The Axial Skeleton Eighty bones segregated into three regions

The Axial Skeleton 

Eighty bones segregated into three regions 

Skull 

Vertebral column 

Bony thorax 

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Bones of the Axial Skeleton 

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings 

Figure 7.1

The Skull 

The skull, the body’s most complex bony structure, 

is formed by the cranium and facial bones (22 in 

all) 

Cranium 

Made up of cranial bones 

protects the brain and is the site of attachment for 

head and neck muscles 


Facial bones 

Facial bones 

Form the framework of the face 

Contain cavities for special sense organs (smell, 

sight, taste, hearing) 

Provide openings for the passage of air and food 

Secure the teeth 

Anchor the facial muscles of expression 


Bones of the Skull 

Most of the bone of the skull are flat bones 

All of the bones of the skull are tightly united by 

sutures (interlocking joints)…except the mandible 


Major Skull Sutures 

Sutures of the skull connect the cranial bones 

The major sutures of the skull are: 

Coronal 

Sagittal 

Squamous 

Lambdoid 

w/ other sutures connecting the facial bones 


Overview of Skull Geography 

The cranium can be divided into a vault and a base 

The cranial vault (calvarin) forms the superior, 

lateral, and posterior aspects of the skull (and 

forehead) 

The cranial base (floor) forms the skull’s inferior 

aspect 



The internal bony ridges divide the base into 3 

steps (or fossae): 

Anterior cranial fossae 

Middle cranial fossae 

Posterior cranial fossae 

The brain sits within these 3 cranial fossae 



Other cavities include: 

Middle & internal ear cavities 

Nasal cavity 

Orbits 

sinuses 


Anatomy of the Cranium 

Eight cranial bones 

Parietal (2) 

Temporal (2) 

Frontal 

Occipital 

Sphenoid 

Ethmoid 

The curvatures of the cranial bones makes them strong and 

allows them to be thin (e.g. an eggshell) 


Frontal Bone 

Forms the anterior portion of the cranium 

Articulates posteriorly with the paired parietal bones via the coronal 

suture 

Most anterior part is the vertical frontal squama (otherwise known as the 

“forehead”) 

The frontal squama ends inferiorly at the supraorbital margins 

The supraorbital margin is pierced by the supraorbital foramen 

allowing passage of the supraorbital artery and nerve to the 

forehead 

Extending posteriorly, the frontal bone forms the superior wall of the 

orbits and the anterior cranial fossa 

The glabella is the smooth part of the bone between the orbits 

The frontonasal suture joins the glabella and the nasal bones 

The frontal sinuses are found deep and lateral to the glabella 


Frontal Bone 


Figure 7.2a

Parietal Bones and Major Associated Sutures 

The parietal bones form the superior and lateral aspects of the 

skull 

They make up the bulk of the cranial vault 

The 4 largest sutures are associated with the parietal bones: 

Coronal suture – articulation between parietal bones 

and frontal bone anteriorly 

Sagittal suture – where right and left parietal bones 

meet superiorly 

Lambdoid suture – where parietal bones meet the 

occipital bone posteriorly 

Squamosal or squamous suture – where parietal and 

temporal bones meet 


Parietal Bones and Major Associated Sutures 

Form most of the superior and lateral aspects of the 

skull 


Figure 7.3a

Occipital Bone and Its Major Markings 

The occipital bone forms most of the skulls posterior wall and base 

It articulates anteriorly w/ the paired parietal and temporal bones via the 

lambdoid and occipitomastoid sutures, respectively 

It articulates w/ the sphenoid bone via the basioccipital plate 

Internally, the occipital bone forms the walls of the posterior cranial fossa 

The foramen magnum found at the base of the occipital bone if where the 

inferior part of the brain connects with the spinal cord 

The occipital condyles flank the foramen magnum laterally and articulate w/ 

the first vertebra permitting a “nodding” movement 

The external occipital proturbence (can you feel yours??) 

