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THE AXIAL SKELETON
Chapter 7: pages 211-245
The Axial Skeleton – 80 bones segregated into three major regions (the skull, vertebral column, and bony
thorax)
THE SKULL
Cranium is the portion of the skull that protects the brain.
The skull also includes the facial bones.
All bones of the skull (except for the mandible) are connected by sutures, which are saw-toothed
connections (immovable joints) between the bones of the skull.
CRANIUM
The cranium has 8 bones.
Parietal bones (2) – attachment of temporalis muscle
 sagittal suture – separates parietal bones
 coronal suture – separates parietal bones from frontal bone
Frontal Bone – attachment of frontalis muscle
 supraorbital margin – thickening over the eye
 supraorbital foramen – nerves/vessels passageway for eyelid, eyebrow, and forehead
 supraorbital notch – where vessels to forehead cross orbital rim
 frontal sinus: one of the paranasal sinuses
 frontal squama – anterior superior forehead; attachment of facial muscles
 lacrimal fossa – superior lateral surface of orbit; location of tear gland
Occipital Bone – attachment of occipitalis muscle
 lambdoidal suture - separates parietal bones from occipital bone
 foramen magnum – “big hole” – allows spinal cord to pass into skull
 occipital condyles – articulate with first vertebrae (atlas) of spine
 external occipital protuberance – attachment for trapezius and other muscles
 external occipital crest – ligament attachment that stabilizes cervical vertebrae
 hypoglossal canals – passage of cranial nerves that control tongue muscles
Temporal bones (2) – attachment of temporalis muscle
 squamous sutures - separates parietal bones from temporal bones
 external acoustic (auditory) meatus – ear canal
 zygomatic process (arch)– joins zygomatic bone
 styloid process – attachment of neck muscles
 mastoid process – attachment of neck muscles and contains mastoid sinus
 stylomastoid foramen – posterior to base of mastoid process; facial nerve passage
 jugular foramen – passageway of jugular vein (between occipital and temporal)
 carotid canal (foramen lacerum) - anterior to jugular foramen; passageway of carotid artery
 condylar (mandibular) fossa - articulation point for condylar process of mandible
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Sphenoid Bone – floor of cranium, unites facial & cranial bones
 sella turcica “Turk’s saddle”
 hypophyseal fossa – depression of sella turcica; holds pituitary in place
 sphenoid sinuses: one of the paranasal sinuses
 foramen ovale – passageway of nerves and vessels
 optic foramen – passageway of optic nerve and vessels
 greater wings – extend laterally from the body of sphenoid
 lesser wings – extends horizontally anterior to sella turcica
Ethmoid Bone
 crista galli “cock’s comb” – covering of brain attaches
 cribiform plates – contains olfactory foramina
 olfactory faromina – passageways for olfactory nerves within cribiform plates
 superior and middle nasal concha – increase surface area of the nasal cavity
 perpendicular plate - makes up the nasal septum along with the vomer
 ethmoidal sinuses: one of the paranasal sinuses
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Paranasal sinuses – sinuses that are positioned around the nasal cavity
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frontal sinus
sphenoid sinuses
ethmoidal sinuses
maxillary sinus
Function – the sinuses lighten the skull, act as resonating chambers
for speech, and produce mucus to moisten and clean inhaled air
Infection – since the paranasal sinuses are so closely related to the
nasal cavity they are commonly infected. A sinus infection can
create discomfort in any of the paranasal sinuses. A build up of
mucus changes the resonating ability of the sinuses and therefore
changes our speech
FACIAL BONES
There are 14 facial bones.
