summary of anatomy 2

8/8/2019 Summary of Anatomy 2

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مبسم هللا المحرن الرحي

The Axial Skeleton

Divisions of the Skeletal System:

- The adult skeleton consists of 206 named bones.

- The skeleton of infants and children has more than 206 bones because some of their bones (hipand backbone) fuse later in life.

- There are two principal divisions in the adult skeleton:

1. The Axial Skeleton No. 2. The Appendicular Skeleton No.

Cranium 8 Clavicle 2Skull

Face 14

Pectoral (shoulder)

girdles

Scapula 2Hyoid bone 1

Auditory Ossicles 6 Humerus 2

Vertebral Column 26 Ulna 2

Radius 2

Sternum 1 Carpals 16Thorax

Ribs 24 Metacarpals 10

Upper limbs

Phalanges 28

Pelvic (hip) girdle Hip, pelvic, or

coxal bone 2

Femur 2

Fibula 2

Tibia 2

Patella 2

Tarsal 14

Metatarsal 10

Lower limbs

Phalanges 28

*Girdles: are bones connecting the limbs to the axial skeleton.

Types of bones:- Almost all the bones of the body can be classified into 5 principal types on

basis of shape into:

1. Long bones:- They have greater length than width.

- They are slightly curved for strength (absorb the stress of

body weight, if not curved they will fracture)



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- Consist mostly of compact bone tissue, but

they also contain considerable amounts of spongy bone tissue.

- Include: Thigh ( femur), leg ( tibia and fibula),

toes ( phalanges), arm ( humerus), forearm

(ulna and radius) and fingers ( phalanges).

2. Short bones:- They are somewhat cube-shaped and nearly

equal in length and width.

- Consist of spongy bone except at the surface,

where there is a thin layer of compact bone.- Include: wrist or carpal bones (except for the

pisiform which is a sesamoid bone), and ankle

or tarsal bones (except for the calcaneus

which is an irregular bone)

3. Flat bones:

- They are thin and composed of two parallel plates of compact bone (external and

internal tables), enclosing a layer of spongy bone (diploe).- Their functions: protection and provide extensive areas for muscle attachment.

- Include: the cranial bones, the breastbone ( sternum), ribs and the shoulder blades

( scapulae).

4. Irregular bones:

- They have complex shapes.

- They also vary in the amount of spongy and compact bone present.

- Include: the backbones (vertebrae) and certain facial

bones.

5. Sesamoid bones:

- Meaning shaped like a sesame seed.

- Found in certain tendons where there is considerable

friction, tension and physical stress.- They are not always completely ossified and measure

only few millimeters in diameter except for the two

patellae (kneecaps).

- Function: protect tendons from excessive wear and

tear.

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Include: two sesamoid bones in metacarpophalangeal joint of the thumb in hand, side from the patellae, andtwo sesamoid bones in the plantar surface of the foot at the metatarsophalangeal joint

of great toe.

* An additional type not included in this classification by shape, but by location:

- Sutural or Wormian bones: are small bones located in the sutures of certain cranial bones

and varies in number from person to person.

• During the active growth of skeleton, the red bone marrow is replaced by yellow bone

marrow in most of long bones.

• In adults the red bone marrow is restricted to (ribs, sternum, skull, vertebrae, hip bones,

proximal epiphyses of femur and humerus).



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The Bone Surface markings:

Depressions and OpeningsSites allowing the passage of soft tissues (nerves, blood vessels, ligaments,

tendons)

Fissure Narrow slit between adjacent parts of bones

Foramen Opening through which blood vessels, nerves or ligaments pass.Fossa Shallow depression

SulcusFurrow (groove) along bone surface that accommodates a blood vessel,

nerve, or tendon.

Meatus Tubelike opening (passageway)

ProcessesProjections or outgrowths on bone that form joints or attachment points for

connective tissue.

