1. 7
The Axial Skeleton

2. An Introduction to the Skeletal system
206 bones in adult body
Divided into:
Axial skeleton: bones along the longitudinal axis of the body
Appendicular: bones of the limbs and bones that attach limbs to the axial skeleton

3. 7-1 The Axial Skeleton
The Axial Skeleton forms the longitudinal axis of the body
Has 80 bones
The skull
8 cranial bones
14 facial bones
Bones associated with the skull
6 auditory ossicles
The hyoid bone
The vertebral column
24 vertebrae (singular = vertebra)
The sacrum
The coccyx
The thoracic cage
24 ribs
The sternum

4. Figure 7-1a The Axial Skeleton
SKELETAL SYSTEM
206
APPENDICULAR SKELETON
AXIAL SKELETON 80
(see Figure 8–1) 8
Cranium
Skull 14
Face
Skull and
associated
bones
Auditory
ossicles 29 6
Associated
bones 1
Hyoid 1
Sternum
Thoracic
cage 25 24
Ribs 24
Vertebrae 1
Sacrum 26
Vertebral
column 1
Coccyx
An anterior view of the entire skeleton, with the axial components highlighted.
The numbers in the boxes indicate the number of bones in the adult skeleton. 4

5. 7-1 The Axial Skeleton Functions of the Axial Skeleton
Supports and protects organs in body cavities
Provides attachment for muscles that
Adjust movements of head, neck, and trunk
Perform respiratory movements
Stabilize or position parts of appendicular skeleton
Joints of axial skeleton are immovable or permit very little movement

6. Figure 7-2 Cranial and Facial Subdivisions of the Skull
FACE 14
CRANIUM 8
ASSOCIATED BONES 7
Maxillary bones 2
Occipital bone 1
Palatine bones 2
Parietal bones 2
Hyoid bone 1
Auditory ossicles
enclosed in
temporal bones
(detailed in
Chapter 17)
Nasal bones 2
Frontal bone 1 6
Inferior nasal
conchae 2
Temporal bones 2
Sphenoid 1
Zygomatic bones 2
Ethmoid 1
Lacrimal bones 2
Vomer 1
Mandible 1 6

7. 7-3 The Cranial Bones of the Skull
The Cranial Bones (all flat bones except sphenoid and ethmoid)
Occipital bone
Parietal bones
Frontal bone
Temporal bones
Sphenoid
Ethmoid

8. Figure 7-2 Cranial and Facial Subdivisions of the Skull
The calvaria (skullcap) consists of
1 X Occipital bone
2 X Parietal bones
1 X Frontal bone
FRONTAL
BONE
PARIETAL BONE
SPHENOID
TEMPORAL
BONE
ETHMOID
OCCIPITAL
BONE
Cranial bones
Facial bones 8

9. Figure 7-6a The Frontal Bone
Supra-orbital
foramen
Anterior surface 9

10. Figure 7-6b The Frontal Bone
Supra-orbital
foramen
Frontal
sinus
Inferior (orbital) surface 10

11. Supraorbital margins: thickened margin above the orbits, protects eye.
The Frontal Bone forms the anterior part of the cranium (Forehead) and the roof of the orbits (eye sockets)
Frontal bone originated from two bones at birth that completely fuse by age 6-8
Landmarks Include
Supraorbital foramen: opening just above the orbits for blood vessels/sensory nerve.
Supraorbital margins: thickened margin above the orbits, protects eye.
Frontal sinuses: spaces that open into nasal cavity.

12. The Two Parietal Bones form part of the superior and lateral surfaces of the cranium
Right parietal bone, lateral view

13. Figure 7-7b The Temporal Bones
Mandibular
fossa
External
acoustic meatus
Zygomatic
process
Styloid process
Mastoid process
Lateral view of the
right temporal bone 13

14. Two temporal bones- Form inferior and lateral wall of the cranium
Landmarks Include
Zygomatic process: Articulates with temporal process of zygomatic bone to form the zygomatic arch
Mandibular fossa: Articulates with the mandibular condyle of mandible forming the temporo-mandibular joint (TMJ)
Mastoid process: For neck muscle attachment
Styloid process: To attach tendons and ligaments of the hyoid, tongue, and pharynx
External acoustic (or auditory) meatus (canal): ends at tympanic membrane: allows sound waves to vibrate the eardrum