Mandible
 body – chin (horizontal)
 rami (ramus)– upright bars (vertical)
 alveoli (alveolar process) - teeth sockets
 condylar process - articulates with temporal bone
 coronoid process – attachment of temporalis and masseter muslces
 mandibular foramen – interior entry of nerves and vessels of mandible
 mental foramen – exterior exit of mental nerves and vessels (lips and teeth)
 mandibular angle – most posterior inferior aspect between body and ramus
 mandibular notch – notch between the coronoid and condylar processes
 mental protuberance – attachment for several facial muscles
Maxillae (2) – supports teeth of upper jaw as well as forms inferior orbital rim, hard palate, and lateral
margins of nasal cavity
 palatine processes – form anterior hard palate (failure of the palatine processes to fuse medially
results in a cleft palate)
 infraorbital foramen – passageway of infraorbital nerve and vessels; lower eyelid, upper lips,
nostrils
 maxillary sinus: one of the paranasal sinuses
 alveoli (alveolar process) - teeth sockets
 inferior orbital fissure – passage of cranial nerves to eyelids
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Palatine Bones (2) – forms posterior hard palate
Lacrimal Bones (2) – forms medial optic orbit
Nasal bones (2) – forms bridge of nose
Zygomatic bones (2) – forms orbit rim and lateral wall; zygomatic arch
 Zygomaticofacial foramen- passageway of zygomaticalfacial nerve & vessels; cheek
 Temoral process – portion of arch closest to temporal bone
Vomer Bone (Vomer = plow) – forms midline of nasal cavity with perpendicular plate of ethmoid bone
Inferior Conchae (kong’ke) (2) – increase surface area of the nasal cavity
OTHER BONES ASSOCIATED WITH THE SKULL
Hyoid Bone – not really part of the skull, but very closely
associated; serves as a movable base for the tongue and an
attachment point for neck muscles that raise and lower the
larynx as we swallow
 Body – main portion
 greater cornua - larger horns
 lesser cornua – smaller horns
Both cornua are sites of muscle attachment
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Auditory ossicles – bones in inner ear; Malleus, Incus, and Stapes
Malleus – hammer
Incus – anvil
Stapes - stirrup
Additional Individualized Bones - Sometimes tiny fragments of bone are separated from the major bones
of the skull by sutures. These tiny bones are called Sutural Bones or Wormian Bones. Not all skulls
have these bones, and for those that do, the number may vary between individuals.
THE FETAL SKULL
Difference in proportions:
 The skull of an adult is 1/8 the length of
the body.
 The skull of a fetus or newborn is ¼ the
length of the body.
 In addition, an infant’s face is very small
compared to the size of its cranium.
When a baby is born, the skull is not completely
formed. Fibrous membranes called fontanels
connect the infant’s cranial bones creating “soft
spots”. The fontanels allow the skull to be
compressed slightly during childbirth and allow
the brain to grow. The fontanels are replaced by
bone within 22 to 24 months after birth.
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THE VERTEBRAL COLUMN (SPINE)
Consists of 26 irregular bones
Before birth the spine consists of 33 separate
vertebrae, but 9 of these fuse forming two
composite bones called the sacrum and coccyx.
The central cavity of the vertebral column
contains the spinal cord which it surrounds and
protects. The spinal cord continues into the
sacrum as the sacral canal.
The vertebrae are separated by intervertebral
discs composed of fibrocartilage.
Herniated or slipped discs can cause pressure to
the spinal cord creating pain or numbness.
SPINAL CURVATURES
The vertebrae are connected and reinforced by ligaments in such a way that a flexible curved structure
results. The spinal curvatures in the thoracic and sacral regions are referred to as primary curvatures
because they are present when we are born. They can also be called accommodation curves, as they
accommodate the abdominopelvic and thoracic viscera. The secondary curvatures include the cervical
curvature and the lumbar curvature. These curvatures appear as a baby begins to raise its head and walk
respectively. The secondary curves can also be called the compensation curves as they help shift the
weight to allow for upright posture. All four curves are fully developed by age 10.
Abnormal curvatures include: Kyphosis, Lordosis, and Scoliosis (page 232)
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ANATOMY OF A VERTEBRA
 Vertebral Body or Centrum: disc-like weight bearing portion facing anteriorly in the vertebral
column; connected together by ligaments, separated by fibrocartilaginous discs
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Vertebral Arch: arch formed from the joining of all posterior extensions, the laminae and pedicles,
from the ventral body
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Vertebral Foramen: canal through which the spinal cord passes
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Transverse Processes: two lateral projections from the body; articulates with tubercles of ribs;
points of muscle attachment
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Spinous Process: single projection arising from the posterior aspect of the vertebral arch (actually
the fused laminae)
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Superior and Inferior Articular processes: paired projections lateral to the vertebral foramen,
allowing the vertebra to form joints with adjacent vertebra
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Articular facet – smooth concave surface on each superior and inferior articular process where two
vertebrae articulate with one another (the articular facets are located on the dorsal side of the
superior articular process and on the ventral side of the inferior articular process).
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Lamina – form roof of vertebral arch; located between transverse processes and spinous process
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Pedicle – segment between transverse process and vertebral body; walls of the vertebral arch
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Intervertebral foramina – gaps in between the pedicles of successive vertebrae which allow nerves
to pass to and from the spinal cord
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3 DIVISIONS OF VERTEBRAE
Cervical vertebrae – (C1-C7) Neck region.