External occipital crest: secures the legamentum nuchae (an elastic ligament 

that connects the vertebrae to the skull) 

Superior & inferior nuchal lines: anchor many muscles of the neck & back 


Occipital Bone and Its Major Markings 

Forms most of skull’s 

posterior wall and base 

Major markings 

include the posterior 

cranial fossa, foramen 

magnum, occipital 

condyles, and the 

hypoglossal canal 


Figure 7.2b

Temporal Bones 


Figure 7.5

Temporal Bones 

Lie inferior to the parietal bones and join them at 

the squamous sutures 

Form the inferolateral aspects of the skull and parts 

of the cranial floor 

Divided into four major regions 

Squamous 

Tympanic 

Mastoid 

petrous 


Temporal Bones: Squamous Region 

The squamous region has the bar-like zygomatic 

process that meets the zygomatic bone forming the 

zygomatic arch (the cheek bone) 

The mandibular fossa on the inferior surface of the 

zygomatic process receives the condyle of the 

mandible (lower jawbone) forming the 

temporomandibular joint 


Temporal Bones: Tympanic Region 

The Tympanic region surrounds the external 

acoustic meatus (external ear canal) 

Inferior to the exteranl acoustic meatus lies the 

styloid process, an attachment point for several 

tongue and neck muscles 


Temporal Bones: Mastoid Region 

The mastoid region contains the large mastoid 

process which anchors some neck muscles 

Feel it right behind your ear…go ahead, feel it! 

The stylomastoid foramen allows cranial nerve VII 

(the facial nerve) to leave the skull 


Temporal Bones: Petrous Region 

The petrous region contributes to the cranial base 

It lies between the occipital bone and the sphenoid 

bone 

Together w/ the sphenoid bone they form the 

middle cranial fossa which supports the temporal 

lobes of the brain 

This region also houses the middle & internal ear 

cavities 


Temporal Bones: Petrous Region 

Several foramen penetrate the petrous region: 

-the jugular foramen: internal jugular & 3 cranial nerves 

-the carotid canal: internal carotid artery 

-the foramen lacerum 

-the internal acoustic meatus: cranial nerves VII & VIII 

-the foramenia rotundum, ovale, and spinosum 


Sphenoid Bone 

Butterfly-shaped bone that spans the width of the 

middle cranial fossa 

The Keystone Bone: Forms the central wedge that 

articulates with all other cranial bones 

Consists of a central body, greater wings, lesser 

wings, and pterygoid processes 

Contains the sphenoid sinuses 


Sphenoid Bone 

The superior surface bears the sella tucica which 

bears the hypophyseal fossa that forms the 

enclosure for the pituitary gland 

The hypophyseal fossa is abutted anteriorly by the 

tuberculum sellae and posteriorly by the dorsum 

sellae, which terminates in the posterior clinical 

processes 


Sphenoid Bone 


Figure 7.6a

Sphenoid Bone 


Figure 7.6b

Sphenoid Bone 

The greater wings project laterally from the body and form: 

Middle cranial fossa 

Dorsal walls of the orbits 

External wall of the skull (medial to the zygomatic arch) 

The lesser wings form: 

Part of the floor of the anterior cranial fossa 

Part of the medial walls of the orbits 

Terminate medially at the anterior clinoid process (an anchoring site 

for the brain) 


Sphenoid Bone 

The pterygoid processes project inferior from the body. 

Function to anchor the pterygoid muscles that we use when we 

chew 

Openings in the sphenoid bone: 

Optic canals: connected by the optic chiasmatic groove. 

Allow the optic nerves to pass 

Superior orbital fissure: Allow the passage of cranial nerves 

III, IV, and VI which control eye movement 


Sphenoid Bone 

More openings in the sphenoid bone: 

Foramen rotundum: 

Branch of cranial nerve V for the maxillary nerve 

Foramen ovale: 

Branch of cranial nerve V for the mandibullar nerve 

Foramen spinosum: 

Transmits the middle meningreal artery that serves internal 

faces of some cranial bones 


Ethmoid Bone 


Figure 7.7

Ethmoid Bone 

Deepest of the skull bones; lies between the sphenoid and nasal 

bones 

Forms most of the bony area between the nasal cavity and the 

orbits 

The cribiform plates (seen from above) form the roof of the 

nasal cavities and the floor of the anterior cranial fossa 

The olfactory foramina: allow the olfactory nerves to pass 


Ethmoid Bone 

Crista galli: (triangular process) 

Attachment site for the dura mater (the 

outermost covering of the brain) 

Perpendicular plate 

Projects inferiorly in the median plane 

Forms the superior part of the nasal septum 

(which divides the nasal cavity right and left) 


Ethmoid Bone 

Right & left lateral masses: 

Riddled w/ ethmoid sinuses (acts as sieve) 

Superior/middle nasal conchae (turbinates) 