15. Figure 7-5a The Occipital and Parietal Bones
condyle
Foramen
magnum
External occipital
protuberance
Occipital bone, inferior view 15

16. Occipital bone forms posterior wall.
Landmarks Include
Foramen magnum -large opening for the spinal cord to exit the cranium.
Occipital condyles-rounded surfaces on lateral sides of foramen magnum, to articulate with C1.
External occipital protuberance- bony projection on midline of inferior surface for the attachment of neck and cervical ligaments.
attachment site for ligaments
Occipital condyles articulate with 1st cervical vertebra (C1) forming the atlanto-occipital joint
Inferior and superior nuchal lines: attachment site of muscles and ligaments
Foramen magnum connects cranial and spinal cavities: opening for spinal cord

17. Anterior surface Superior Sphenoidal orbital fissure sinus Orbital
Figure 7-8b The Sphenoid
Superior
orbital fissure
Sphenoidal
sinus
Orbital
surface
Body
Anterior surface 17

18. Superior surface Lesser wing Greater wing Sella turcica
Figure 7-8a The Sphenoid
Lesser
wing
Greater wing
Sella turcica
Superior surface 18

19. The Sphenoid
Appearance of a butterfly; found in the middle of the skull; forms part of the cranial floor;
referred to as the “keystone” – articulates will all other cranial bones; forms the posterior and lateral walls of the orbit; when viewed anteriorly.
Landmarks Include
Sella turcica: “turkish saddle” on superior surface to accommodate pituitary gland).

20. Superior surface Lateral mass containing ethmoidal labyrinth
Figure 7-9a The Ethmoid
Lateral mass
containing
ethmoidal
labyrinth
Cribriform
plate
Crista galli
Perpendicular
plate
Superior surface 20

21. Posterior surface Crista galli Superior nasal concha Perpendicular
Figure 7-9b The Ethmoid
Crista galli
Superior
nasal
concha
Perpendicular
plate
Middle nasal
concha
Posterior surface 21

22. The Ethmoid: Sponge-like bone that forms roof of the nasal cavity, part of the nasal septum and medial orbital wall
Markings Include
The Cribriform Plate: Forms floor of the cranium and roof of the nasal cavity
Crista galli: bony projection upward from cribriform plate that attaches to the the brain.
Perpendicular plate: vertical plate that forms part of the nasal septum
Superior and middle nasal conchae: bony projections that protrude into nasal cavity, increase surface area for warming, filtering and humidifying of incoming air
Ethmoid sinuses: composed by several ethmoidal cells.

23. 7-3 The Facial Bones of the Skull
The Facial Bones (irregular bones)
Maxillae (maxillary bones)
Palatine bones
Nasal bones
Vomer
Inferior nasal conchae
Zygomatic bones
Lacrimal bones
Mandible

24. Figure 7-10a The Maxillae and Palatine Bones
Infra-orbital
foramen
Alveolar
process
Alveoli
An anterolateral view of the
right maxilla. 24

26. Maxillae: Form the upper jawbone, forms the floor of the orbits and nasal cavity; forms part of the hard palate
(two bones that fuse before birth)
Landmarks include:
Infraorbital foramen: openings for nerve and blood vessels just inferior to the orbits.
Alveoli: sockets in which teeth are embedded
Palatine process: horizontal part of the maxilla that forms the anterior part of the hard palate (roof of the oral cavity)
Developmental abnormalities
Cleft lip: split upper lip
Cleft palate: failure of bones to fuse at midline

27. An anterior view of the two
palatine bones.
Orbital process 27

28. The two Palatine Bones:
Form the posterior one-third of hard palate (maxilla making up the anterior 2/3).
Make up a small portion of the floor of orbits

29. Figure 7-11 The Smaller Bones of the Face
Supra-orbital foramen
NASAL BONE
SPHENOID
TEMPORAL BONE
ZYGOMATIC BONE
Infra-orbital foramen
MAXILLA
Perpendicular plate
of ethmoid
VOMER
Bony nasal septum 29

30. The two Nasal Bones
Support the bridge of the nose
Connect to cartilages of the distal part of the nose

31. The Vomer
Forms inferior and slightly posterior portion of the nasal septum.
Articulates with the perpendicular plate of the ethmoid to form the nasal septum.
Deviated Nasal Septum:
Too much deviation from developmental abnormalities or injuries affect breathing, sinus drainage and may cause snoring
Can be surgically repaired