C1 is called the atlas and has no body. Articulates with the occipital condyles of the head.
Allows the head to nod “YES”. (Greek mythology – Atlas holds the world on his shoulders).
C2 is called the axis acts as a pivot for the rotation of the atlas. Allows your head to twist from
side to side to indicate “NO”.
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Dens or Odontoid process – “tooth” – pivot point on which atlas and skull can rotate
around
Transverse foramina – the cervical vertebrae contain small openings that allow vertebral
arteries and veins to pass and serve the brain
Thoracic vertebrae – (T1 – T12) Upper and
middle back regions. Each articulates with one
or more pairs of ribs
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Costal Facets – located on the
dorsolateral surfaces of the thoracic
vertebral bodies; articulate with the
heads of the ribs. T1 – T8 each articulate
with two ribs and have two facets on
each side of the vertebral body. T9 –
T11 each articulate with one pair of ribs
and therefore only have one facet on
each side of the body.
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Transverse costal facets – located on
vertebrae T1 – T10. Rib pairs 1-10
contact their vertebrae at two points; a
costal facet and a transverse facet
Lumbar vertebrae – (L1 – L5) Lower back
region. Bear the most weight. Larger body and
smaller vertebral foramen.
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SACRUM (sacral) AND COCCYX (coccygeal)
Sacrum (5 fused bones, begin fusing after puberty and completely fused by age 25-30).
Provides and extensive area for muscle attachment (thigh).
 sacral canal – houses sacral nerves (end of the spinal cord)
 sacral cornua – laminae of the 5th sacral vertebrae fail to meet each other at the midline,
forming these two ridges on the lateral sides of the sacral hiatus
 sacral hiatus – opening at the inferior end of the sacral canal; covered by connective
tissue
 sacral foramina – allows exit of sacral nerves
 median sacral crest – posterior ridge along the center of the sacrum, formed by fused
spinous processes
 lateral sacral crests - posterior ridges along the sides of the sacrum, formed by fused
transverse processes
 auricular surface (sacroiliac joint) – point of articulation between sacrum and ileum
 sacral tuberosity – roughened area between the lateral sacral crest and the auricular
surface; attachment sites of ligaments that stabilize the sacroiliac joint
 articular process – joint with 5th lumbar vertebra
 sacral promontory – bulge at the anterior superior sacrum; important landmark for female
pelvic exams and in labor and delivery
Coccyx (tailbone; 3-5 but typically 4 fused bones, fusing begins by age 26). Attachment site for
number of ligaments and for a muscle that constricts the anal canal
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Coccygeal cornua – prominent laminae of the of the first coccygeal vertebrae
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THE BONY THORAX
Composed of the Ribs, Sternum, and Thoracic Vertebrae
Characteristics:
 Provides a protective cage for the vital organs of the thoracic cavity (heart, lungs, thymus, and
great blood vessels)
 Supports the shoulders and upper limbs
 Provides attachment points for major muscles of the neck, back, chest, and shoulders
In addition, the spaces between the ribs are occupied by intercostal muscles, which lift and contract the
thorax during breathing.
STERNUM (breastbone)
Is a typical flat bone and is divided into three parts (based on the fusion of three bones). :
 Manubrium – articulates with clavicles and 1st rib cartilages
i. Jugular notch – shallow indentation on superior surface
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Body of the sternum – costal cartilages of ribs 2-7 attach
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Xiphoid Process- diaphragm and rectus abdominus muscles attach
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RIBS
There are 12 pairs of ribs
True ribs: 7 pairs that are directly attached to the sternum by costal cartilages
 Costal Cartilages – connect ribs to sternum
False ribs The remaining 5 pairs of ribs that either do not attach directly to the sternum or do not
attach at all (includes the floating ribs)
Ribs pairs 11 and 12 are called Floating Ribs because they lack sternal attachment
Ribs increase in length from 1-7, then decrease in length from pair 8-12
The intercostal spaces (between ribs) are filled with intercostal muscles that aid in breathing.
Rib Features:
 Vertebral end – the portion that contacts the vertebrae
o Head (capitulum) – articulates with vertebral body
 Inferior and superior articular facets – found on head; separated
by a ridge
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o Neck – narrow section between the head and tubercle
o Tubercle – contains a facet that articulates with vertebral transverse
process
o Angle – bend between the body and tubercle
Body – long portion of rib (shaft)
o Costal groove – located on inferior border of body; passing of nerves and
vessels
Sternal Extremity (end) - articulates with sternum
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angle
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