Condyle Large, round protuberance at the end of a bone

Facet Smooth flat surface

Head Rounded articular projection support the neck of a bone

Crest Prominent ridge or elongated projection

Epicondyle Projection above a condyle

Line Long, narrow ridge or border (less prominent than crest)

Spinous process Sharp, slender projection

Trochanter Very large projection on the femur

Tubercle Small, rounded projection

Tuberosity Large, rounded roughened projection

The Skull:

- Consists of 22 bones, rests on the superior end of vertebral column.- It includes 2 sets of bones:

Cranial bones Facial bones

Frontal (1)

Parietal (2)

Temporal (2)

Occipital (1)

Sphenoid (1)

Ethmoid (1)

Nasal (2)

Maxilla (2)Zygomatic (2)

Mandible (1)

Lacrimal (2)

Palatine (2)Inferior nasal Conchae (2)

Vomer (1)

- The cranial cavity forms smaller cavities including the nasal cavity and orbit and paranasal

sinuses, also hearing and equilibrium cavities.

- The mandible is the only movable bone of the skull.- The bones of the skull are held together by immovable joints called sutures.

Frontal Bone:

- Forms the fore head, the roof of the orbit s and most of the anterior part of the cranial floor.



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- Soon after birth the left and right sides of the frontal

bone are united by the metopic suture, which usually

disappears by age 6~8.

- The frontal squama, a scalelike plate of bone that

forms the forehead.

- Superior to the orbits the frontal bone thickens,

forming the supraorbital margin.- From this margin the frontal bone extends posteriorly

to form the roof of the orbit and part of the floor of

cranial cavity.

- Supraorbital foramen is a hole within the supraorbitalmargin and slightly medial to its midpoint.

- The frontal sinuses lie deep to the frontal squama (mucous membrane lined cavities act as sound

champers that give the voice its resonance).

Parietal Bone:

- The two parietal bones form the greater portion of the sides and roof of the cranial cavity.

- The internal surface of them contains many protrusions and depressions that accommodate the

blood vessels and supplying the dura mater (superficial membrane covering the brain).

- There are no foramina in the parietal bones.

Temporal Bones:

- The two temporal bones form the inferior lateral aspect of the cranium and part of the cranial floor.

- Temporal Squama: is the thin, flat portion of the temporal bone that forms the anterior and superior part of the

Temple.

- Zygomatic process is a projection from the inferior portion of the temporal squama which forms a joint with

temporal process of the zygomatic bone.

- The Zygomatic arch: is formed from the zygomatic process of the temporal bone and the temporal process of

the zygomatic bone. - Mandibular fossa: is a socket on the inferior posterior surface of the zygomatic process of

temporal bone.

- Articular Tubercle: is a rounded elevation anterior to the mandibular fossa.

- The mandibular fossa and the articular tubercle articulate (form a joint) with the mandible to formthe temporomandibular joint (TMJ).

- The Mastoid portion is located posteriorly on the temporal bone and inferior, posterior to external

auditory meatus (ear canal).

- This portion contains several mastoid air cells these tiny air-filled compartments are separated

from the brain by thin bony portion.

- The mastoid process is a rounded projection of the mastoid portion posterior to the external

auditory meatus and serves as point of attachment for several neck muscles.- Internal auditory meatus: is the opening through which the facial and vestibulocochlear cranial

nerves pass.



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The styloid process projects inferiorly from the inferior surface of the temporal bone and serves as a

point of attachment for muscles and ligaments of the tongue and neck.

- Petrous portion of temporal bone is located at the floor of the cranial cavity, triangular and located

at the base of the skull between the sphenoid and occipital bones, houses the (internal and middle)

ear.

- Foramens: carotid foramen, jugular foramen and stylomastoid foramen.

Occipital Bone:

- forms the posterior part and the most of the cranium.

- Foramens: magnum foramen, hypoglossal foramen.

- The occipital condyles are oval processes with convex surfaces, one on either side of the foramen

magnum.

- They articulate with depressions on the first cervical vertebra (Atlas) to form the atlanto-occipital

joints.

