CHAPTER 7 â THE AXIAL SKELETON
â The skeleton consists of:
o Bones ï 206 of them in the human skeleton. Grouped into:
ï§ Axial skeleton
ï§ Appendicular skeleton
o Joints/articulations ï junctions between skeletal muscles
o Ligaments ï connect bones and reinforce most joints
â Forms the long axis of the body.
â Consists of 80 bones divided into: skull, vertebrate column and thoracic cage
â Bodyâs most complex bony structure.
o Facial bones form anterior aspect; cranium forms the rest
o Cranium can be divided into:
ï§ Cranial vault/calvaria/skullcap ï forms superior, lateral and
posterior aspect of the skull and the forehead region
ï§ Cranial base/floor ï forms the inferior part
â¢ Internally, prominent bony ridges divide the cranial base
into 3 distinct steps/fossae ï anterior, middle and posterior
cranial fossae (all completely enclosed by cranial vault).
o Brain occupies cranial cavity.
o Skull also contains smaller cavities:
ï§ Middle and inner ear cavities ï carved into lateral aspects of
ï§ Nasal cavities ï lies in and posterior to nose
ï§ Orbits ï house eyeballs
ï§ Paranasal sinuses ï air-filled sinuses that occur in several bones
around the nasal cavity.
o Skull has ~85 named openings (foramina, canals, fissures)
ï§ Provide passageways for spinal cord, major blood vessels serving
the brain, and 12 cranial nerves.
â¢ Foramen magnum is the opening for spinal cord.
â Formed by:
â Cranial bones (8) ï does not mean skull! Enclose and protect the brain. They are
attachment points for some head and neck muscles.
ï§ Temporal bones
â¢ Lies inferior to parietal bones and forms inferolateral region
of skull and parts of cranial floor.
â¢ 1 region to start getting grey hair with age.
â¢ Each has 4 major regions: o Squamous ï has zygomatic process, which
together with zygomatic bone forms zygomatic arch
ï§ Mandibular fossa on inferior surface of
zygomatic process receives mandible and
forms the temporomandibular/jaw joint.
o Tympanic ï surrounds external acoustic
meatus/external ear canal.
ï§ Styloid process projects inferiorly from
tympanic region and is attachment point for
tongue muscles and pharynx, and for
ligament connecting skull to hyoid bone of
o Mastoid ï has mastoid process, an anchoring site
for some neck muscles.
ï§ Stylomastoid foramen is located between
styloid and mastoid processes and a branch
of cranial nerve VII leaves skull through it.
ï§ Also has air sinuses called mastoid air cells.
o Petrous (rocky process) ï projects medially and
contributes to cranial base. Posterior slope lies in
posterior cranial fossa, while anterior slope is in the
middle cranial fossa, the fossa holding the temporal
lopes of the brain.
ï§ Middle and inner ear cavities lie in this
region, which contain sensory apparatus for
hearing and balance.
ï§ Jugular foramen located in this region,
through which jugular vein (largest vein of
the head) passes through.
ï§ Parietal bones
â¢ Bulk of cranial vault; most superior part and its lateral
â¢ Has 4 large sutures where it articulates with other cranial
o Coronal ï occurs anteriorly, where it meets frontal
o Squamous ï occurs where it meets temporal bone
inferiorly on lateral aspect of the skull
o Sagittal (midline) ï where right and left parietal
bones meet superiorly in middle of cranium
o Lambdoid ï occurs where it meets occipital bone
superiorly (looks like Greek letter lambda, ï ).
