Norma Basalis

1. Norma Basalis

2. 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

4. 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

6. 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

9. 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 topterygoideus lateralis muscle

10. Middle Part • 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

13. Middle Part • 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.

15. 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

16. Middle Part • 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

17. Middle Part • 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

20. 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.

21. Posterior Part • 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

23. 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 • Basion • Opisthion

26. Posterior Part • 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 atlanto-occipital ligament

27. Posterior Part • 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

29. Posterior Part • External occipital crest • External occipital protuberance • Superior & inferior nuchal lines