- The external occipital protuberance is a prominent midline projection on the posterior surface of the bone just superior to the foramen magnum.

- The ligamentum nuchae is a large fibrous elastic ligament extends from the external occipital

protuberance to the 7th

cervical vertebra.

- The superior and inferior nuchal lines are areas of muscle attachment extend laterally from the

protuberance.

Sphenoid bone:

- It lies at the middle part of base of the skull.

- It is called the keystone of the cranial bones because it articulate with all the other of cranial bones.- Sphenoid bone articulations:Anteriorly with frontal bone,

• Laterally with temporal bone,

• Posteriorly with the occipital bone.

- Its shape is like a bat.

- The body of sphenoid is the cubelike medial portion between

the ethmoid and occipital bone.

- It contains sphenoid sinuses, which drain into nasal cavity.

- Sella turcica: is a depression on the superior surface of body of

sphenoid, which cradles the pituitary gland.

- The greater wings of the sphenoid project laterally, forming the anteriolateral floor of cranium.- The lesser wings of sphenoid are smaller from greater wings, forming a ridge of bone anterior and

superior to the greater wings.

- They form part of floor of cranium and posterior part of the orbit .

- The optic foramen is located between the body and lesser wings just anterior to sella turcica.- The superior orbital fissure is triangular slit lateral to the body and between the greater and lesser

wings.

- The pterygoid processes extending from the inferior part of sphenoid bone and form the lateral

posterior region of the nasal cavity.

- Foramens: foramen ovale, foramen spinosum, foramen lacerum and foramen rotundum.



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Ethmoid Bone:

- The ethmoid bone is a light, spongelike bone located on the midline in the anterior part pf the

cranial floor medial to the orbits.

- It is anterior to sphenoid bone and posterior to the nasal

bones.- The ethmoid forms:

• Part of the anterior potion of cranial floor.

• The medial wall of the orbits

• The superior portions of the nasal septum

• And most of the superior sidewalls of the nasal cavity.

- The lateral masses of ethmoid bone contain 3~18 air spaces

or cells (together form the ethmoidal sinuses)

- Its parts are:

• The perpendicular plate forms the superior portion of

the nasal septum.

• The cribriform plate lies in the anterior floor of cranium and forms the roof of nasal cavity,

contains the olfactory foramina.

• The crista galli is a sharp triangular process projecting superiorly from the cribriform plate.

• The superior nasal concha and the middle nasal concha are lateral masses of the ethmoidand project lateral to the nasal cavity, they increase the vascular and mucous membrane

surface area in the nasal cavities (warm and moisten the inhaled air).

• The inferior nasal conchae are separate bones and not part of ethmoid.

Nasal Bones:

- The paired nasal bones meet at the midline and form part of the bridge of the nose.

- The major structural portion of the nose consists of cartilage.

Maxillae:

- The paired maxilla unite to form the upper jaw bone and articulate directly with every bone of the

face except the mandible.- They form part of the floor of the orbits, part of the lateral walls and floor of the nasal cavity, and

the most of the hard palate.

- The hard palate: is a bony partition formed by the palatine processes of the maxilla and the

horizontal plates of the palatine bones that form the roof of the mouth.

- Each maxilla contains a large maxillary sinus that empties in the nasal cavity.

- The alveolar process: is an arch contains the alveoli "sockets" for the maxillary teeth.

- The palatine process is a horizontal projection of the maxilla that forms the anterior 3/4 of the hardpalate.

- The union and fusion of maxillae is normally completed before birth.

- Foramens: incisive foramen and infraorbital foramen.

Zygomatic Bones:

- The two zygomatic bones called cheek bones.



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- They articulate with the frontal, maxilla, sphenoid, and temporal bones.

- Its parts:

• The temporal process of zygomatic bone projects posteriorly and articulates with the

zygomatic process of temporal bone to from the zygomatic arch.

• Foramen: the zygomaticofacial foramen near the center of it.

