The Axial Skeleton
Forms longitudinal axis of the
body
 80 bones
 40% of the bones in the
human body

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)
Anatomy of the Cranium
Eight cranial bones:
1.
2.
3.
4.
5.
6.


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
Skull – Anterior View
Figure 7.2a
Frontal Bone

Forms the anterior
portion of the cranium &
the roof of the orbits (eye
sockets)
Parietal Bones

Forms most of the superior and lateral
aspects of the skull
Figure 7.3a
Occipital Bone

Located at the
back and lower
part of the cranium
Temporal Bones
Form part of both
the lateral walls
of the cranium &
zygomatic
arches
Figure 7.5
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
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
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

Ethmoid Bone

Most deep of the skull bones; lies between
the sphenoid and nasal bones
Figure 7.7
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
Mandible
The mandible
(lower jawbone)
is the strongest
bone of the face
Figure 7.8a
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
Zygomatic Bones

Irregularly shaped bones (cheekbones)
that form the prominences of the cheeks
and the inferolateral margins of the orbits
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
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
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
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
Vertebral Column
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
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
Disks are small shock absorbers
between the vertebrae (gel-like
interior)
General Structure of Vertebrae:
1.
Vertebral body (centrum) – disc-shaped, weightbearing 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
Table 7.2
Cervical Vertebrae

Most mammals have
7 cervical vertebrae
(giraffes, whales,
mice & humans)

Seven vertebrae (C1C7) are the smallest
and lightest
vertebrae
Cervical Vertebrae: The Atlas (C1)
◦ Holds up the head
◦ Has no body and no spinous process
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
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
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

Breakfast: 7 a.m. (7 cervical)
Lunch: 12 p.m. (12 thoracic)
Dinner: 5 p.m. (5 lumbar)
Tip: Mealtimes
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
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
Sacrum and Coccyx
Figure 7.18b
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
Figure 7.19a
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)
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 11-12 (floating, or vertebral ribs) have no
anterior attachment