Skull anatomy l General human anatomy (Head and neck) revision

 

Skull anatomy l Human anatomy (Head and neck) revision for dental students

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collection in skull anatomy

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Norma Lateralis
(Side View of Skull)

 

¦ It includes the following bones:

1. Temporal bone (All its parts except the petrous).
2. Lateral surface of greater wing of sphenoid.
3. Parietal.            
4. Zygomatic bone.       
5. Nasal bone.           
6. Maxillary bone.
7. Parts of frontal and occipital bones.
8. Lateral aspect of mandible .

¦ There are three fossae in the norma lateralis:

1.         Temporal fossa.
2.  Infratemporal fossa.
3. 3.     Pterygopalatine fossa.

¦ The norma lateralis shows the following features:

1-   SUPERIOR & INFERIOR TEMPORAL LINES : 

• inferior line becomes more prominent and become continuous with the supra-mastoid crest.

2-   ZYGOMATIC ARCH: 

• formed by the temporal process of zygomatic bone and zygomatic process of temporal bone

3-   EXTERNAL ACOUSTIC (AUDITORY) MEATUS: 

• It lies below the root of the zygomatic arch , its anteroinferior margin is formed by the tympanic part of temporal bone while its posterosuperior margin is formed by the squamous part of temporal bone.

4-   SUPRAMEATAL TRIANGLE: 

• A small triangule lies postero-superior to the external acoustic meatus . Bounded above by the supra-mastoid crest, in front by the postero-superior meatal margin and behind by a vertical line tangent to the posterior meatal margin. It forms the lateral wall of the mastoid antrum which is 1.5 cm deep to it.

5-      MASTOID PART OF TEMPORAL BONE:

•  The posterior part of the temporal bone which lies posterior to the external auditory meatus..
• The point of meeting of the parietal, occipital and mastoid bones is called Asterion  which at birth it is the site of mastoid fontanelle which ossifies and closes at the end of the 1^st year.
• The mastoid process is a nipple-like downward extension from the mastoid part of temporal bone.

6-   THE STYLOID PROCESS:

• extends from the lower part of the temporal bone. It lies anterior and medial to the mastoid process .

7-   TEMPORAL FOSSA: 

• The space between the temporal lines and the zygomatic arch.

@ Boundaries:
·         Above: superior temporal lines.
·         In front: Zygomatic bone and frontal process of zygomatic bone.
@ The anterior wall of temporal fossa is formed of temporal surface of zygomatic bone containing the zygomatico-temporal foramen for zygomatico-temporal nerve and vessels.
·         Behind: Supramastoid crest.
·         Below: Zygomatic arch (deep to it the temporal and infratemporal fossae communicate together).
·         Medially :
@ Parietal, frontal, squamous part of temporal and greater wing of sphenoid bone articulate together at pterion which is H-shaped suture .
@ Pterion  lies 4 cm above the midpoint of zygomatic arch & 4 cm behind the fronto-zygomatic suture.
@ It marks the anterior division of the middle meningeal artery which is liable to be torn in fracture of this area, resulting in extradural hematoma.
@ Pterion is the site of the sphenoidal  fontanelle which ossifies at about 3 months after birth.

8-   INFRATEMPORAL FOSSA: lies below the temporal fossa.

v  Boundaries:
1.     In front : Back of body of maxilla containing posterior superior alveolar foramen.
2.     Behind : styloid process.
3.     Medially : Lateral pterygoid plate.
4.     Laterally : Ramus of mandible.
5.     Above: Infratemporal surface of greater wing of sphenoid.
v  Communications:
1.     With temporal fossa through the gap deep to zygomatic arch.
2.     With pterygopalatine fossa through the pterygomaxillary fissure.
3.     With orbit through inferior orbital fissure.
4.     With middle cranial fossa through foramen ovale and foramen spinosum.
 

9-   PTERYGOPALATINE FOSSA: 

• A small space that lies below the apex of the orbit. It communicates laterally with the infratemporal fossa through the pterygomaxillary fissure.

Important points related to the skull

1. Nasion: Point at the root of the nose.
2. Glabella: Above nasion between 2 superciliary arches.
3. Bregma: Junction of coronal & sagittal sutures.
4. Vertex: Highest point of skull.
5. Lambda: Junction of sagittal & lambdoid suture.
6. Inion: Center of external occipital protuberance.
7. Pterion: Lies 3.5 cm behind and 1.5 cm above the fronto-zygomatic suture, it marks the anterior branch of middle meningeal artery.
8. Asterion: Lies at the junction of parietal, occipital and mastoid part of temporal-bone, it marks the highest point of transverse sinus. -

Skull of the newly born

1. The face  & cranium ratio is 1/8 as compared to Y2 in the adult.
2. This is due to small maxillary bones, maxillary sinuses, nasal cavity and non-eruption of teeth.
3. The frontal and parietal eminences are well apparent.
4. The glabella, superciliary arches and mastoid processes are not well developed.
5. There is a frontal metopic suture: Closes at 2-8 years. It exists in skull of (black races) Negroes.
6. Orbital cavities are relatively large.
7. Internal & middle ears and mastoid antrum are almost adult in size.
8. Mandible at birth has 2 halves, mental foramen near upper border & angle was obtuse.