Lacrimal Bones:

- They are paired and resemble a fingernail in size and shape.

- These bones (the smallest bones of the face) are posterior and lateral to the nasal bones and form

apart of the medial wall of each orbit.

- Each lacrimal bone contains a lacrimal fossa, a vertical tunnel formed with the maxilla, which

houses the lacrimal sac (a structure that gathers tears and passes them into nasal cavity).

Palatine Bones:

- The two L-shaped palatine bones form the posterior portion of the hard palate, part of the floor,

and the lateral wall of the nasal cavity, and a small portion of the floors of the orbits.

- The posterior portion of the hard palate, which separates the nasal cavity from the oral cavity, is

formed by the horizontal plates of the palatine bones.

Inferior Nasal Conchae:

- They are separated bone and nit part of ethmoid bone.

- Their function resembles the function of superior and middle conchae but not involved in the

sense of smell.

- They form part of the inferior lateral wall of nasal cavity.

Vomer:

- It is a roughly triangular bone on the floor of the nasal cavity.

- Articulates superiorly with the perpendicular plate of the ethmoid bone and inferiorly with both

the maxilla and the palatine bones along the midline.

- It is one of the components of the nasal septum.

Mandible:

- The mandible is the largest and strongest facial bone.

- It is the only movable skull bone.

- It consists a curved horizontal portion called body, and two perpendicular portions the rami (2

ramus)

- The angle of mandible is the area where each ramus meets the body.

- Each ramus has a posterior codylar process that articulates with the mandibular fossa and

articular tubercle of the temporal bone to form the TMJ.

- It has also an anterior coronoid process to which the temporalis muscle attaches.- The mandibular notch: is the depression between the coronoid process and the condylar process.

- The alveolar process is an arch containing the alveoli of the mandibular teeth.



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- Foramens: mental foramen and mandibular foramen.

- The mandibular canal runs obliquely in the ramus and anteriorly to the body, through which

inferior alveolar nerves and blood vessels pass.

Sutures of the Skull:

- The suture is an immovable joint that is found only between skull bones and that holds most skull

bones together.- How the margins of the bones unite:

1. Smooth margins.

2. overlap margins

3. Interlock in jigsaw fashion (provides strength and decrease the chance of fracture).

- The prominent sutures:

1. Coronal suture:- unites frontal bone and both parietal bones.

2. Sagittal suture: unites the two parietal bones on the superior midline of the skull.

3. Lambdoid suture: unites both parietal bones and occipital bone.

4. Squamous suture: unites the parietal and temporal bones on the lateral aspect of the skull.

Fontanels:

- They are called commonly soft spots, areas of fibrous connective tissue membranes that will

eventually be replaced with bone and intramembranous ossification and become sutures.

- The importance of them:

• Modify fetal skull size and shape as it passes through the birth canal.

• Permit rapid growth o the brain during infancy.

• The amount of its closure determines the degree of development.

- Table 6.4 p 151.

Foramina of the Skull:



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Nasal Septum:- It is vertical partition that divides the nasal cavity into right and left sides.

- It is formed by the vomer , septal cartilage (hyaline cartilage) and the perpendicular plate of

thmoid bone.

- The vomer articulates:

Anteriorly with the septal cartilage forming the anterior

portion of the septum. Superiorly perpendicular plate of ethmoid bone forming

the remainder of the nasal septum.

Orbits:

-Each orbit (eye socket) is a pyramid shape structure that

contains the eyeball and associated structures.

-it is formed by seven bones of the skull and has 4 regions that converge posteriorly to form an

apex:

• The roof : frontal and sphenoid bones.

• The lateral walls: zygomatic and sphenoid bones.

• The floor : maxilla, zygomatic and palatine bones.

• The medial wall: maxilla, lacrimal, ethmoid and

sphenoid.

-Associated opening with the orbit:

1. Obtic foramen: at the junction of the roof andmedial wall.

2. Superior orbital fissure: at the superior lateral angle

of the apex.