Protrude into the nasal cavity 

Orbital plate: 

Located on the lateral surfaces of the lateral masses 

Contribute to the medial walls of the orbits 


Wormian Bones 

Tiny irregularly shaped bones that appear within 

sutures 


Facial Bones 

14 bones (6 paired sets) of which only the mandible and 

vomer are unpaired 

The paired bones are: 

Maxillae 

Zygomatics 

Nasals 

Lacrimals 

Palatines 

inferior conchae 


Mandible and Its Markings 

The mandible (lower jawbone) is the largest, 

strongest bone of the face 

Its major markings include the coronoid process, 

mandibular condyle, the alveolar margin, and the 

mandibular and mental foramina 




Figure 7.8a


The mandible (lower jaw) is the largest, strongest bone of the 

face 

The body forms the chin 

The rami meet the body posteriorly at a mandibular angle 

The mandibular notch separates the coronoid and condyle 

processes or the rami 

The coronoid process (anterior) is the insertion point for the 

large temporalis muscle that elevates the lower jaw during 

chewing 



The mandibular condyle (posterior) articulates 

with the mandibular fossa of the temporal bone 

forming the temporomandibular joint 

Mandibular body anchors the teeth 

Alveolar margin: the superior border of the body 

contains the sockets win which the teeth are 

embedded 



Mandibular symphysis: 

Site of fusion of the two mandibular bones ( in infancy) 

Mandibular foramina 

Found on the medial surface of each ramus 

Nerve passage for tooth sensation (injection site for 

Lidocaine) 

Mental foramina: 

Lateral aspects of body 

Allow blood vessels and nerves to pass to skin of the 

chin 


Maxillary Bone 


Figure 7.8b

Maxillary Bones (maxillae) 

Medially fused bones that make up the upper jaw 

and the central portion of the facial skeleton 

Facial keystone bones that articulate with all other 

facial bones except the mandible 


Maxillary Bones: Major Markings 

Alveolar margins: 

Carry the upper teeth 

Anterior nasal spine: 

Site of fusion of maxillae (inferior to nose) 

Palatine processes: 

Project posteriorly from the alveolar margins 

Fuse medially forming the anterior 2/3 of the hard palate 

or bony roof of the mouth 



Incisive fossa (midline foramen) 

Posterior to teeth 

Passage for blood vessels/nerves 

Maxillary sinuses 

Largest of the paranasal sinuses 

Extend from the orbits to the roots of the upper teeth 



Zygomatic processes: 

Lateral articulation between the maxillae and zygomatic 

bones 

Inferior orbital fissure: 

Located deep within the orbit at the junction of the 

maxilla and the greater wings of the sphenoid 

Permits zygomatic nerve, maxillary nerve (cranial nerve 

V branch) and blood vessels to pass to the face 



Infraorbital foramen: 

Allows the infraorbital nerve (a continuation of 

the maxillary nerve) and artery to reach the face 


Zygomatic Bones 

Irregularly shaped bones (cheekbones) 

Articulate with the zygomatic processes of the 

temporal bones posteriorly, the zygomatic process 

of the frontal bone superiorly, and the zygomatic 

process of the maxillae anteriorly 

For part of the inferolateral 

Margins of the orbits 


Other Facial Bones 

Nasal bones 

Thin medially fused bones that form the bridge of the 

nose 

Articulate with the frontal bone superiorly, the maxillary 

bones laterally, and the perpendicular plate of the 

ethmoid bone posteriorly 

Cartilages form the “skeleton” of the external nose 

inferiorly 



Lacrimal bones: 

Contribute to the medial walls of the orbit 

Smallest and most fragile of the facial bones 

Articulate with the frontal bone superiorly, ethmoid bone 

posteriorly, and the maxillae anteriorly 

Contains a deep groove (lacrimal fossa) that houses the lacrimal 

sac that is part of the passage that allows tears to drain from the 

eye to the nasal cavity 



Palatine bones: 

Fashioned from 2 bony plates 

Horizontal: complete posterior portion of the hard palate 

Perpendicular: forms the posterior walls of the nasal 

cavity and the small parts of the orbits 

3 articulating processes: 

Pyramidal 

Sphenoidal 

orbital 



Vomer – plow-shaped bone that forms part of the 

nasal septum 

Inferior nasal conchae – paired, curved bones in 

the nasal cavity that form part of the lateral walls 

of the nasal cavity 


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Anterior Aspects of the Skull 