32. Figure 7-11 The Smaller Bones of the Face
Lacrimal sulcus
Superior orbital
fissure
LACRIMAL BONE
Middle nasal
concha
INFERIOR NASAL CONCHA
Temporal process of
zygomatic bone
Mastoid process
Perpendicular plate
of ethmoid
VOMER
Bony nasal septum 32

33. The two Inferior Nasal Conchae
The largest of the three nasal conchae (superior and middle nasal conchae are part of ethmoid)
Create air turbulence in the nasal cavity
Increase the epithelial surface area
Warm and humidify inhaled air

34. The two Lacrimal Bones form part of the medial wall of the orbital cavity
The smallest facial bones
Landmarks include:
Lacrimal fossa
Lacrimal foramen: located in the fossa, a hole through which the tear duct passes to drain tears into nasal cavity

36. The Zygomatic Bones (cheekbones)
Contribute to the rim and lateral wall of the orbit
Form part of the zygomatic arch
Landmarks include:
Temporal process: Meets the zygomatic process of the temporal bone forming the zygomatic arch

37. Figure 7-12a The Mandible and Hyoid Bone
Articular surface for
temporomandibular
joint
Coronoid process
Teeth
Alveolar process
Head
Ramus
Body
Mental
protuberance
Condylar process
Mental foramen
Angle
A lateral and slightly superior
view of the mandible 37

38. Mandible
The lower jaw bone; strongest and the only movable bone among the facial bones.
Landmarks include:
Body: main portion of the mandible, curved horizontal portion; Ramus: the arm of the mandible, vertical portion
Condylar process: rounded knob projection that articulates at the mandibular fossa of the temporal bone--forms temporomandibular joint - TMJ.
Coronoid process: projection for the temporalis muscle, used in chewing.
Mandibular foramen: entrance to mandibular canal, a passageway for nerves and blood vessels that service lower teeth.
Mental foramen: passage for nerve/blood vessels from chin.
Alveoli: sockets in which teeth are embedded.

39. Figure 7-12b The Mandible and Hyoid Bone
Alveolar
process
Condylar process
Coronoid process
Mandibular foramen
A medial view of the right mandible 39

40. Axial Skeletal System – Orbital cavity bones
Formed by 7 bones:
Frontal, Sphenoid, Ethmoid, Zygomatic, Maxillae, Lacrimal,Palatine 40

41. Paranasal sinuses
Air-filled cavities of bones surrounding the nasal cavity
Lined with mucous membranes
Protect the entrances of the respiratory system
Decrease the weight of the skull
Give resonance and amplification to voice
Located in frontal, maxillary, ethmoid and sphenoid bones
Sinusitis: inflammation of the mucous membranes of the paranasal cavities

42. Frontal sinus Ethmoid sinus Sphenoidal sinus Maxillary sinus
Paranasal sinuses
Frontal sinus
Ethmoid sinus
Sphenoidal sinus
Maxillary sinus
(a) Anterior view

43. 7-5 Fontanelles
ation.aspx?gcid=000112&ptid=17
The Infant Skull
Grows rapidly
Is large compared to the body
Has many ossification centers

44. Fontanelles are non-ossified areas between cranial bones of the infant skull
Intramembranous ossification not yet completed.
Composed of fibrous connective tissue (soft spots)
Will eventually ossify to form sutures (~ 24 months after birth).
Provide flexibility for fetal head as it goes through the birth canal.
Allows for growth of brain.
Anterior fontanelle: largest of the fontanelles

45. Figure 7-15b The Skull of an Infant45

46. Sutures are the immovable joints of the skull-made of fibrous connective tissue
Coronal Suture: between frontal bone and parietal bones
Lambdoid Suture: between occipital and parietal bones
Sagittal Suture: between the two parietal bones
Squamous Suture: between temporal bones and parietal bones

47. Figure 7-3b The Adult Skull
OCCIPITAL BONE
Lambdoid
suture
PARIETAL
BONE
(right)
PARIETAL
BONE
(left)
Sagittal
suture
Coronal
suture
FRONTAL BONE
ZYGOMATIC
BONE
NASAL BONES
Superior view 47