3. Inferior orbital fissure: at the junction of the lateralwall and floor.

4. Supraorbital foramen: on the medial side of the supra orbital margin of the frontal bone.

5. Lacrimal fossa: in the lacrimal bone.

Cranial Fossae:-The floor of cranium contains 3 distinct levels from anterior to posterior.-The fossae contains depressions for the various brain convolutions, grooves for cranial blood

vessels and numerous foramena.

1.

Anterior cranial fossa:- It is the highest level.

- Formed from the portion of frontal bone that

constitutes the roof of the orbits and nasal

cavity, the crista galli and creibriform plate of

the ethmoid bone, the lesser wings and part of

the body of sphenoid bone.

- It houses the frontal lobes of the cerebral

hemispheres of the brain.



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2. The middle cranial fossa:

- Is inferior and posterior to the anterior cranial fossa.

- It's shaped like a butterfly with a small median portion and two expanded lateral

portions.

- The median portion is formed by part of the body of the sphenoid bone.

- The lateral portion is formed by the greater wings of the sphenoid bone, temporal

squama and parietal bone.

- It houses the temporal lobes of the cerebral hemispheres.3. The posterior cranial fossa:

- At the most inferior level.

- The largest of the fossae.

- It is formed by occipital bone and the petrous, and mastoid portion of the temporalbone.

- It houses cerebellum, pons and medulla oblongata.

Hyoid Bone:

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The single hyoid bone is a unique component of the axial skeleton because it does not articulate

with any other bone and suspended from thestyloid processes of the temporal bones by

ligaments and muscles. - It is located in the anterior neck between the

mandible and larynx. - It supports the tongue providing attachment site

for some tongue muscles and four muscles of

the neck and the pharynx.

- It consists of a horizontal body and pairedprojections called greater and lesser horns

(muscle attachment).

Vertebral Column:

- It is also called Spine or Backbone.- The bone and connective tissue of vertebral column form a

strong, flexible rod that bends anteriorly, poteriorly,

laterally and rotates.- It encloses and protects the spinal cord , supports the head,

and serves as a point of attachment for the ribs, pelvic

girdle, and muscles of the back.

- It makes up about 2/5 of the total height of the body and is

composed of a series of bones called vertebrae.

- Between the vertebrae are openings called intervertebral

foramina through which the thoracic and lumbar spinal



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nerves connect the spinal cord to the various parts of the body.

- The adult vertebral column is divided into 5 regions that contain 26 vertebrae:

1. The cervical region contains 7 cervical vertebrae.

2. The thoracic region contains 12 thoracic vertebrae.

3. The lumbar region contains 5 lumbar vertebrae.

4. The sacral region contains sacrum (one bone consisting of 5 fused sacral vertebrae.

5. The coccygeal region contains one bone called the coccyx, which consists of usually 4 fused

coccygeal vertebrae.

- Before the sacral and coccygeal vertebrae fuse, the total number of vertebrae is 33.- All of above bones are movable except the sacrum and coccyx bones.

Intervertebral Discs:- They are between the bodies of adjacent vertebrae from the 2

ndcervical vertebra to the sacrum.

- Each disc has:

• An outer fibrous ring consisting of fibrocartilage called annulus fibrosus.

• An inner soft, pulpy, highly elastic substance called nucleus pulposus.

- The discs form strong joints, permit various movements of vertebral column, and absorb vertical

shock (flatten, broaden, and bulge under compression).

Normal curves:When viewed from side, the vertebral column shows 4 normal curves:

• The cervical and lumbar curves are anteriorly convex.

• The thoracic and sacral curves are anteriorly concave.

- The importance of these curves:

• They increase its strength; help maintain balance in the upright position.

• Absorb shocks during walking and running.

• Protect the column from fracture.- In the fetus there is only a single anteriorly concave curve.

- In the infant (at 3rd

month after birth) the cervical and lumbar curves develop and are called

secondary curves because they form later.