Parietal bone 

Frontal squama 

of frontal bone 

Nasal bone 

Sphenoid bone 

(greater wing) 

Temporal bone 

Ethmoid bone 

Lacrimal bone 

Zygomatic bone 

Infraorbital foramen 

Maxilla 

Mandible 

Mental 

foramen 

(a) 


Mandibular symphysis 

Frontal bone 

Glabella 

Frontonasal suture 

Supraorbital foramen 

(notch) 

Supraorbital margin 

Superior orbital 

fissure 

Optic canal 

Inferior orbital 

fissure 

Middle nasal concha 

Perpendicular plate 

Inferior nasal concha 

Vomer bone 

Ethmoid 

bone 

Figure 7.2a

Posterior Aspects of the Skull 

Lambdoid 

suture 

Sutural 

bone 

Occipital bone 

Superior nuchal line 

External 

occipital 

protuberance 

Occipitomastoid 

suture 

(b) 

External 

occipital 

crest 


Occipital 

condyle 

Sagittal suture 

Parietal bone 

Mastoid 

process 

Inferior 

nuchal 

line 

Figure 7.2b

External Lateral Aspects of the Skull 

Coronal suture Frontal bone 

Parietal bone 

Temporal bone 

Lambdoid 

suture 

Squamous suture 


Zygomatic process 

Occipitomastoid suture 

External acoustic meatus 

(a) 

Mastoid process 

Styloid process 

Mandibular condyle 

Mandibular notch 

Mandibular ramus 


Sphenoid bone 


Ethmoid bone 

Lacrimal bone 

Lacrimal fossa 

Nasal bone 


Maxilla 

Alveolar margins 

Mandible 

Mental foramen 

Mandibular angle Coronoid process 

Figure 7.3a

Midsagittal Lateral Aspects of the Skull 

Parietal bone 

Squamous 

suture 

Temporal 

bone 

Lambdoid suture 

Occipital 

bone 

Occipitomastoid 

suture 

External occipital 

protuberance 

(b) 

Internal acoustic 

meatus 

Sella turcica 

of sphenoid 

bone 

Pterygoid 

process of 

sphenoid 

Mandibular 

bone 

foramen 


Palatine 

bone 

Palatine 

process of 

maxilla 

Coronal suture 

Frontal bone 

Sphenoid bone 


Frontal sinus 

Crista galli 

Nasal bone 

Sphenoid sinus 

Ethmoid bone 

(perpendicular plate) 

Vomer bone 

Incisive fossa 

Maxilla 

Alveolar margins 

Mandible 

Figure 7.3b

Inferior Portion of the Skull 

Hard 

palate 

(a) 

Maxilla 

(palatine process) 


Temporal bone 

(zygomatic process) 

Vomer 

Mandibular 

fossa 

Styloid process 

Mastoid process 

Palatine bone 

(horizontal plate) 

Temporal bone 

(petrous part) 

Pharyngeal 

tubercle of 

basioccipital 

Parietal bone 

External occipital crest 

External occipital 

protuberance 


Foramen magnum 

Incisive fossa 

Medial palatine suture 

Infraorbital foramen 

Maxilla 

Sphenoid bone 


Foramen ovale 

Foramen 

lacerum 

Carotid canal 

External acoustic meatus 

Stylomastoid 

foramen 

Jugular foramen 

Occipital condyle 

Inferior nuchal line 

Superior nuchal line 

Figure 7.4a

Inferior Portion of the Skull 

Olfactory foramina 

Anterior cranial fossa 

Sphenoid 

(b) 

Lesser wing 

Greater wing 

Tuberculum sellae 

Hypophyseal fossa 

Sella Dorsum sellae 

turcica Posterior clinoid process 

Middle cranial 

fossa 

Temporal bone 

(petrous part) 

Internal 

acoustic meatus 

Posterior 

cranial fossa 

Parietal bone 


Foramen magnum 


(c) 

Frontal bone 

Cribriform plate 

Ethmoid 

Crista galli 

bone 

Optic canal 

Anterior clinoid process 

Foramen rotundum 

Foramen ovale 

Foramen spinosum 

Foramen lacerum 

Jugular foramen 

Hypoglossal canal 

Anterior 

cranial 

fossa 

Middle 

cranial 

fossa 

Posterior 

cranial 

fossa 

Figure 7.4b

The Axial Skeleton Eighty bones segregated into three regions

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