ï§ Frontal bone
â¢ Forms forehead; roofs of orbits
o Supraorbital margin of each orbit is pierced by a
hole/notch called supraorbital foramen/notch. ï§ Transmits supraorbital nerve and artery,
which supply the forehead
â¢ Contributes internally to anterior cranial fossa ï holds large
frontal lobes of brain
â¢ Glabella ï region with no hair in between eye brows
â¢ Contains frontal sinus (air-filled) lateral to glabella
ï§ Occipital bone
â¢ Posterior portion of cranium and cranial base
â¢ Articulates with temporal bones at the occipitomastoid
sutures and with the parietal bones at the lambdoid suture
â¢ Internally forms posterior cranial fossa ï holds cerebellum
â¢ Foramen magnum located at its base ï connects with spinal
o Occipital condyles ï articulates with 1 vertebrate;
enables head to nod âyesâ
o External occipital protuberance ï knob in the
midline; connects neck vertebrae to skull
o Superior and inferior nuchal lines ï tendons and
musculature attach; superior marks the upper limit
of the neck.
o Hypoglossal canal ï for cranial nerve
XII/hypoglossal nerve (important exit point)
ï§ Sphenoid bone
â¢ Looks like butterfly; spans width of cranial floor
â¢ Articulates with every other cranial bone
â¢ Consists of a central body and 3 pairs of processes:
o Greater wings ï projects laterally forming parts of
middle cranial fossa and the orbit.
o Lesser wing ï horn-shaped; forms part of floor of
anterior cranial fossa and part of orbit
o Pterygoid process ï projects inferiorly from greater
â¢ Superior part of body has saddle-shaped prominence
called sella turcica (Turkish saddle)
o Hypophyseal fossa (seat of saddle) holds pituitary
â¢ Contains sphenoid sinuses within the sphenoid body
â¢ Has 5 openings for cranial nerves
ï§ Ethnoid bone
â¢ Lies between nasal and sphenoid bones
â¢ Forms most of the medial bony region between nasal
cavity and orbits
â¢ Most deeply situated bone of the skull. â¢ Superior surface formed by paired, horizontal cribriform
plates that are perforated by tiny holes called olfactory
o Crista galli ï superior projection between the 2
cribriform plates in the midline.
â¢ Superior and middle nasal conchae extend medially from
lateral masses and protrude into nasal cavity.
â Facial bones (14) ï Provides: framework for face; cavities for the sense organs;
openings for air/food passage; teeth anchor; attachment for facial muscles.
ï§ Maxillary bones/maxilla
â¢ Forms upper jaw and central part of facial skeleton
â¢ Articulates with all other facial bones except mandible.
â¢ Contains maxillary sinuses (largest paranasal sinus)
â¢ Forms part of inferior orbital fissure
â¢ Palatine process projects medially from alveolar margins ï
forms anterior region of hard palate
ï§ Zygomatic bones/cheek bones
â¢ Posteriorly ï joins zygomatic process of temporal bone
â¢ Superiorly ï joins zygomatic process of frontal bone
â¢ Anteriorly ï joins zygomatic process of maxilla
ï§ Nasal bones
â¢ Join medially to form bridge of nose.
â¢ Superiorly ï articulate with frontal bone
â¢ Laterally ï join with maxilla
â¢ Posteriorly ï join with perpendicular plate of ethnoid bone
â¢ Inferiorly ï attach to cartilage that form most of skeleton of
ï§ Lacrimal bones
â¢ Located in medial orbital walls; contain lacrimal fossa that
contain lacrimal sac that gathers tears.
â¢ Superiorly ï articulate with frontal bone
â¢ Posteriorly ï join with ethmoid bone
â¢ Anteriorly ï join with maxilla
ï§ Palatine bones
â¢ Lie anterior to maxilla
â¢ Articulate with each other at their inferior horizontal plates ï
complete posterior part of hard palate
â¢ Perpendicular plates form posterior part of lateral walls of
ï§ Inferior nasal concha
â¢ Largest of he three pairs of conchae; lie inferior to middle
nasal conchae of the ethmoid bone.
o Unpaired ï§ Mandible
â¢ Lower jaw bone; largest, strongest facial bone
â¢ Articulates with temporal bone
â¢ Composed of 2 main parts:
o Horizontal body ï anchors lower teeth and forms
ï§ Superior border is alveolar margin ï tooth
sockets (alveoli) open into it.
ï§ Anteriorly, fusion between 2 halves of
mandible is called mental protuberance.
o 2 upright rami/ramus ï meet body posteriorly at a
ï§ 2 processes at superior margin of each
â¢ Coronoid process ï temporalis
muscle that elevates mandible
â¢ Condylar process ï forms
mandiblular condyle/head of