Norma Basalis OBJECTIVES At the end of this lecture, students will ...

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
• Formed by
Inferior Aspect of Skull
– 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
palatine process
palatine bone
vomer bone
temporal bone
external occipital
protuberance
Ventral Skull
Ventral Skull
sphenoid bone
Palatine Process
styloid process
mastoid process
occipital bone
• 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
foramen magnum
Occipital bone
occipital
condyle
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