- But the thoracic and sacral curves are called primary curves because they form first during fetal

development.

- All curves are fully developed by age 10.

Parts of a typical vertebra:- The vertebrae along the vertebral column vary in size, shape and details but have the same

structures:Body:

- It is the thick, disc-shaped anterior portion that is the weight-bearing part of a vertebra.

- Its superior and inferior faces are roughened for attachment of cartilaginous intervertebral

discs.

- The anterior and lateral surfaces contain nutrient foramina for blood vessels.

Vertebral Arch:- It extends posteriorly from the body of vertebra.

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- It is formed by two short thick processes called pedicles, which project posteriorly from the

body to unite with the laminae.

- The laminae are flat parts that join to form the posterior potion of the vertebral arch.

- The vertebral foramen lies between the vertebral

arch and the body and contains spinal cord, fat,

areolar connective tissue, and blood vessels.

- The vertebral foramina of all vertebrae form the

vertebral (spinal) canal .

- The pedicles exhibit superior and inferiornotches called vertebral notches (one from

above vertebra and one from lower vertebra form

the intervertebral foramina on each side of

vertebral column) through which a single spinalnerve pass.

Processes:- Seven processes arise from the vertebral arch:

o Two Transverse process: extends laterally at the point where a lamina and pedicle join on

each side.

o A single spinous process: projects posteriorly from the junction of the laminae.o Two superior articular processes: form a joint with the above vertebra.

o Two inferior articular processes: form a joint with the below vertebra.

- The articulating surfaces of the articular processes are called facets.

- The articulation formed between the bodies and articular facets of successive vertebrae are called

intervertebral joints.

Regions of vertebral columns in details:

Cervical region:- The bodies of cervical vertebrae are smaller than the thoracic vertebrae.

- The vertebral arches are larger.

- All cervical vertebrae have 3 foramina: 1 vertebral foramen and 2 transverse foramina.

- The vertebral foramina are the largest in spinal column because they house the cervical

enlargement of spinal cord.

- Each cervical transverse process contains a

transverse foramen through which the

vertebral artery and vein and nerve fibers

pass.

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The spinous processes of C2 through C6 areoften bifid (split into two parts).

- The first two cervical vertebrae differ fromthe others.

- The Atlas (C1) is a ring of bone withanterior and posterior arches and large

lateral masses. It has not a body and spinous process.- The superior articular facets of lateral masses of atlas are concave and articulate with the

occipital condyles of the occipital bone to form the atlanto-occipital joints.

- This articulation seen when moving the head to say "yes".

- The inferior articular facets articulate with the second cervical vertebra.- The transverse processes and transverse foramina of atlas are quite large.



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- The second cervical vertebra (C2), called axis has a body.

- It has a process called dens or odontoid process projects superiorly through the anterior

portion of vertebral foramen of atlas.

- The dens makes a pivot in which the atlas and head rotate when

saying "no".

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The atlanto-axial joint formed between the anterior arch of atlasand dens of axis.

- From C3 to C6 vertebrae resemble the typical cervical vertebra.

- The C7 called cervical prominens, has a single large spinous

process that felt at the base of the neck.

Thoracic region:- The thoracic vertebrae are larger and stronger than cervical ones.

- The spinous processes of T1 and T2 are long, laterally flattened, and directed inferiorly but

the spinous processes of T11 and t12 are shorter, broader,

and directed more posteriorly.- The distinguished feature of

thoracic vertebrae is that they

articulate with the ribs in

articular surfaces called facets

and demifacets (half-facets).

- Except for T11 and T12, thetransverse processes have

facets for articulating with the tubercles of the ribs.

- The bodies of thoracic vertebrae have also facets ordemifacets for articulation with the heads of the ribs.

- The articulation between the t T vertebrae and ribs called vertebrocostal joint.

• T1 has a superior facet and inferior demifacet on each side.

• T2-T8 have a superior and inferior demifacets.

• T9 has a superior demifacet on each side.