48. The Hyoid Bone
Found in the anterior cervical region--inferior to the mandible.
U-shaped bone that supports the larynx
Connected to muscles involved in chewing and swallowing
Sign of strangulation if fractured
Only bone that does not connect with any other bone
Suspended to styloid process of temporal bone by ligaments and muscles

49. Figure 7-12c The Mandible and Hyoid Bone
An anterior view of the hyoid bone 49

50. 7-6 The Vertebral Column https://www.youtube.com/watch?v=1pWne6e1kfM
The Vertebral Column (Spine)
Protects the spinal cord
Supports the head and body
26 irregular bones in the adult (33 in newborn).
24 vertebrae, the sacrum, and the coccyx (tailbone)

51. Figure 7-16 The Vertebral Column
Vertebral Regions
Regions are defined
by anatomical
characteristics of
individual vertebrae.
Cervical
(7 vertebrae)
Thoracic
(12 vertebrae)
Lumbar
(5 vertebrae)
Sacral
Coccygeal 51

52. Four Spinal Curves Cervical curve Thoracic curve Lumbar curve
Sacral curve

53. *Newborn has a single curve
Thoracic and Sacral Curves
Are called primary curves (present during fetal development)
Or accommodation curves (accommodate internal organs)
Lumbar and Cervical Curves
Are called secondary curves (appear after birth)
Or compensation curves (shift body weight for upright posture)

54. Figure 7-16 The Vertebral Column
Spinal Curves
Vertebral Regions
Primary curves develop
before birth, and secondary
curves after birth.
Regions are defined
by anatomical
characteristics of
individual vertebrae.
The cervical curve, a
secondary curve, develops as
the infant learns to balance the
weight of the head on the
vertebrae of the neck.
Cervical
(7 vertebrae)
The thoracic curve, a
primary curve,
accommodates the
thoracic organs.
Thoracic
(12 vertebrae)
The lumbar curve, a
secondary curve, balances
the weight of the trunk over
the lower limbs; it develops
with the ability to stand.
Lumbar
(5 vertebrae)
The sacral curve, a
primary curve,
accommodates the
abdominopelvic organs.
Sacral
Coccygeal 54

55. Abnormal spinal curvatures.
Scoliosis
Kyphosis
Lordosis

56. Figure 7-18a Vertebral Anatomy
spinous process
Articular processes
transverse process
lamina
Vertebral foramen
Vertebral arch
pedicle
Vertebral body
The major components of
a typical vertebra 56

57. Vertebral Anatomy :
Body: thick, anterior disc shaped bony structure where the intervertebral discs sit, supports most of the weight.
Vertebral arch
Pedicles: bony bridges projecting laterally and posteriorly from the body.
Laminae: further extensions of the pedicles that fuse posteriorly.
Failure of laminae to fuse results in spina bifida, commonly associated with developmental abnormalities of the brain and the spinal cord- paralysis
Vertebral foramen: opening formed by the fusion of the pedicles and lamina;

58. Vertebral Anatomy :
Processes
Spinous process: formed by fusion of the laminae, project posteriorly, for the attachment of muscles.
Transverse processes: lateral projections from the junction of the pedicles and laminae; attachment of muscles or ribs.
Superior and inferior articular facets: flat surfaces on the upper and lower surfaces for articulation with vertebra just above or just below.

59. Intervertebral discs.
Functions:
Allow for a strong joint between the vertebrae.
Allows for flexibility.
To absorb shock.
With aging, the disc become stiff and compressed.
Results in decreased height and loss of flexibility

60. Figure 7-18e Vertebral Anatomy
Superior articular facets
Lamina of
vertebral arch
Intervertebral
foramen
Intervertebral
disc
Spinous process
Intervertebral
disc
Transverse process
Vertebral body
Inferior
articular
facet
Arrow passing
through vertebral
canal
A lateral and sectional view
of three articulated
vertebrae 60

61. The Cervical Vertebrae (7): C1-C7
Typical cervical vertebra:
Small vertebra; small centrum/body.
Bifid spinous process: splits at end.
Transverse foramina – a pair of holes close to the transverse processes for the passage of vertebral arteries, veins and nerves.

