The Axial Skeleton
 The axial skeleton forms the longitudinal axis of the body, and can be
divided into 3 parts: the skull, the vertebral column, and the bony
thorax.
The Skull:
 Formed by two sets of bones:
o Cranium-encloses and protects brain tissue
o Facial bones-hold the eyes in position and allows facial
muscles to show expressions.
 All but one bone is joined by sutures (interlocking, immovable joints)
o Only the mandible is attached by a freely movable joint.
 The Cranium:
o Composed of 8 large, flat bones
o All but 2 (parietal and temporal) are single bones
o Frontal Bone: forms the forehead, eyebrow projections, and
superior part of orbit (eyesocket)
o Parietal Bones: paired and form most of the superior and lateral
walls
 Meet in the middle at the SAGITTAL SUTURE and form
the CORONAL SUTURE there they meet the frontal bone
o Temporal Bones: inferior to parietal bones
 Meet with pariteal bones at the SQUAMOUS SUTURE.
 There are important markings to note on the temporal
bones:
 External Auditory Meatus: leads eardrum to middle
ear
 Styloid Process: needlelike projection, inferior to the
external auditory meatus. Attachment point for
many neck muscles
 Zygomatic Process: a thin bridge of bone that joins
with the zygomatic bone (cheekbone)
 Mastoid Process: inferior and posterior to Ex. Aud
Meatus, and is full of mastoid sinuses. Also
attachment for neck muscles
 Jugular Foramen: junction of occipital and temporal
bones. Allows passage of jugular vein (drains
brain). Just anterior to it is the carotid canal through
which runs the carotid artery (supplies brain)
o Occipital Bone: the most posterior bone of the cranium
 Meets with the Parietal bones at the Lambdoid suture.
 In the base, is the Foramen Magnum (large hole) where it
surrounds the lower part of the brain and allows the spinal
cord to connect with the brain.
 Lateral (on the sides) to the Foramen magnum lie the
Occipital condyles which lie on the first vertebra of the
spinal column.
o Sphenoid Bone: butterfly shaped spans the width of the skull
and forms part of the floor of the cranium
 In its midline is the Sella Turcica (Turk’s saddle) which
holds the pituitary gland in place
 The Foramen Ovale, is a large opening in line with the
sella turcica that allows the passage of the cranial nerve
V to pass to the mandible muscles
 Sphenoid bones also forms the back of the orbits, and the
lateral part of the skull.
 In the interior of the skull, there are many air cavities
called the sphenoid sinuses.
o Ethmoid Bone: irregularly shaped and lies anterior to the
sphenoid.
 Forms the roof of the nasal cavity and part of the medial
walls of the orbits
 Projecting from its superior surface is the crista galli,
which is where the outermost projection of the brain
attaches.
 On each side the the crista are the cribriform plates (holey
areas) that allow fibers carrying impulses from the
olfactory (smell) receptors of the nose to reach the brain.
 Facial Bones:
o 14 bones make up the face (12 paired; mandible & vomer are
single)
o Maxillae: 2 maxillae or maxillary bones fuse to form upper jaw
 All facial bones, except the mandible, join to the maxillae
 Carry the upper teeth
 Projections are called Palatine processes, which form the
anterior part of the Palate.
 Also contain sinuses called Paranasal sinuses, which
drain into nasal passages
 They surround nasal passages, lighten skull bones,
and amplify the sounds we make when we speak.
 This is where sinusitis is common! Because it is
continuous with the nasal passages.
o Palatine Bones: lie posterior to palatine process of the Maxillae
(back end)
o Zygomatic Bones: cheekbones and a good portion of the lateral
walls of the orbits
o Lacrimal Bones: fingernail sized bones that form the medial
walls of each orbit. Has a groove to serve as a passage way
for tears (Spanish-lagrimas)
o Nasal Bones: small rectangular bones forming the bridge of the
nose (lower part is cartilage)
o Vomer Bone: single bone in the median line of the nasal cavity,
forming most of the septum.
o Inferior Conchae: thin curved bones projecting from the lateral
walls of the nasal cavity (superior and middle conchae are part
of the ethmoid bone)
o Mandible: lower jaw, and is the largest and strongest bone in
the face.
 Joins the temporal bones on each side, making the only
freely moving joints in the face.
 Carry lower teeth
o Hyoid Bone: Not considered part of skull, it is the only bone in
the body that is not connected directly to another bone.
 It is suspended in the midneck region about 2cm above
the larynx, where it is anchored to the styloid process
 Serves at a movable base for the tongue and attachment
point for neck muscles that influence the larynx (voicebox)
 Fetal Skull:
o The fetal skull is very large compared to the rest of its body.
 It is ¼ of the total body length, where in an adult it is 1/8.
o There are cartilaginous regions that have yet to be converted to
bone.
o Theses areas where the bones have not connected are called
fontanels (soft spots).
 The fontanels enabled compression during birth and allow
the baby’s brain to grow.
 Are gradually converted to bone by about 2 yrs of age.