Please answer the bell work question of the day. Than
you!
1. Differentiate Intramembranous
Ossification from Endochondral Ossification
Essentials of Anatomy and Physiology
Chapter 6:The Skeletal
System
The AXIAL SKELETON
The Axial Skeleton can be divided into 3 parts:
 the skull
 the vertebral column
 the bony thorax
THE SKULL:
1) CRANIUM – enclose and protect the fragile
brain tissue
2) FACIAL BONES – present the eyes in an
anterior position and form the base of the
facial muscles,which makes it possiblefor
us topresent our feelings to the world.
•SUTURES – interlocking joint that joins all but one of the
bones
•The mandible and the lower jaw bone, is attached to the
rest of the skull by a freely movable joint
Bones of the Skull and its important bone markings:
THE CRANIUM
•8 bones construct the cranium
•With the exceptions of two paired bones : parietal
and temporals ,all are single bones.
•Sometimes the six ossicles of the middle ear are
also considered part of the cranium but because the
ossicles are part of the hearing apparatus, it is
considered more part of the Special Sense.
The FRONTAL BONE
anterior portion of the cranium; forms
part of the forehead ,superior part of
the orbit and the floor of the anterior
cranial fossa
 Landmarks:
1. Supraorbital foramen ( notch) –
opening above each orbit allowing
blood vessels and nerves to pass.
2. Glabella- smooth area between the
eyes
The PARIETAL BONE
posterolateral to the frontal bone; forming
sides of the cranium
Landmarks:
1.Sagittal suture- midline articulation point of
the two parietal bones
2. Coronal Suture- point of articulation of
parietals with the frontal bone
The TEMPORAL BONE
Located below the parietal bones and contributing to the
sides of the cranium
 Landmarks:
1. Squamous sutures- point of articulation of the
temporal bone with the parietal bone
2. External acoustic canal- canal leading to the eardrum
and the middle ear
3. Mandibular fossa- the point where the mandible (
lower jaw) joins the cranium
4. Mastoid process- rough projection inferior and
posterior to external acoustic meatus; attachment sites for
muscles
5. Styloid process- attachment point for muscles and
ligaments for the neck.
•The mastoid process, full of air cavities and so
close to the middle air- a trouble spot for
infections- often becomes infected too, a
condition referred to as MASTOIDITIS.
Because the mastoid area is separated from the
brain by only thin layer of bone, an ear infection
that has spread to the mastoid process can
inflame the brain coverings or meninges .The
condition called MENINGITIS
The OCCIPITAL BONE
most posterior bone of the cranium- forms floor
and back wall. Joins the sphenoid bone anteriorly via
its occipital region
Landmarks:
1. Lambdoid sutures- site of articulation of the
occipital bone and parietal bone
2. Foramen Magnum- large opening in the base of
the occipital, which allows the spinal cord to join
with the brain.
3. Occipital condyles- round projection lateral to
the foramen magnum that articulates with the first
cervical vertebrae ( atlas)

The Sphenoid Bone
Bat-shaped bone forming the anterior plateau
of the middle cranial fossa across the width of
the skull.
The sphenoid bone is the keystone of the
cranium because it articulates with all the
cranial bones.
Landmark:
1. Sella Turnica- central depression, a
saddle-shaped region in the sphenoid midline. It
encloses the pituitary gland.

The ETHMOID BONE
 Irregularly shaped bone anterior to the sphenoid bone. Forms roof
of the nasal cavity, upper nasal septum, and part of the medial orbit
walls
Landmarks:
1. Crista Galli ( cock’s comb) – vertical projection providing a
point of attachment for the dura mater ,helping to secure the brain
within the skull
2. Cribriform plates- bent plates lateral to the crista galli
through which olfactory fibers pass to the brain from the nasal
mucosa.
3. Superior and middle nasal conchae ( turbinates)- the
conchae make air flow through the nasal cavity more efficient and
greatly increase the surface area of the mucosa that covers them, thus
increasing the mucosa’s ability to warm and humidify incoming air.
 14 bones composing the face, 12paired, only
the mandible and vomer are single bones.
 Hyoid bone, an additional bone, although
not a facial bone but it is considered because of
its location.
The MANDIBLE
the lower jawbone, which articulates with the
temporal bones in the only freely movable joints
of the skull
 Landmarks:
1. Mandibular body- horizontal portion,
forms the chin
2. Mandibular Ramus- vertical extensionof
the body on either side
3. Coronoid Process- jutting anterior portion
of the ramus; site of muscle attachment

The Maxillae or Maxillary Bone
two bones fused in the median suture; form the
upper jawbone and part of the orbits . All facial
bones, except the mandible,join the maxillae, thus
they are the main or keystone bones of the face.
Landmark:
1. Alveolar Margin- the inferior margin
containing sockets in which the teeth lie.

The LACRIMAL BONE
fingernail sized bones forming a part of the
medial orbit walls because the maxilla and
the ethmoid. Each lacrimal boneis pierced by
an opening ,the LACRIMAL FOSSA, which
serves as a passageway for tears. Lacrimal is
from the word Lacrimae ( means tears) ,
hence it is sometimes called tears bone.

The PALATINE BONE
paired bones posterior to the palatine process;
form posterior hard palate and part of the orbit;
meet medially at the median palatine sutures.

The ZYGOMATIC BONE
Lateral to the maxilla; forms portion of the face
commonly called the cheekbone, and forms part of
the lateral orbit.

