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Term Paper on Human Skull
Term Paper # 1.
Anatomical Structure of Human Skull:
It forms the skeleton of head and includes the mandible. The skull without mandible is called cranium. It has a large cranial cavity inside containing brain with its meninges, blood vessels and cranial nerves.
Skull is made-up of 22 bones + 6 ear ossicles and is divided into:
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(a) Neurocranium or Calvaria:
It consists of 8 bones:
(i) Paired bones- Parietal and temporal.
(ii) Unpaired bones- Frontal, occipital, sphenoid and ethmoid.
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(b) Facial Skeleton:
It consists of 14 bones:
(i) Paired bones- Maxilla, zygomatic, nasal, lacrimal, palatine and inferior nasal concha.
(ii) Unpaired bones- Mandible and vomer.
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Anatomical Position of Skull:
1. Orbital cavities are directed forwards.
2. Lower margins of the orbits and upper margins of external acoustic meatuses should be in the same horizontal plane (Frankfurt’s plane).
Term Paper # 2.
External Features of the Skull:
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It is studied in five different views:
1. Superior view or norma verticalis
2. Posterior view or norma occipitalis
3. Anterior view or norma frontalis
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4. Lateral view or norma lateralis
5. Inferior view or norma basalis.
1. Norma Verticalis:
Skull appears oval and wider posteriorly than anteriorly. Four bones participating in its formation – frontal anteriorly, two parietals – one on each side and one occipital bone posteriorly.
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These bones are united by three sutures:
(a) Coronal Suture:
Lies between the frontal and the two parietal bones.
(b) Sagittal Suture:
Lies between the two parietal bones.
(c) Lambdoid Suture:
Lies between the two parietal bones and occipital bone.
Metopic Suture:
This is present in 3 to 8% cases and is seen between the two halves of the frontal bones.
Other features are:
(a) Bregma:
It is the point at which coronal and sagittal sutures meet.
(b) Parietal Eminence:
It is the area of maximum convexity of parietal bone.
(c) Vertex:
It is the highest point of the skull and lies near the middle of the sagittal suture.
(d) Parietal Foramen:
A small foramen is present on each parietal bone near the sagittal suture about 3 cm in front of lambda.
(e) Temporal Lines:
Begin at the posterior border of zygomatic process of the frontal bone and arch backwards and upwards over the parietal bone and further divides into superior and inferior temporal lines. Superior line fades backwards but inferior continues downwards and forwards to become continuous with the supramastoid crest.
2. Norma Occipitalis:
It consists of posterior part of parietal bones; occipital bone and mastoid part of temporal bones present infero laterally, one on each side.
Features:
i. Lambdoid Suture:
It lies between the occipital bone and the two parietal bones.
ii. Occipitomastoid Suture:
Is present between the occipital bone and the mastoid part of temporal bone.
iii. Parietomastoid Suture:
It lies on each side between parietal bone and the mastoid part of temporal bone.
iv. Lambda:
Is the point at which sagittal and lambdoid sutures meet.
v. External Occipital Protuberance:
It is the median bony projection, midway between the lambda and foramen magnum.
vi. Inion:
It is the most prominent point of external occipital protuberance.
vii. Superior Nuchal Lines:
These are curved bony ridges passing laterally on each side from external occipital protuberance.
viii. Highest Nuchal Lines:
In some cases a curved, faint bony ridge is seen 1 cm above the superior nuchal lines.
ix. External Occipital Crest:
It is a median vertical ridge passing downwards from the external occipital protuberance to the posterior margin of foramen magnum.
x. Inferior Nuchal Lines:
These are curved bony ridges passing laterally on each side from the middle of external occipital crest.
3. Norma Frontalis:
It is the front view of skull – oval in shape, wider above and narrows below.
Bones forming this view are:
a. Frontal bone forms forehead.
b. Right and left nasal bones form bridge of nose.
c. Right and left maxillae form upper jaw.
d. Right and left zygomatic bones form cheek prominences.
e. Mandible forms lower jaw.
