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© 2012 Pearson Education, Inc.

6 The Skeletal System:

Axial Division


Figure 6.1a The Axial Skeleton

SKELETAL SYSTEM

APPENDICULAR SKELETON

(see Figure 7.1)

AXIAL SKELETON 80

Skull and

associated

bones

Thoracic

cage

Vertebral

column

Skull

Associated

bones

Auditory

ossicles

Cranium

Face

Hyoid

Sternum

Ribs

Vertebrae

Sacrum

Coccyx

29

25

26

14

24

24

8

6

1

1

1

1

Anterior view of the skeleton

highlighting components of the

axial skeleton; the flowchart

indicates relationships among

the axial components.

126

206


Introduction

• The axial skeleton:

• Composed of bones

along the central axis

of the body

• Divided into three

regions:

• Skull

• Vertebral column

• Thoracic cage


Introduction

• Functional anatomy of the axial skeleton:

• Framework that supports and protects organs

in the dorsal and ventral body cavities

• Protects special sense organs for taste, smell,

hearing, balance, and vision

• Attachment sites for muscles that:

• Adjust the posture of the head, neck, and trunk

• Move the thoracic cage for respiration

• Stabilize the appendicular skeleton


Figure 6.2 Cranial and Facial Subdivisions of the Skull (Part 1 of 2)

SKULL

ASSOCIATED BONES

Hyoid bone 1

7

6

Auditory ossicles

enclosed in

temporal bones

(detailed in

Chapter 18)

FACE CRANIUM 14 8

2

2

2

2

2

2

1

1

2

1

2

1

1

Maxillae

Palatine bones

Nasal bones

Inferior nasal

conchae

Zygomatic bones

Lacrimal bones

Vomer

Mandible

Occipital bone

Parietal bones

Frontal bone

Temporal bones

Sphenoid

Ethmoid

1


Figure 6.2 Cranial and Facial Subdivisions of the Skull (Part 2 of 2)

Facial Bones Cranial Bones

Nasal bone

Zygomatic

bone

Maxilla

Lacrimal

bone

Vomer

Mandible

Frontal

bone

Sphenoid

Ethmoid

Parietal bone

Temporal

bone

Occipital

bone


• Lambdoid suture

• Suture between the occipital bone and the two parietal bones

(superior skull)

• Sagittal suture

• Suture between the two parietal bones

The Skull and Associated Bones


• Sagittal suture

• Between the two parietal bones

• Coronal suture

• Between the frontal bone and the two parietal bones



• Temporal bone

• Mastoid process

• External acoustic

meatus

• Zygomatic arch

• Styloid process

• Sphenoid bone

• Squamous suture



Figure 6.3d The Adult Skull (Part 1 of 2)

Anterior view of the bones of the adult skull

Parietal bone

Supra-orbital foramen

Sphenoid

Temporal bone

Ethmoid

Palatine bone

Lacrimal bone

Zygomatic bone

Nasal bone

Maxilla

Inferior nasal concha

Vomer

Mandible

Frontal bone

Coronal suture

Optic canal

Superior orbital fissure

Inferior orbital fissure

Infra-orbital foramen

Middle nasal concha

Perpendicular plate

of ethmoid

Mental foramen


Figure 6.3e The Adult Skull (Part 1 of 2)

Inferior view of the adult skull, mandible removed

Zygomatic bone

Vomer

Sphenoid

Foramen ovale

Styloid process

External

acoustic meatus

Jugular foramen

Occipital bone

Palatine process of maxilla

Maxilla

Foramen lacerum

Carotid canal

Temporal bone

Mastoid process

Occipital condyle

Foramen magnum

Palantine bone


Figure 6.4 Sectional Anatomy of the Skull, Part I (Part 1 of 2)

Frontal bone

Ethmoid

Sphenoid

Temporal bone

Carotid canal

Parietal bone

Occipital bone

Crista galli

Cribriform plate

Sella turcica

Foramen rotundum

Foramen lacerum

Foramen ovale

Foramen spinosum

Internal acoustic meatus

Jugular foramen

Hypoglossal canal

Foramen

magnum

Horizontal section


Figure 6.5 Sectional Anatomy of the Skull, Part I (Part 1 of 2)

Sagittal section

Sphenoid

Sphenoidal sinus (right)

Frontal sinus

Crista galli

Nasal bone

Perpendicular plate of ethmoid

Vomer

Hypophyseal fossa

of sella turcica


• The Occipital Bone

• Foramen magnum

• Opening for the spinal cord

• Occipital condyles

• Articulate with the first cervical vertebra

• Hypoglossal canals

• Opening for the hypoglossal nerve that innervates the tongue



• The Temporal Bone

• Relatively flat bone of

the skull

• Mastoid process

• Styloid process

• Neck muscle

attachment

• External acoustic

meatus

• Entrance into the ear

canal



• The Sphenoid Bone

• Sella turcica

• Hypophyseal fossa (fossa for the pituitary gland)

• Optic canals

• Openings for the optic nerves



• The Ethmoid Bone

• Perpendicular plate

of the ethmoid

• Crista galli

• Cribriform plate

• Cribriform plate

foramina (olfactory

foramina)

• Openings for the

olfactory nerves



• The Maxillae

• Make up the upper jaw

• Consists of a left and

right maxilla

• Maxillary sinuses

• Infra-orbital foramen

• Openings for the

maxillary nerve passing

through the foramen

rotundum



• The Mandible • Makes up the lower jaw

• Mandibular condyle • Articulates with the mandibular

fossa of the temporal bone

• Mandibular notch

• Coronoid process

• Ramus

• Angle

• Body • Mental foramina (openings

for the passage of nerves)

• Mental protuberance (bony ridge on the anterior edge) = prominent “chin”



• The Hyoid Bone • Slender, curved bone

located inferior to the skull

between the mandible and

the larynx (voice box).

