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Wednesday 8/13/03 1 P.M.
Heath White PDF
Eric Lawrence
Page 1 of 5
Arthrology of the Cranium
5 Principles to Know and Understand their Mechanisms
 The inherent motility of the brain and spinal cord
 The fluctuation of the cerebrospinal fluid
 The mobility of the intracranial and intraspinal membranes
 The articular mobility of the cranial bones (covered in this lecture, but all overlap)
 The involuntary mobility of the sacrum between the ilia
Sutherland’s Epiphany
“like a blinding flash of light came the thought: beveled like the gills of a fish and
indicating articular mobility for a respiratory mechanism.”
Functions of the Cranium
1. Encases and protects the CNS
2. Protects and supports the organs of special senses
3. Provides rigid isolation for the cerebral circulatory system
Bones of Skull are divided into 2 categories:
Sphenoid, Occiput, Ethmoid, Frontals, Temporals, and Parietals
Facial Skeleton: Zygomatics, Palatines, Maxillae, Vomer, Lacrimals, Nasals, Inferior
Conchae, and Mandible
Development of the Bones of the Skull
-developed from the mesenchyme
1. Neurocranium = protective case for the brain
2. Viscerocranium = facial skeleton
-neurocranium and viscerocranium are broken down further (functional division)
a. membranous – ossification of mesenchyme
b. cartilaginous – endochondrial formation
1. Cartilaginous Neurocranium
-forms base of the skull
-body of occiput (basilar which includes the SBS region, condylar, and supraocciput)
-body of sphenoid
-petromastoid portion of temporal
-formed under compressive forces – support for base of skull
-more dense than membrane
-origin of the mobility for cranial mechanism and skull
2. Membranous Neurocranium
-makes up calvaria
-frontals and parietals
-squamous portions of occiput, sphenoid, and temporal bones
-formed to accommodate for the motion in the cartilaginous portion
-thinner bone and more sutures found here
-allow for molding of fetal skull (to fit out of pelvic canal)
3. Cartilaginous Viscerocranium
-derived from pharyngeal arches
-not much importance for cranial mechanism
-1st Arch forms  malleus and incus
-2nd Arch forms  stapes, styloid process of temporal bone
Wednesday 8/13/03 1 P.M.
Heath White PDF
Eric Lawrence
Page 2 of 5
4. Membranous Viscerocranium
-intermembranous ossification of maxillary prominence of 1st pharyngeal arch
-further forms: squamous portion of temporal bone, maxillae, zygomatics, nasal bones,
and mandible
-squamous portion of temporal bone is originally formed in membranous viscerocranium,
but is considered later in neurocranium because of it’s relationship with the vault
Sutures that Separate the Bones
Classification of Sutures:
1. synarthrosis – a continuous binding substance
a. synchrondrosis – a cartilaginous union
eg/ at SBS where sphenoid and occiput articulate
b. suture – fibrous tissue uniting margins of bones in the skull
i. composed of 5 layers
ii. continuous outer border of periosteum and inner border
where periosteum forms fibrous capsule
iii. fibrous tissue in center (with nerves, vessels and weak fiber
iv. like a synovial joint
Types of Sutures
Serrated – saw toothed - sagittal
Squamous – scale like - squamoparietal
Harmonic – edge to edge, eg/ lacrimoethmal joint
Gomphosis – peg and socket eg/ greater wing w/ body
c. syndesmosis – ligamentous union, eg/ temporasphenoid joint
2. Diarthrosis – a joint cavity, eg/ TMJ
Premature suture closure
Growth of bone becomes parallel with closed suture and inhibited at 90o
Eg/ closure of coronal suture  growth is lateral  wide head
Beveling = what allows bones to articulate and move and accommodate to motion
Slope overlaps “like gills of a fish”
Eg/ The external bevel of the parietal bone allows the temporal bone to move laterally
during flexion/external rotation
-Histology suggests that there is active bone growth at sutures and there is movement at sutures
Wormian Bones = island bones
Most often found in the lambda (between parietal and occiput)
A source for accommodation of more motion
-when motion is lost at one place it’s gained at another place
Inherent Motility of Brain and Spinal Cord
-As neural tube forms it begins to move forward in a vermiform motion,( like a worm),
shrinking in and contracting out,
-neural tube grows faster than the skull can grow
-grows in an anterior direction and bifurcates into 2 cerebral hemispheres
-when it reaches the front of the skull it moves superiorly and a posterior direction
-turns again inferiorly and curls back anterolaterally to form temporal lobes
-as it coils it expands laterally and flexion/extension occurs
Based upon this inherent motility is how bones form and are shaped
-falx cerebri and tentorium cerebelli form a V-shape that encloses sinuses
- as contraction occurs, V-shape spreads in and out and pumps sinuses
Wednesday 8/13/03 1 P.M.