Characteristic features are divided into:
A. In the Median Region:
a. Glabella:
Is a median elevation between the super ciliary arches above the nasion.
b. Nasion:
Is the meeting point of internasal and frontonasal sutures.
c. Anterior Nasal Spine:
It is a sharp bony projection in the median plane below the anterior nasal aperture.
d. Symphysis Menti:
Is a median ridge joining the two halves of the mandible.
e. Mental Protuberance:
Lower end of symphysis menti ends in a triangular elevation called mental protuberance.
f. Gnathion:
Is the middle point at the base of mandible.
B. In the Lateral Region:
From above downwards:
a. Frontal Prominence:
Is a rounded elevation above the super ciliary arch?
b. Three Foramen Lying in Same Vertical Plane:
(i) Supra orbital notch or foramen
(ii) Infra orbital foramen
(iii) Mental foramen.
c. Oblique Line on Body of Mandible:
Extending from below the lower end of anterior border of ramus of mandible to the mental tubercle.
4. Norma Lateralis:
Lateral aspect of skull shows following features:
a. Above – bones from anterior to posterior are nasal, frontal, parietal and occipital.
b. In middle – bones are maxilla, zygomatic, sphenoid and temporal.
c. Below – Body and ramus of mandible.
Sutures:
They are:
a. Coronal suture.
b. Parieto – squamosal suture – between parietal and squamous part of temporal bone.
c. Parieto mastoid suture – between parietal and mastoid part of temporal bone.
d. Occipitomastoid suture – between occipital and mastoid part of temporal bone.
e. Lambdoid suture.
Characteristic features are:
a. Temporal Lines:
Superior and inferior temporal lines.
b. Zygomatic Arch:
Is formed by union of temporal process zygomatic bone and zygomatic process of temporal bone.
c. External Acoustic Meatus:
Lies just below the posterior root of zygoma.
d. Suprameatal Triangle of Macewen:
Is a small triangular depression lies postero-superior to external auditory meatus, bounded by:
i. Superiorly – Supramastoid crest.
ii. Anteriorly – Postero superior margin of external acoustic meatus.
iii. Posteriorly – A vertical line passing through posterior margin of meatus.
iv. Aditus-ad-antrum lies 12 mm deep to this triangle in adults.
e. Mastoid Process:
Behind the meatus part of temporal bone projecting downwards.
f. Asterion:
Is the meeting point of parietomastoid, occipitomastoid and lambdoid sutures. In infant it is the site of postero lateral fontanelle.
g. Styloid Process:
A thin long bony process projecting downwards, medially and forwards from the temporal bone. Its base is ensheathed by the tympanic plate of temporal bone.
h. Temporal Fossa:
Is the depressed area bounded above by temporal line and below by zygomatic arch laterally and infratemporal crest of sphenoid medially.
i. Pterion:
Lies in the anterior part of the temporal fossa, where four bones meet at an ‘H’ shaped suture – frontal, parietal, temporal and greater wing of sphenoid. It is situated 4 cm above the mid-point of the zygomatic arch. Internally it is related to middle meningeal vessels.
j. Infra Temporal Fossa:
Lies on the side of the skull below the zygomatic arch, bounded by lateral pterygoid plate medially and by ramus of mandible laterally.
5. Norma Basalis:
Inferior aspect of skull externally studied by dividing it into three parts – anterior, middle and posterior part.
(I) Anterior Part:
Formed by alveolar arch and hard palate.
Features are:
(a) Alveolar Arch:
Formed by maxilla, bears sockets for roots of upper teeth.
(b) Hard Palate:
Is formed by palatine process of maxilla – anterior 3/4th and by horizontal plates of palatine bones – posterior 1/4th.
It has following features:
(i) Incissive Fossa:
Present anteriorly in the median plane behind the incisor teeth. Two (right and left) incissive foramina pierce the wall of the fossa.
(ii) Greater Palatine Foramen:
One on each side, lies postero laterally, medial to last molar tooth.
(iii) Lesser Palatine Foramina:
Usually two in number lies behind the greater palatine foramen.
(iv) Posterior Nasal Spine:
A conical bony projection in the median plane on the sharp free posterior border of hard palate.
(II) Features in the Middle Part:
It lies behind the hard palate upto a line passing through the anterior margin of foramen magnum transversely.