• Does not articulate with any

other bone

• Serves as sites for

attachment for tongue and

larynx muscles and

ligaments.



• Auditory ossicles

• Three tiny ear bones

called auditory

ossicles are housed

within each temporal

bone.

• the malleus

• the incus

• the stapes



• The largest cavity is the

cranial cavity, which

encloses, cushions, and

supports the brain.

• The skull also has several

smaller cavities, including

the orbits (eye sockets),

the oral cavity (mouth),

the nasal cavity, and the

paranasal sinuses.

Cavities of The Skull


• Have a mucous lining

that helps to humidify

and warm inhaled air.

• Cause these skull

bones to be lighter.

• Provide resonance to

the voice.

Sinuses


• Major features of the

infant skull

• 4 major fontanel areas

• Membranous areas

where sutures will

eventually form

• Anterior fontanel

(baby’s “soft spot”)

• Posterior fontanel

• Sphenoidal fontanels

• Mastoid fontanels

The Skull of Infants


•Functional anatomy of the fontanels

• Allow flexibility of the skull bones during the

birthing process

• These membranous areas are actually the

dura mater of the brain, which is a thick

membranous material that helps to protect the

brain.

• You can feel the infant’s pulse in the area of

the anterior fontanel. Blood vessels lie deep to

the fontanel.

• They close by 15 months of age

The Skull of an Infant


The Vertebral Column

• The adult vertebral

column is made up of 26

bones:

• 24 vertebrae

• 7 cervical vertebrae

• 12 thoracic vertebrae

• 5 lumbar vertebrae

• 1 sacrum (5 fused

vertebrae)

• 1 coccyx (3 to 5 fused

vertebrae)



•Functional anatomy of the vertebral column

• Encloses and protects the spinal cord

• Supports the skull

• Supports the weight of the head, neck, and trunk

• Transfers weight to the lower limbs

• Helps maintain the upright position of the body


• There are 4 major curves

of the vertebral column

• Cervical curve

• Thoracic curve

• Lumbar curve

• Sacral curve

• These curves, along with

muscle attachment to the

various vertebral

processes, help to

maintain balance




• Abnormal curvatures of

the vertebral column

• Scoliosis

• Abnormal lateral curvature

• Kyphosis

• Exaggerated posterior

curvature of the thoracic

region

• Lordosis

• Exaggerated anterior

curvature of the lumbar

region

Scoliosis Kyphosis

“Hunchback”

Lordosis

“Swayback”



• Special features of the vertebrae

• Cervical number 1 is the atlas

• “nodding”

• Cervical number 2 is the axis

• The axis has a structure called the dens

• The atlas pivots on the dens of the axis, allows rotation of the head

• “shaking head”



• Vertebral Processes

(Cervical Vertebrae)

• Vertebral body

• Vertebral foramen

• Spinous process

• Transverse process

• Transverse foramen



• Vertebral Processes (Thoracic Vertebrae) - The ribs articulate with the 12 thoracic vertebrae • Vertebral body


• Spinous process




• Vertebral Processes (Lumbar Vertebrae)- support the weight of the torso • Vertebral body


• Spinous process



• Cervical: smallest, lightest; transverse foramen; vertebral foramen triangular; short spinous process

• Thoracic: costal facets (for ribs); heart-shaped body; vertebral foramen is oval/round; long spinous process

• Lumbar; blocklike body; blunt spinous process




• Sacrum and Coccyx • Sacral foramina

• Median sacral crest

• Lateral sacral crest

• Sacral hiatus


The Thoracic Cage

•The thoracic cage has two functions:

• It protects the heart, lungs, thymus, and other

structures within the cavity

• It serves as the attachment site for muscles

involved in:

• Respiration

• Positioning the vertebral column

• Movements of the pectoral girdle and upper limb


The Thoracic Cage

• The Thoracic Cage

• Sternum

• Manubrium

• Body

• Xiphoid

• Jugular notch


The Thoracic Cage

• The Thoracic Cage

• Ribs

• True ribs: 1–7

• False ribs: 8–12

*(floating ribs = 11–12)


The Thoracic Cage

•Rib Articulation

• Head

• Neck

• Tubercle of rib

• Body


Figure 6.27c The Thoracic Cage

A superior view of the articulation

between a thoracic vertebra and

the vertebral end of a left rib

Transverse

costal facet

Costal facet

Tubercle of rib

Neck

Angle

Head

(capitulum)

Vertebral

end

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