2401 A&P-I
Minimum Departmental Requirements
2401 Anatomy & Physiology I
Exercise 20
The Axial Skeleton
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Structures in red are optional
The axial skeleton is divided into 3 parts:
1. Skull
2. Vertebral column
3. Thoracic cage
The appendicular skeleton is divided into 2 parts:
1. The pectoral and pelvic girdles
2. The upper and lower limbs
The skull
1. Cranial bones enclose and protect fragile bone tissue
 8 large flat bones
2 paired bones: Parietal and temporal
4 single bones: frontal, occipital, sphenoid, ethmoid
2. Facial bones form the base for facial muscles and form an anterior opening for the eyes
 14 bones
12 paired bones: maxillae, palatine, nasal, zygomatic, lacrimal, inferior nasal conchae
2 single bones: mandible, vomer. All skull bones except the mandible are joined by
interlocking joints called sutures.
The Cranium
1. Cranial vault or calvaria
a. Superior, lateral, and posterior walls of the skull
2. Cranial floor or base
a. Anterior fossa
b. Middle fossa
c. Posterior fossa
Sutures of the Skull
 Coronal suture:
 Sagittal suture:
 Lambdoid suture:
 Squamous suture:
between parietal and frontal bones
between parietal bones
between occipital and parietal bones
between parietal and temporal bones
Cranial bones:
1. Frontal bone
 anterior portion of the cranium
 forms forehead, superior part of the orbit, floor of anterior cranial fossa
2. Parietal bone
 Forms sides of the cranium
3. Temporal bone
4. Occipital bone
 Forms floor and back wall of cranium
 Joins sphenoid anteriorly
5. Sphenoid bone
 Bat-shaped bone
 Forms anterior plateau of middle cranial fossa
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The Axial Skeleton
6. Ethmoid bone
 Irregularly shaped bone found anterior to sphenoid
 Forms roof of nasal cavity, upper nasal septum, and medial orbit walls
Activity 1: Identifying the bones of the skull
Cranial Bones:
1. Frontal bone
a. Supraorbital foramen
b. Glabella
2. Parietal bone
a. Sagittal suture
b. Coronal suture
3. Temporal bone
Squamous suture
Zygomatic process
 Zygomatic arch
Mandibular fossa
External auditory meatus
Styloid process
Mastoid process
 Disease: Mastoiditis
 Disease: Meningitis
Stylomastoid foramen
Internal acoustic meatus
4. Occipital bone
a. Foramen magnum
b. Occipital condyle
c. External occipital protuberance
5. Sphenoid bone
a. Greater wings
b. Sella turcica
For the pituitary gland
6. Ethmoid bone
a. Crista galli
b. Cribriform plate
Passageway for olfactory nerves
c. Perpendicular plate
Forms superior part of nasal septum
d. Superior and middle nasal conchae (turbinates)
Facial Bones:
1. Maxillae
a. Alveolar margin
b. Palatine process – anterior hard palate
c. Incisive fossa
2. Mandible
a. Body – horizontal portion
b. Ramus – vertical portion
c. Mandibular condyle – articulates with temporal bone
d. Coronoid process
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2401 A&P-I
e.
f.
g.
h.
Minimum Departmental Requirements
Angle
Alveolar margin – with sockets for teeth
Mental foramen
Mandibular foramen
3. Lacrimal bones
a. pierced by lacrimal fossa (passageway for tears)
4. Palatine bones
5. Zygomatic bones
a. Articulates with zygomatic process of temporal bone forming the zygomatic arch
b. Form the portion of the face called the cheekbone
6. Inferior nasal conchae (turbinates)
Cranial Foramens to Identify
 External view
 Supraorbital foramen
 Infraorbital foramen
 Mental foramen
 Stylomastoid foramen
 Carotid canal
 External auditory meatus-leads to eardrum
 Incisive fossa
 Internal view
 Optic canal
 Superior and inferior orbital fissure
 Foramen rotundum
 Foramen ovale
 Foramen spinosum
 Foramen lacerum
 Jugular foramen
 Internal acoustic meatus
 Hypoglossal canal
 Foramen magnum -for spinal cord
Hyoid Bone
1. Not considered a skull bone
2. Located above the larynx
3. Point of attachment for many tongue and neck muscles
4. Does not articulate with any other bone in the body – unique feature
The Vertebral Column
1. Vertebrae:
 7 cervical
 12 thoracic
 5 Lumbar
 5 sacrum fused
 3 -5 coccyx fused
2. Intervertebral discs: pads if fibrocartilage between vertebrae
 Nucleus pulposus – central soft region
 Annulus fibrosus – outer ring of collagen fibers
o Herniated disc – protrusion of the nucleus pulposus
3. Examining Spinal Curvatures
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2401 Laboratory
4.
5.
6.
7.
8.
9.
The Axial Skeleton
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a. Primary curvatures – present at birth
i. Thoracic – convex
ii. Sacral – convex
b. Secondary curvatures – develops after birth
i. Cervical – concave
ii. Lumbar – concave
c. Abnormal curvatures of spine
i. Kyphosis
ii. Lordosis
iii. Scoliosis
Structure of a Typical Vertebra
a. Body – anterior rounded portion
b. Vertebral foramen – opening for the spinal cord
c. Transverse process – lateral projections
d. Spinous process – single, medial, posterior projection
e. Intervertebral foramina – between 2 adjacent vertebrae, passageway for spinal nerves
Cervical vertebra
a. Transverse foramina
i. Only in cervical vertebra
b. Atlas or C1
i. No body
ii. Joins the head and provides for range of motion (when you nod to say yes)
c. Axis or C2
i. Odontoid process or dens – allows rotation of the head (when you nod to say no)
Thoracic Vertebrae
a. Long spinal process oriented downward
b. No transverse foramen
Lumbar Vertebrae
a. Massive body
b. Short, thick, more horizontal spinous processes
c. No rib facets
d. No transverse foramina
e. Superior and inferior articular processes present
Sacrum
a. Medial sacral crest – remnant of spinous processes
b. Alae – formed by fusion of transverse processes, articulate with hip bones
c. Sacral foramina – passageway for blood vessels and nerves
d. Sacral canal – continuation of the vertebral canal
Sacrum and coccyx
a. Sacral hiatus – inferior opening of sacral canal
b. Sacral promontory – rim on anterior and superior part of sacrum
c. Coccyx – attached to sacrum by ligaments
The Thoracic Cage
1. Sternum
a. Manubrium – articulates with the clavicle
b. Xiphoid process – inferior end made of hyaline cartilage in children but ossified in adults
c. Jugular notch
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d.
e.
2. Ribs
a.
b.
c.
Minimum Departmental Requirements
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Sternal angle – between body and manubrium
Body
Tubercle – inferior
Costal groove – depression along the inferior side
True ribs
i. 1 – 7 are vertebro-sternal ribs
ii. Attached to the sternum through their own “costal” cartilage
d. False ribs
i. 8 – 12
ii. 8 – 10 are vertebro-chondral ribs that attach to the sternum indirectly via the
costal cartilage of rib 7.
iii. 11 – 12 are floating ribs because they are not attached to the sternum
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