Axial Skeleton
Cranium
Axial skeleton
• Major Divisions in the
skeletal system:
– Axial: Bones along the
center axis (medial) of
the body.
• Skull, Vertebral column,
rib cage
The Skull
• The skull is formed by two sets of bones:
1. The cranium encloses and protects the fragile
brain tissue ( 8 cranial bones: Frontal bone, 2
parietal bones, 2 temporal bones, the occipital
bone, the spenoid bone, ethmoid bone)
2. The facial bones hold the eyes in an anterior
position (14 facial bones: 2 nasal bones, 2
maxillae, 2 zygomatic bones, the mandible, 2
lacrimal bones, 2 palatine bones, 2 inferior nasal
conchae, vomer)
• All but one of the bones of the skull are joined
together by sutures, which are interlocking,
immovable joints
Frontal Bone
• Frontal Bone: Forms
the forehead, the
bony projections
under the eyebrows,
and the superior part
of each eye orbit
Parietal Bones
• The paired parietal
bones form most of the
superior and lateral
walls of the cranium
• They meet in the
midline of the skull at
the sagittal (front to
back) suture, and form
the coronal (up and
down) suture where
they meet the frontal
bone
Temporal Bones
• The temporal bones
lie inferior to the
parietal bones
• The temporal bones
and parietal bones
are joined at the
squamous
(sideways) sutures
Occipital Bone
• It is the most posterior
bone of the cranium
• It forms the floor and
back wall of the skull
• The occipital bone joins
the paretial bones
anteriorly at the
lambdoidal (along the
back) suture
Sphenoid Bone
• The butterflyshaped bone
spans the width of
the skull and
forms part of the
floor of the cranial
cavity
Ethmoid Bone
• The ethmoid bone is
very irregularly
shaped and lies
anterior to the
sphenoid
• It forms the roof of
the nasal cavity and
part of the medial
wall of the orbits(eye
sockets)
Parietal
Frontal
Coronal suture
Squamous
suture
Sphenoid
Lambdoidal suture
Ethmoid
Occipital
Temperal
Bone Surface Markings
• Bones have characteristic surface markings
– Structural features adapted for specific functions
• There are two major types of surface markings:
– 1) Depressions and openings
• Allow the passage of blood vessels and nerves or form
joints
– 2) Processes
• Projections or outgrowths that form joints or serve as
attachment points for ligaments and tendons
Temporal Bones Markings
• External auditory
meatus: a canal that
leads to the eardrum
and the middle ear
• Styloid process: a
sharp needle
projection. Many
neck muscles use the
styloid process as an
attachment point
Temporal Bones Markings
• Zygomatic process: a
thin bridge of bone
that joins with the
cheek bone
• Mastoid process: a
rough projection
posterior and inferior
to the external
auditory meatus,
which is full of air
cavities
Temporal Bones Markings
• Jugular foramen
(hole): the junction
of the occipital and
temporal bones,
allows passage of
the large jugular
vein which drains
the brain
• Just anterior to it is
the carotid canal
through which the
carotid artery runs,
supplying blood to
most of the brain
Occipital Bone Markings
• Foramen magnum
(large hole):
surrounds the
lower part of the
brain and allows
the spinal cord to
connect with the
brain
Sphenoid Bone Markings
• Sella turcica:
holds the
pituitary gland
in place
Facial Bone
• 2 Maxillae or
maxillary bones, fuse
to form the upper
jaw
• All facial bones
except the mandible
join the maxillae,
thus they are the
main or keystone
bones of the face
• The maxillae contains
sinuses, which drain
into the nasal
passages: Paranasal
sinuses
Palatine Bones
• The paired palatine
bone are posterior
to the palatine
processes of the
maxillae
• Failure of these
results in cleft
palate
Facial Bones
• Zygomatic bones:
Are commonly
referred to as the
cheekbones
• Lacrimal Bones:
fingernail size bones
forming part of the
medial wall to each
orbit (eye socket)
Facial Bones
• Nasal Bones: The
small rectangular
bones forming the
bridge of the nose
(the lower part of the
nose is made up of
cartilage)
• Vomer Bone: The
single bone in the
median line of the
nasal cavity
Facial Bones
• Inferior conchae:
Thin curved bones
projecting form the
lateral walls of the
nasal cavity
• Mandible: The lower
jaw. The largest and
strongest bone of the
face
The Hyoid Bone
• Lies inferior to the
mandible
• It is the only bone with
no direct articulation
with any other bone
• Acts as a movable base
for the tongue