1. The Axial Skeleton Forms longitudinal axis of the body 80 bones
40% of the bones in the human body

2. Axial Skeleton Three Regions: 1. Skull (8 cranial & 14 facial)
** bones associated with skull (6 auditory ossicles and hyoid)
2. Vertebral column (24 vertebrae, sacrum & coccyx)
3. Thoracic cage (sternum & 24 ribs)

3. Anatomy of the Cranium Eight cranial bones:
2 parietal
2 temporal
Frontal
Occipital
Sphenoid
Ethmoid
The cranial bones enclose the cranial cavity, a fluid-filled chamber that cushions and supports the brain
Cranial bones are thin and remarkably strong for their weight

4. Skull – Anterior View
Figure 7.2a

5. Frontal Bone
Forms the anterior portion of the cranium & the roof of the orbits (eye sockets)

6. Parietal Bones
Forms most of the superior and lateral aspects of the skull
Figure 7.3a

7. Occipital Bone
Located at the back and lower part of the cranium

8. Temporal Bones
Form part of both the lateral walls of the cranium & zygomatic arches
Figure 7.5

9. Parietal Bones & Major Associated Sutures
Four sutures mark the articulations of the parietal bones
1. Coronal suture – articulation between parietal bones and frontal bone anteriorly
2. Sagittal suture – where right and left parietal bones meet superiorly

10. Parietal Bones & Major Associated Sutures
3. Lambdoid suture – where parietal bones meet the occipital bone (posterior)
4. Squamosal or squamous suture – where parietal and temporal bones meet

11. Sphenoid Bone
Butterfly-shaped bone that forms part of the floor of the cranium, unites the cranial and facial bones, and acts as a cross brace that strengthens the sides of the skull
Forms the central wedge that articulates with all other cranial bones

12. Ethmoid Bone
Most deep of the skull bones; lies between the sphenoid and nasal bones
Figure 7.7

13. Facial Bones
Fourteen bones of which only the mandible and vomer are unpaired
The paired bones are the maxillae, zygomatics, nasals, lacrimals, palatines, and inferior conchae

14. Mandible
The mandible (lower jawbone) is the strongest bone of the face
Figure 7.8a

15. Maxillary Bones
Medially fused bones that make up the upper jaw and the central portion of the facial skeleton (largest facial bones)
Figure 7.8b

16. Zygomatic Bones
Irregularly shaped bones (cheekbones) that form the prominences of the cheeks and the inferolateral margins of the orbits

17. Other Facial Bones
Nasal bones – thin medially fused bones that form the bridge of the nose
Lacrimal bones – contribute to the medial walls of the orbit and contain a deep groove that house the tear ducts
Palatine bones – two bone plates that form portions of the hard palate and contribute to the floor of each orbit

18. Other Facial Bones continued…
Vomer – 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

19. Hyoid Bone Lies just inferior to the mandible in the anterior neck
Only bone of the body that does not articulate directly with another bone
Attachment point for neck muscles that raise and lower the larynx during swallowing and speech
Figure 7.12

20. Vertebral Column 26 irregular bones (vertebrae)
Provide a column of support, bearing the weight of the head, neck, and trunk.
Transfers weight to the appendicular skeleton of the lower limbs
Protects spinal cord
Helps maintain an upright body position
Approx. length of an adult column is 71cm

21. Vertebral Column Lumbar vertebrae 5 bones of the lower back
Cervical vertebrae
7 bones of the neck
Thoracic vertebrae
12 bones of the torso
Lumbar vertebrae
5 bones of the lower back
Figure 7.13

22. Vertebral Column Sacrum - 5 fused vertebrae
bone inferior to the lumbar
vertebrae that articulates with the hip bones
Coccyx – 4 fused vertebrae
Figure 7.13

23. Disks are small shock absorbers between the vertebrae (gel-like interior)

24. General Structure of Vertebrae:
Vertebral body (centrum) – disc-shaped, weight- bearing region
2. Vertebral arch – composed of pedicles (walls) and flat layers called laminae (roof)
** forms the posterior margin of each vertebral foramen (together they form the vertebral canal which encloses the spinal cord)
3. Articular processes– projections on each vertebra

25. Table 7.2

26. Cervical Vertebrae
Most mammals have 7 cervical vertebrae (giraffes, whales, mice & humans)
Seven vertebrae (C1- C7) are the smallest and lightest vertebrae

27. Cervical Vertebrae: The Atlas (C1)
Holds up the head
Has no body and no spinous process

28. Cervical Vertebrae: The Axis (C2)
The axis has a body, spine, and vertebral arches as do other cervical vertebrae
Articulates with the atlas to permit rotation
Figure 7.16c

29. Thoracic Vertebrae There are twelve vertebrae (T1-T12)
Distinctive heart-shaped body (more massive than that of a cervical vertebra)
Each thoracic vertebra articulate with ribs

30. Lumbar Vertebrae
The five lumbar vertebrae (L1-L5) are located in the small of the back and have an enhanced weight-bearing function
Largest vertebrae

31. Breakfast: 7 a. m. (7 cervical) Lunch: 12 p. m
Breakfast: 7 a.m. (7 cervical) Lunch: 12 p.m. (12 thoracic) Dinner: 5 p.m. (5 lumbar)
Tip: Mealtimes

32. Sacrum
Consists of five fused vertebrae (S1-S5), which shape the posterior wall of the pelvis
Begin fusing after puberty and are completely fused at age 25-30
Protects reproductive, digestive, and urinary organs
It articulates with L5 superiorly, and with the auricular surfaces of the hip bones

33. Coccyx Coccyx (Tailbone)
The coccyx is made up of four (in some cases three to five) fused vertebrae that articulate superiorly with the sacrum
Generally begun fusing by age 26

34. Sacrum and Coccyx
Figure 7.18b

35. Bony Thorax (Thoracic Cage)
The thoracic cage is composed of the thoracic vertebrae, the ribs, and the sternum
Functions
Forms a protective cage around the heart, lungs, and great blood vessels
Supports the shoulder girdles and upper limbs
Provides attachment for many neck, back, chest, and shoulder muscles

36. Figure 7.19a

37. Sternum (Breastbone)
A dagger-shaped, flat bone that lies in the anterior midline of the thorax
Fusion is not complete until at least age 25 (until this age the sternal body consist of four separate bones)

38. Ribs There are twelve pair of ribs
All ribs attach posteriorly to the thoracic vertebrae
The superior 7 pair (true, or vertebrosternal ribs) attach directly to the sternum via costal cartilages
Ribs 8-10 (false, or vertebrocondral ribs) attach indirectly to the sternum via costal cartilage
Ribs (floating, or vertebral ribs) have no anterior attachment