The axial skeleton comprises the skull, vertebral column, ribs, and sternum. The skull includes the cranial bones that enclose the brain (occipital, parietal, interparietal, temporal, frontal, sphenoid, ethmoid) and facial bones. The occipital bone forms the caudal part of the cranium and articulates with the atlas vertebra. The parietal bones form the roof of the cranium. The temporal bone forms part of the lateral skull and includes the squamous, tympanic, and petrous portions.

1. Axial skeleton:
The axial skeleton comprises the skull, vertebral
column, ribs and sternum.

3. Skull:
The skull includes all of the bones of the head.
The head consists of the cranium and face and
accordingly the bones are divided in to cranial
bones (enclose the brain), and facial bone
(forming the skeleton of oral and nasal cavities).

4. The cranial bones (encloses the brain)
include:
1- Occipital bone.
2- Parietal bone.
3- Interparietal bone.
4- Temporal bone.
5- Frontal bone.
6- Sphenoid bone.
7- Ethmoid bone.

6. 1- The occipital bone:
a- It is situated at the caudal part of the cranium.
b- Its lower part is perforated centrally by the foramen
magnum.
c- The lateral parts bear the occipital condyles, which
articulate with the atlas.
d- Lateral to the condyle is the jugular process.
e- Between the root of this process and the occipital condyle
is the condyloid fossa, in which there is the hypoglossal
foramen.

7. f- The basilar part is strong, which extends forward from
the ventral margin of the foramen magnum and fused with
the body of the sphenoid bone at basilar tubercles.
g- The external surface of the occipital bone is crossed by
the nuchal crest which joins the temporal crest laterally.
h- The external occipital protuberance is present on which
the ligamentum nuchae is attached.

8. 2- The parietal bone:
a- The two parietal bones form the greater part of the roof of
the cranium; they unite in the middle line called external
parietal crest (external sagittal crest).
b- Each parietal bone is quadrilateral in outline and has two
surfaces and four borders.
c- The external (parietal surface) is convex.
d- The internal (cerebral surface) is concave.

9. 3- The interparietal bone:
a- This bone is centrally placed between the two
parietal bones.
b- It is usually described as a single bone.
c- The caudal border joins the occipital bone.
d- The cranial and lateral borders are united with the
parietal bones.

10. 4- The temporal bone:
a- The temporal bone forms the greater part of the
lateral wall of the cranium.
b- It is situated between the occipital behind, the
parietal dorsally, the frontal in front and sphenoid
ventrally.
c- It consists of: squamous temporal bone, tympanic
temporal bone and petrous temporal bone.
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12. (The squamous temporal bone includes the following):
1- zygomatic process: it is connects with the zygomatic
bone to make the zygomatic arch.
2- mandibular fossa: this is form when the mandible
attaches to form the temporomandibular joint

13. (The tympanic temporal bone includes the following):
1- Tympanic bulla: it is large bulbus part on the ventral
side of the skull.
2- External acoustic meatus: it is bony canal for the ear.

14. (The petrous temporal bone):
1- Is placed between the occipital bone behind and
the parietal bone in front, it consists of mastoid
process.
2- The muscular process is a sharp spine which project
from the base of petrous temporal bone.

15. 5- The frontal bone:
a- the frontal bones are situated between the
parietal behind and the nasal bones in front.
b- Each is irregularly quadrilateral, and consists of
nasofrontal and orbital parts.

16. 6- The sphenoid bone:
a- The sphenoid bone is situated at the base of the cranium.
b- It consists of body, pair of wings and two pterygoid processes.
Wings of sphenoid bone:
1- They are irregularly quadrilateral in outline.
2- At the junction of wing with the body there is a small groove which
leads forward to the pterygoid canal.
Two Pterygoid processes:
1- Arise from the wings of the sphenoid bone.
2- Its root is perforated by the alar foramen.

18. 7- The ethmoid bone:
It lies in front of the body and the wings of the sphenoid bone, or
located between the eyes on the rostral side of the brain. This
includes the following:
a- Cribriform plate:
1- Is a shelf like partition between the cranial and nasal cavities.
2- Each half of the cribriform plate forms a deep oval cavity
(ethmoidal fossa) which lodges the olfactory bulb.
3- The plate is perforated by numerous small foramina for the passage
of the olfactory nerve filaments.--

19. a- Cribriform plate:
1- Is a shelf like partition between the
cranial and nasal cavities.
2- Each half of the cribriform plate
forms a deep oval cavity (ethmoidal
fossa) which lodges the olfactory bulb.
3- The plate is perforated by numerous
small foramina for the passage of the
olfactory nerve filaments.--

20. b- Perpendicular plate:
1- Is a median plate and forms the caudal part of the nasal
septum.
2- Its cranial border is continuous with the septal cartilage.
3- Its caudal border projects in to cranial cavity.
4- Its dorsal border joins the frontal bone.
5- And its ventral border is received in to the groove of the
vomar.
c- Ethmoid labyrinth: it is the scroll like located on the plate.