Heath White PDF
Eric Lawrence
Page 3 of 5
Reciprocal Tension Membrane
-Falx cerebri and tentorium cerebelli form 3 sickle-shaped membranes originating from
bones and go anteriorly to form Sutherland’s fulcrum, then proceed to sacrum
-falx attaches anteriorly to crista galli of ethmoid
-proceeds posteriorly along saggiltal sinus to internal occipital protuberance
-tentorium cerebelli attaches posteriorly to Sutherland’s fulcrum and to internal occipital
protuberance and anteriorly to the anterior and posterior clinoid processes
-reciprocal tension membrane drives the motion of the cranial bones
Principles of Motion
Midline Bones = sphenoid, occiput, vomer and ethmoid
-rotate around transverse axis
-driven by the sphenoid
-flexion and extension motion (or inhalation and exhalation)
Paired Bones = parietals, frontals, temporals, zygomae, maxillae, nasals, lacrimals,
-external and internal rotation (or inhalation and exhalation)
 Flexion
-SBS is red circle
- with flexion SBS will rise
-ant. portion of sphenoid falls forward
-greater wing will go anterior and inferior
-occiput curves under
-basal portion comes up with posterior
portion of spheoid
-sphenoid drives ethmoid to rotate with posterior
-vomer moves inferiorly
-palatines flatten
-as SBS rises dura gets pulled up and base of
sacrum is moved in posterior superior direction
-opposite of flexion
-SBS is falling
-occiput curls outward
-sphenoid rotates superiorly on anterior border
-drives ethmoids on opposite direction as flexion
-vomer moves back superiorly
--movement of the bones in flexion and extension are like gears in their movement upon one
another, and they are all being driven by the sphenoid
Calvarium Bones
1. Sphenoid
-most important bone of the calvarium
-responsible for movement directly or indirectly
-consists of 4 parts: body, greater wing, lesser wing, and pterygoid process
-each have their own motion with flexion and extension
-articulates with 12 bones – know where these are at and how it drives them
-sphenoid forms anterior, middle, and posterior fossa
Wednesday 8/13/03 1 P.M.
Heath White PDF
Eric Lawrence
Page 4 of 5
-forms temporal and infratemporal fossa
-nasal fossa and portion of orbits
-the pterion is the one part that is palpated externally
Rotation is on a transverse axis located anterior and on level of the floor of the
sella turcica
2. Occiput
-driven by sphenoid
-it moves temporals and parietals
-multiple centers of ossification
1 – basilar – from cartilaginous bone
2 – condylar – from cartilaginous bone
2 – supraocciput – from cartilaginous bone
1 – intraparietal – forms from membranous bone (part of vault)
Parts of Occiput:
basilar – forms SBS, ant. ¼ of condyles and ant. foramen magnum
condylar – post ¾ of condyles, hypoglossal canal, remaining portion of
foramen magnum
squamous – sup and inf nuchal lines, sagittal ridge for falx cerebri and
cerebelli, horizontal ridge for tentorium, and sinuses within
-articulations – parietals, temporals, sphenoid, and atlas
Rotation on transverse axis just above jugular process of occiput at level
of SBS
3. Ethmoid
-driven by sphenoid
-transverse axis
-crista galli is located superiorly
-2 lateral masses that flare out with flexion
-perpendicular plate and cribriform plate – each moves in specific way
4. Frontals
-originate as paired bones and ossify at 6 yrs old
-10% of population has patent suture or a remnant
-axis of rotation is through the center of orbital plate and through frontal
eminence and bends out into external rotation
-anterior margins go into an anterolateral direction
5. Temporals
-moved by occiput
-axis of motion is through petrous ridge and converges in anteromedial
-spins into external and internal rotation
-squamous portion moves in anterolateral direction
-mastoid tip moves posteromedially
-mastoid portion moves anterolateral
-mandibular fossa moves posteromedially
6. Parietals
-moved by temporals and occiputs by combined motion
-axis is different for different people
-lateral to the bregma on coronal suture in posterolateral direction
-mastoid and sphenoid angles rotate in anterolateral direction
-sagittal margins depress,so in flexion, vertical section goes down
Wednesday 8/13/03 1 P.M.
Heath White PDF
Eric Lawrence
Page 5 of 5
Facial Skeleton
1. Zygomatics
-paired bones
-with flexion – moves into external rotation and orbit widens
-moved by sphenoid
-acts as pump to promote circulation through maxillary sinus
2. Maxilla
-forms anterior 2/3 of palate
-axis through midincisal line – rotates into external rotation around line
3. Palatines
-forms posterior 1/3 of palate
-follows maxilla in motion (moved directly by sphenoid)
-paired bones
-in external rotation – horizontal plate moves posterior inferior and flattens out
posterior portion of palate
4. Vomer
-directly articulates with sphenoid
-around transverse axis
-sphenoid falls anterior  drives vomer anterior inferior
-actually 2 plates smashed together
-toward sphenoid it flattens into a cuplike shape that sphenoid sits in
-plunger like action promotes circulation of sphenoid sinus
Driving Mechanism of Facial Bones
-directly or indirectly from sphenoid
-know the direct mechanisms