Ossification of skull bones is not complete as a result of presence of six fontanelles:

1. Anterior fontanelle , the largest, It is diamond-shaped measuring 4 cm in its anteroposterior diameter and 2.S cm in the transverse diameter. It closes at 18 months at bregma.
2. Posterior fontanelle , is triangular in shape and is situated at junction of sagittal and lambdoid sutures. It closes at (birth-3 months) at the lambda.
3. 2 sphenoid fontanelles , close at 3 months at the pterion.
4. 2 mastoid fontanelles, close at end of the 1^st year at the asterion. Importance of fontanelles:

• Determination of position during delivery.
• Delayed closure fontanelles (in rickets).
• Bulging fontanelles occur if the intracranial pressure increases.
• Depressed fontanelles occur in dehydration.
• S. Anterior fontanelle may be used for injection of fluids or blood in SSS.

Sex differences of the skull

• Till puberty, there are little differences between the skulls of the two sexes, but female skull is:

1. Smaller (small paranasal sinuses).
2. Lighter in weight.
3. More smooth with less prominent bony ridges (e.g. superciliary arches, glabella, nuchal lines & ext. occipital protuberance).
4. The mastoid processes and occipital condyles are smaller.

Applied anatomy of the skull

• Fracture of the skull base at the anterior cranial fossa ~ leakage of CSF & blood from the nose.
• Fracture of the skull base at the middle cranial fossa ~ leakage of CSF & blood from external auditory meatus & 7th and 8th cranial nerves injury.
• Fracture of the skull base at the posterior cranial fossa ~ leakage of blood from back of the neck due to injury of sigmoid sinus.
• Foramina and Structures Passing Through in Skull

Foramina and Structures Passing Through Norma Verticalis & Occipitalis

Parietal emissary Foramen :       

• Parietal emissary vein. (from scalp to superior sagittal sinus)

Mastoid emissary foramen: .      

• Mastoid emissary vein.

 

Foramina and Structures Passing Through 

Norma Frontalis & Lateralis

Supratrochlear notch or Foramen : .     

• Supratrochlear nerve and vessels.

Supraorbital notch or foramen :

• Supraorbital nerve and vessels.

Zygomaticofacial foramen :.      

• Zygomaticofacial nerve and vessels.

Zygomaticotemporal foramen:.  

• Zygomaticotemporal nerve and vessels.

Inferior orbital fissure     

1. Infraorbital (maxillary) Nerve. & Vein.                  
2. Zygomatic Nerve . &vein .
3. Orbital nerves to sphenopalatine ganglion.
4. Communicating veins between ophthalmic veins & pterygoid venous plexus.

Pterygo-maxillarv fissure: .       

• Maxillary Nerve. & Vein.

Posterior superior alveolar foramen:    

• Posterior superior alveolar Nerve. & vein.

 

Foramina and Structures Passing Through Norma Basalis Interna

Foramen caecum:  

• Emissary vein

Cribriform plate of the ethmoid.:

1. Olfactory (I) nerve.
2. Anterior ethmoidal nerve and vessels.

Optic canal :

1. Optic (II) nerve.                
2. Ophthalmic artery.

Superior orbital fissure.    

Nerves:

1. Lacrimal Nerves .      
2. Frontal Nerves .     
3. Trochlear Nerves
4. Superior division of oculomotor Nerves
5. Nasociliary Nerves.
6. Inferior divisions of oculomotor nerve.
7. Abducent nerve.

Two Ophthalmic veins Recurrent branch of lacrimal A.

Foramen rotundum:         

• Maxillary branch of the trigeminal nerve.

Internal auditory meatus:

1. Facial (VII) and auditory (VIII) nerves.
2. Internal auditory br. of basilar artery.

Foramina and Structures Passing Through Norma Basalis Externa

Greater palatine Foramen:

• Greater palatine nerve and vessels

Lesser palatine foramen :.

• Lesser palatine nerves and vessels

2 lateral foramina:.

• Greater palatine vessels.

2 median formina: 

• Right and left nasopalatine nerves

Foramen ovale :

1. Main trunk of mandibular nerve.              
2. Motor toot of trigeminal nerve.
3. Middle meningeal vein.                      
4. Accessory meningeal artery.
5. Lesser superficial petrosal nerve.          
6. Emissary vein.

Foramen spinosum :        

1. Nervus spinosus.                                                   
2. Middle meningeal artery.

Foramen lacerum : 

1. Meningeal br. of ascending pharyngeal- A.          
2. Emissary vein.

Carotid canal :

1. I.C.A. & sympathetic plexus.                   
2. Deep petrosal nerve.
3. Emissary vein.

Jugular foramen:

•             Anterior medial compart:         Inferior petrosal venous sinus.
•             Middle compart :         IX, X, XI cranial nerves.
•             Posterolateral  compart:           End of sigmoid sinus and beginning of I.JV.

Stylomastoid foramen.     

1. Facial (VII) nerve.
2. Stylomastoid branch of occipital or post. auricular artery.

Hypoglossal canal. 

1. Hypoglossal (XII) nerve.                            
2. Emissary vein.

Foramen magnum.  

Nervous structures:   

1. Medulla oblongata.
2. Spinal accessory nerves.                 
3. Tonsils of cerebellum
4. Sympathetic plexus around arteries

Vessels:       

1. Anterior and posterior spinal arteries.
2. Vertebral plexus of vein.

Ligaments: Apical & vertical limb of cruciate ligaments Membrana tectoria.

Meninges: pia, arachnoid & dura maters.

Pterygomaxillary canal:

• Maxillary artery & nerve

Tympanomastoid Fissure:

• Auricular branch of vagus nerve.