62. causes damage to spinal cord in whiplash injury
C1:Atlas:
Looks like a ring, no true body or spinous process.
Superior articular facets articulate with the occipital condyles of occipital bone (atlanto-occipital joint)- allows nodding of head.
Supports weight of the skull.
C2:Axis:
Has a tooth like projection at the body - dens or odontoid process - forms a pivot point with C1 - allows for the rotation of the head.
In children, fusion of C1 and C2 is incomplete: impact or severe shaking can cause dislocation of the dens and severe damage to spinal cord
causes damage to spinal cord in whiplash injury

63. C7 known as vetebra prominens
The last vertebra of one region generally resembles the first vertebra of the next
Long slender spinous process not bifid, forms the bump on the lower back of neck
Ligament extends from external occipital protuberance to C7

64. Cervical (neck) vertebrae:64

65. Thoracic Vertebrae (T1–T12)
Larger than cervical vertebrae
Rounded vertebral foramen
Long, sharp, inferiorly directed spinous processes
Body and transverse processes have facets for the articulation of ribs:
Costal facet on body: articulate with head of ribs
Transverse costal facet on transverse process: articulate with tubercle of ribs

66. Thoracic vertebrae: 66

67. Lumbar Vertebrae (L1–L5)
Largest of the vertebrae--support large amounts of body weight
Bodies large and oval shaped
Blunt, squarish and posteriorly directed spinous process

68. Lumbar vertebrae: 68

69. Table 7-2 Regional Differences in Vertebral Structure and Function (Part 2 of 2)69

70. Table 7-2 Regional Differences in Vertebral Structure and Function (Part 1 of 2)70

71. SACRUM AND COCCYX 71

72. Sacrum:
Fused 5 sacral vertebrae - completed by early 30’s.
Landmarks include:
Transverse lines: (sites where vertebrae fused)
Sacral canal: continuation of vertebral canal.
Sacral hiatus: inferior opening of the sacral canal.
Coccyx:
Commonly called the “tailbone”.
Fused 4 coccygeal vertebrae - fusion occurs around years of age.

73. 7-8 The Thoracic Cage The Thoracic Cage
Provides bony support to the walls of the thoracic cavity
Consists of:
Bodies of thoracic vertebrae
Ribs
Sternum (breastbone)
The Rib Cage: ribs and sternum together; important in respiration

74. Functions of the Thoracic Cage
Protects organs of the thoracic cavity
Heart, lungs, and thymus
Attaches muscles
For respiration
For maintenance of position of the vertebral column
For movements of the pectoral girdle and the upper limbs

75. Ribs (Costae) Are 12 pairs of long, curved, flat bones
Extend from the thoracic vertebrae
Intercostal spaces: spaces between the ribs that are occupied by intercostal muscles
Posteriorly: attach to the thoracic vertebrae.
Head of rib to the facet on the BODY of thoracic vertebrae
Tubercle of the rib to the facet on the transverse processes of thoracic vertebrae

76. 76

77. Ribs (Costae)
Anteriorly: Sternal end of only some ribs are attached to sternum.
True ribs (vertebrosternal ribs): ribs 1-7, connected to sternum by separate costal cartilages
False ribs: ribs 8-12, attach indirectly or not at all to sternum
Ribs 8-10 (vertebrochondral ribs) attach to sternum indirectly; their costal cartilage fuses together and attaches to the costal cartilage of ribs 7
Ribs are floating ribs because do not attach to sternum; anterior end is free

78. Figure 7-23a The Thoracic Cage78

79. The Sternum (Breastbone) is a flat bone
Found in the midline of the thoracic wall
Contains spongy bone with red bone marrow, common source of bone marrow biopsy

80. Figure 7-23a The Thoracic Cage
Jugular notch T1
Clavicular articulation 1
Manubrium 2 3
Sternum
Body
True ribs
(ribs 1–7) 4
Xiphoid
process 5
Costal
cartilages 10
T11 6
T12 11 7
Vertebrochondral
ribs
(ribs 8–10) 12 8 9
False ribs
(ribs 8–12)
Floating ribs
(ribs 11–12)
An anterior view, showing the
costal cartilages and the sternum 80

81. Three parts of the sternum
The manubrium- articulates with clavicle & cartilages of first rib pair
The sternal body-attaches directly to costal cartilages of ribs 2–7; indirectly to ribs 8-10
The xiphoid process-Does not articulate with the ribs
Occifies last-hyaline cartilage that does not ossifies until late aduthood
Attaches to diaphragm and rectus abdominis muscles
Palpable landmark for CPR
Often fractured during improper CPR