• T10-T12 have superior facets on each side.

- The movement of thoracic region is limited by thin intervertebral discs and by attachment of

the ribs to sternum.

Lumbar region: - The lumbar vertebrae are the largest and strongest

because the amount of body weight supported by

vertebrae increases toward the inferior end of the

backbone.

- Their projections are short and thick.

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- The superior articular processes are directed medially instead of superiorly, and the inferior

articular processes are directed laterally instead of inferiorly.

- The spinous processes are quadrilateral in shape, thick and broad, and project nearly straight

posteriorly.

Sacrum: - It is a triangular bone formed by union of 5 sacral vertebrae (S1~S5).

- They started to fuse between 16 and 18 years of age, and completed by age 30.- It is positioned at the posterior portion of the

pelvic cavity medial to the two hip bones.

- The female sacrum is shorter, wider, and

more curved between S2 and S3 than themale sacrum.

- They are concave anteriorly (face the pelvic

cavity).

- It is smooth and contains 4 transverse lines

(ridges) (the joining lines between the

bodies).

- At the ends of these lines are 4 pairs of anterior sacral foramina.

- The lateral portion of superior surface contains a smooth surface called sacra ala (= wing),

formed by the fused transverse processes of 1st

sacral vertebrae S1.

- The posterior surface of sacrum is convex and contains the median sacral crest which is the

fused spinous processes of the upper sacral vertebrae.

- The lateral sacral crest is the fused transverse processes of the sacral vertebrae and the 4

pairs of posterior sacral foramina.

- The sacral canal is a continuation of vertebral canal.

- The laminae of the S5 and sometimes S4, fail to meet and this leaves an inferior entrance to

the vertebral canal called the sacral hiatus.

- On both sides of sacral hiatus are the sacral cornua (cornu), which is the inferior articular

processes of S5, and they are connected by ligaments to the coccyx.- The narrow inferior portion of sacrum is called apex, and the broad superior portion is

called the base.

- The anteriorly projecting border of the base is called sacral promontory (used for

measurement of pelvis).

- Both lateral surfaces of sacrum is called auricular surface (=ear), that articulate with the

ilium of each hip bone to form sacroiliac joint.- Posterior to the auricular surface is the sacral tuberosity, which contains depressions forattachment of ligaments.

- The superior articular processes of the sacrum articulate with the 5th

lumbar vertebra, and

the base articulates with the body of the 5th

lumbar vertebra to form the lumbosacral joint.

Coccyx:- It is also formed by fusion of 4 coccygeal vertebrae

(Co1~Co4).

- They fuse between 20 and 30 years of age.

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- The dorsal surface of the body of coccyx two long coccygeal cornua that are connected by

ligaments to the sacral curnua.

- The coccygeal cornua are the pedicles and superior articular processes of the 1st

coccygeal

vertebra.

- On the lateral surfaces of coccyx are a series of transverse processes (the 1st

pair are the

largest).

- The coccyx articulates superiorly with the apex of the sacrum.

- In females, the coccyx points inferiorly and inmales, it points anteriorly.

Thorax:- It refers to entire chest.

- The skeletal portion of the thorax is a bony cageformed by the sternum, costal cartilages, ribs, and

the bodies of thoracic vertebrae.

- The thoracic cage is narrower at its superior end

and broader at its inferior end and flattened from

front to back.

Sternum (breastbone): - It is flat, narrow bone measuring about 15 cm in length, located on the anterior midline of

the thoracic wall.

- It consists of three portions:

• The manubrium, the superior portion.

• The body, the middle and largest portion.

• The xiphoid process, the inferior, smallest portion.

-

The sternal angle, the junction of manubrium and the body.- The manubrium has a depression on its superior surface called

the suprasternal notch.

- Lateral to suprasternal notch are clavicular notches thatarticulate with the medial ends of the clavicles to form

sternoclavicular jonts.

- The manubrium also articulates with the costal cartilages of the

1st

and 2nd

ribs to form the sternocostal jonts.