The NASAL BONE
small rectangular bones forming the bridge of the
nose
The VOMER
 blade – shaped bone( vomer= plow) in the median
plane of nasal cavity that forms posterior and
inferior nasal septum
The INFERIOR NASAL CONCHAE ( Turbinates)
 thin curved bones protruding medially from the lateral
walls of the nasal cavity; serve the same purpose as the
turbinate portions of the ethmoid bone.
The PARANASAL SINUSES
•Four skull bones- maxillary, sphenoid, ethmoid and frontalcontains sinuses ( mucosa-lined air cavities) that lead to the
nasal passages . These paranasal sinuses lighten the facial
bones and may act as resonance chambers for speech. The
maxillary sinus is the largest of the sinuses found in the
skull.
•Sinusitis or inflammation of the sinuses, occurs
as a result of an allergy or bacterial invasion of the sinus
cavities.
The HYOID BONE
 located in the
throat above the larynx. It serves as a point of
attachment for the many tongue and neck muscles. It does not
articulate with any other bone and is thus unique. It is a horseshoeshaped with a body and two pairs of horns or cornua.
•Extending from the skull to the pelvis , forms the body’s
major axial support.
• surrounds and protects the delicate spinal cord via openings
between adjacent vertebrae
•Consists of 24 single bones called vertebrae and two
composite or fused bones sacrum and the coccyx ,that are
connected in such a way as to provide a flexible curved
structure.
•7 bones of the neck are called cervical vertebrae
•Next 12 bones are called thoracic vertebrae
•5 supporting the lower back are called lumbar vertebrae
•Intervertebral discs , a pads of fibrocartilage that separates
the vertebrae, cushion the vertebrae and absorb shock.
•The CERVICAL VERTEBRAE
•Referred to as C1 through C2, forms the neck portion of the vertebral
column.
• C1 or also known as atlas ,receives the occipital condyles of the skull.
The joint enables you to nod “yes”.
•C2 or also known as axis, acts as pivot point for the rotation of the
atlas (and the skull) above.
•DENS or ODONTOID PROCESS- serves as the pivot point bet. atlas and
the skull
•The articulation between C1 and C2 allows you to rotate your head
from side to side to indicate “ no”.
•Vertebra prominens , spinous process of C7 ,that is visible through
the skin, used as a landmark for counting the vertebrae.
The THORACIC VERTEBRAE
•12 thoracic vertebrae ( referred to as T1 through T12)
•Several characteristics of the thoracic vertebrae:
 larger body than the cervical vertebrae; it is somewhat
heart-shaped, with two small articulating surfaces or costal
facets
 facets articulate with the heads of the corresponding ribs
 oval or round shaped vertebral foramen
 long spinous process , with sharp downward hook
 the closer the thoracic vertebra is to the lumbar region, the
less sharp and shorter the spinous process
 only vertebrae that articulates with the ribs
The Lumbar vertebrae
•Five lumbar vertebrae ( L1 through L5)
•Several characteristics of lumbar vertebrae:
 have massive blocklike bodies and short, thick, hatchetshaped spinous processes extending directly backwards
 the sturdiest of the vertebrae
Spinal cord ends at the superior edge of L2, but the outer
covering of the cord, filled with the cerebrospinal fluid
,extends beyond
Lumbar puncture ( examination of the cerebrospinal fluid)
or the administration of the “saddle block “ anesthesia for
childbirth is normally done bet. L3 or L4 and L5, where ther is
no chanceof injuring the spinal cord.
THE SACRUM
• is a composite bone formed from the fusion of vertebrae
• it articulates with L5 and inferiorly connects with the coccyx
•Median sacral crest, is a remnant of the spinous process of
the fused vertebrae
•Alae or ala, formed by fusion of the transverse processes ,
articulate laterally with the hipbones
•Sacral Foramina, are located at either end of the ridges , it
allows blood vessels and nerves to pass
THE COCCYX
• is formed from the fusion of three to five small
irregularly shaped vertebrae, it is literally the human
tailbone, a vestige of the tail that other vertebrates have
•It is attached to the sacrum by ligaments
The THORACIC CAGE
•Also known as the bony thorax, composed of
the sternum, ribs and thoracic vertebrae.
•Combined with the coastal cartilages it is
called thoracic cage , because of its appearance
and because it forms a protective cone-shaped
enclosure around the organs of the thoracic
cavity.
The STERNUM
•Also known as breastbone ,a typical flat bone, is a result of
the fusion of the three bones , manubrium, body, xiphoid
process
•It is attached to the first seven ribs.
•Supriormost manubrium ,looks like a knot of a tie ; it
articulates with the clavicle ( collar bone) laterally
•Body also known as gladiolus, forms the bulk of the sternum
• Xiphoid Process constructs the inferior end of the sternum
and lies at the level of the fifth intercostal space.
•It is made up of hyaline cartilage for children and ossified in
adults
Bony landmarks of the sternum:
•Jugular notch , concave upper border of the
manubrium, can be palpated easily, it is generally at
the level of the third thoracic vertebra
•Sternal angle ,is the result of the manubrium and
body meeting at a slight angle to each other ,
reference point for counting ribs to locate the second
intercostal space for listening to certain heart valves
and for thoracic surgery
•Xiphisternal Joint , point where the sternal body and
xiphoid process fuse, lies at the level of the ninth
thoracic vertebra
The RIBS
• 12 pairs of ribs forms the walls of the thoracic cage
• all of the ribs articulate posteriorly with the vertebral column via
their heads and tubercles
•First seven pairs are called true ribs or vertebrosternal , attached
directly to the sternum by their own costal cartilages
•Next five pairs are called false ribs ; they are attached indirectly to
the sternum or entirely lack a sterna attachment.
•Rib pair 8 to 10 are also called vertebrochondral , have indirect
cartilage attachments to the sternum via the costal cartilage of the rib
7.
•Floating ribs , last two pairs, have no sterna attachment.