral surface affords attachment to pterygoideus lateralis muscle Pharyngeal tubercle – Near center of basilar portion of occipital bone – For attachment of fibrous raphe of pharynx – Depressions on each side for insertions of rectus capitis anterior & longus capitis • Foramen ovale – At base of lateral pterygoid plate – Through which passes mandibular nerve, accessory meningeal artery, & lesser petrosal nerve • Sphenoidal spine – Lateral to foramen ovale – Attachment to sphenomandibular ligament & tensor veli palatini • Foramen spinosum – Posterior & somewhat lateral to foramen ovale – Transmits middle meningeal vessels & small meningeal branch of mandibular nerve • Mandibular fossa – Lateral to sphenoidal spine – Divided into 2 parts by petrotympanic fissure – Anterior portion - concave, smooth, & bounded in front by articular tubercle - articulates with condyle of mandible. – Posterior portion is rough & bounded behind by tympanic part of temporal bone. Middle Part • Foramen lacerum – At base of medial pterygoid plate in dried skull – Irregular in shape & variable in size – Not complete foramen in intact body, because its inferior part is covered over by fibrocartilaginous plate, across superior (inner or cerebral) surface of which passes internal carotid artery. – Boundary - In front by great wing of sphenoid - Behind by apex of petrous portion of temporal bone - Medially by body of sphenoid & basilar portion of occipital bone • Carotid canal – Inferior surface of petrous temporal bone is pierced by round opening. – Internal carotid artery, coursing within canal, immediately takes right angle turn to reach side of foramen lacerum. • Quadrilateral surface – Rough surface near apex of petrous portion of temporal bone, lateral to which is orifice or entrance of carotid canal. – Attachment to levator veli palatini • • Sulcus tubae auditivae – Lateral to foramen lacerum, between petrous part of temporal & great wing of sphenoid – Lodges cartilaginous part of auditory tube which is continuous with bony part within temporal bone – Petrosphenoidal fissure at bottom of this sulcus • • • • Posterior Part Formed principally by occipital bone Mastoid process – Mastoid notch on medial side of each process, for posterior belly of digastricus – Occipital groove medial to mastoid notch, for occipital artery Styloid process – Medial & slightly anterior to mastoid processes Stylomastoid foramen – At base of styloid process – Facial nerve exits toward side of face, & stylomastoid artery enters to tympanic cavity. • • Jugular foramen – Medial to styloid process & posterior to carotid canal – Anterior compartment – inferior petrosal sinus – Intermediate – glossopharyngeal, vagus, & accessory nerves – Posterior – sigmoid sinus which leads to internal jugular vein, & some meningeal branches from occipital & ascending pharyngeal arteries • Petro-occipital fissure – Extending anteriorly from jugular foramen to foramen lacerum carotid canal jugular foramen occipital condyle foramen magnum Occipital bone Occipital bone Posterior Part • Foramen magnum – Posterior to basilar portion of occipital bone – Transmit - Medulla oblongata & its membranes - Accessory nerves - Vertebral arteries - Anterior & posterior spinal arteries - Ligaments connecting occipital bone with axis Occipital condyles – By which foramen magnum is bounded laterally – On medial surfaces of which attach alar ligaments – Articulate with superior articular surfaces overlying lateral masses of atlas • Jugular process – Lateral to each occipital condyle – Attachment for rectus capitis lateralis muscle & lateral atlantooccipital ligament • Hypoglossal canal – Courses forward & laterally from inner aspect of occipital bone within cranium just above foramen magnum to opening that perforates occipital bone externally at lateral part of base of occipital condyle – Transmits hypoglossal nerve & a branch of posterior meningeal artery • Condyloid fossa – Posterior to each occipital condyle – Perforated on one or both sides by condyloid canal, for transmission of a vein from sigmoid sinus to vertebral veins in upper cervical region • External occipital crest • External occipital protuberance • Superior & inferior nuchal lines Thankyou