- The body of sternum articulates directly or indirectly with the

costal cartilages of the 2nd

to 10th

ribs.- The xiphoid process consists of hyaline cartilage during infancy

and childhood and does not ossify completely until a person is

about age 40.

- It has no ribs attached to it but it provides attachment for some

abdominal muscles.

- Incorrect hand position during CPR may result in a fracture of

the xiphoid process, deriving it into internal organs.

The Ribs:

- 12 pairs of ribs give structural support to the sides of the thoracic cavity.

- They increase in length from the 1st

to 7th

ribs, then decrease in length to the 12th

rib,

-



١٨

- - Each articulates posteriorly with its corresponding thoracic

vertebra.

- The 1st

to 7th

pairs of ribs have a direct anterior attachment to the

sternum by a strip of hyaline cartilage called costal cartilage.

- These ribs are called true (vertebrosternal) ribs.- The remaining 5 pairs of ribs called false ribs because their costal

cartilages either attach indirectly to sternum or do not attach to

sternum at all.

- The cartilages of the 8th

, 9th

, and 10th

pairs of ribs attach to eachother and then to the cartilages of the 7

thpairs of ribs.

- These false ribs are called vertebrochondral ribs.

- The 11th

and 12th

pairs of ribs called floating (vertebral) ribs,

because their anterior ends does not attach to the sternum at all but

attach only posteriorly to the thoracic vertebrae.

- The parts of typical ribs (3rd

to 9th

ribs): o The head is a projection at the posterior end of the rib; it consists of two facets that

articulate with the facets on the bodies of adjacent thoracic vertebrae to form

vertebrocostal joints.o The neck is a constricted portion just lateral to the head.

o A knoblike structure on the posterior surface where the neck joins the body is called a

tubercle.

o The non-articular part of tubercle affords attachment to the ligament of the tubercle, but

the articular part of tubercle articulates with the facet of a transverse process of the

inferior of the two vertebrae to which the head of the rib is connected (they also form

vertebrocostal joints).o The body (shaft) is the main part of the rib.

o A short distance beyond the tubercle, a big change in the curvature of the shaft occurs,this called the costal angle.

o The inner surface of the rib has a costal groove that protects blood vessels and small

nerve.

The 1st

rib:

-

The 1

st

rib is the shortest, broadest, and the most sharply curved of the ribs.- It is an important landmark because of its close relationship to the nerves of the brachial

plexus (provides the entire nerve supply of the shoulder and the upper limb), two major

blood vessels (subclavian artery and vein), and two skeletal muscles (anterior and medial

scalene muscles).

- The superior surface of it has two shallow grooves (one for subclavian vein and one for

subclavian artery + inferior trunk of the brachial plexus).

- The superior surface also is a point of attachment of anterior and middle scalene muscles.

The 2nd rib:- It is thinner, less curved, and longer than 1

strib.



٩

The 10th rib:- It has a single articular facet on its head.

The 11th and 12th ribs: - They have single articular facets on their heads, but no necks, no tubercles, and no costal

angles.

• The spaces between ribs, called intercostal spaces, are

occupied by intercostal muscles, blood vessels, and nerves.

• The structures passing between the thoracic cavity and the

neck pass through an opening called the superior thoracic

aperture (trachea, esophagus, nerves, and blood vessels that

supply and drain the head, neck, and upper limbs), isbordered by the 1

stthoracic vertebra (posteriorly), the first

pair of ribs and their cartilages, and the superior border of

manubrium of sternum (anteriorly).

• The structures passing between the thoracic cavity and abdominal cavity pass through

the inferior thoracic aperture, which is closed by the diaphragm, pass structures such

as esophagus, nerves, and large blood vessels.

- it is bordered by 12th

thoracic vertebra (posteriorly), the 11th

and 12th

pair of ribs, the

costal cartilages of ribs 7 to 10, and the joint between the body and xiphoid process of

sternum (anteriorly).

The End

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