(A) Median Area Presents:
(i) Posterior border of vomer separating two posterior nasal apertures.
(ii) A broad bar of bone formed by fusion of body of sphenoid and basilar part of occipital bone. In the centre of basiocciput a bony elevation is seen called pharyngeal tubercle.
(B) Lateral Area Presents:
(i) Pterygoid Process:
Projecting downwards from sphenoid bone behind last molar tooth. It divides into medial and lateral pterygoid plates, separated by pterygoid fossa. Each plate has a posterior free border. Upper end of posterior border of medial pterygoid plate encloses a triangular boat shaped depression called scaphoid fossa, lower end bears a hook-like process called pterygoid hamulus.
(ii) Infra Temporal Surface of Greater Wing of Sphenoid:
It lies lateral to pterygoid process and presents with four margins and four foramina.
Margins are:
(a) Anterior Margin:
Forms posterior margin of inferior orbital fissure.
(b) Anterolateral Margin:
Forms infratemporal Crest.
(c) Posterolateral Margin:
Articulates with the squamous part of temporal bone.
(d) Postero Medial Margin:
Articulates with petrous part of temporal bone.
Foramina:
All located along the posteromedial margin are:
(a) Foramen Spinosum:
A small circular foramen at the base of spine of sphenoid.
(b) Foramen Ovale:
Large oval foramen lies medial to foramen spinosum.
(c) Emissary Sphenoidal Foramen of Vesalius:
A small foramen sometimes present between foramen ovale and scaphoid fossa.
(d) Canaliculus Innominatus:
Occasionally present lies between foramen ovale and foramen spinosum.
(iii) Spine of Sphenoid:
Between the postero medial and postero lateral margins of the greater wing of sphenoid a small conical bony projection is present called spine of sphenoid. Two nerves are related to it – auriculo temporal nerve lies laterally and chorda tympani nerve lies medial to spine.
(iv) Sulcus Tubae:
Is a groove between postero lateral margin of greater wing and petrous temporal bone? It lodges cartilaginous part of the auditory tube.
(v) Inferior Surface of Petrous Temporal Bone:
Is triangular in shape. The apex is directed medially and anteriorly, forms the posterior part of foramen lacerum on articulating with sphenoid. In this part opening of carotid canal is seen.
(vi) Tympanic Part of Temporal Bone:
It lies lateral to petrous part and joins with squamous part above at squamotympanic suture.
(vii) Squamous Part of Temporal Bone:
Mandibular fossa is present behind the anterior root of zygomatic process and the squamous part contributes to articular part of fossa.
(viii) Tegmen Tympani:
Is a thin plate of bone, arises from anterior surface of petrous temporal part – divide the squamotympanic suture into two parts – petrotympanic and petrosquamous.
(III) Features in the Posterior Part:
(a) Median Area:
Presents from before backwards:
(i) Foramen magnum,
(ii) External occipital crest and
(iii) External occipital protuberance.
(b) Lateral Area:
Presents on each side.
(i) Occipital Condyle:
It is oval having convex articular surface lies on the side of foramen magnum.
(ii) Hypoglossal Canal:
Lies anterosuperiorly to occipital condyle.
(iii) Condylar Fossa:
Lies behind the occipital condyle, sometimes it has a canal – called condylar canal.
(iv) Jugular Process of Occipital Bone:
Lies lateral to occipital condyle and forms posterior boundary of jugular foramen.
(v) Squamous part of occipital bone.
(vi) Jugular Foramen:
It is a large elongated foramen at posterior end of petro occipital suture. Its anterior wall is hollowed out to form jugular fossa.
(vii) Petrous Temporal Bone:
Shows tympanic canaliculus lies between jugular fossa and carotid canal.
(viii) Styloid Process:
Projecting downwards between petrous and tympanic part is the posterior aspect.
(ix) Stylomastoid Foramen:
Situated between styloid and mastoid process of temporal bone.
(x) Mastoid Process:
Projecting downwards laterally from temporal bone.
Term Paper # 3
. Functions of Human Skull:
1. It protects the brain and meninges.
2. Lodges eye, ear, nose and tongue (organs of special senses).
3. It lodges masticatory apparatus and upper digestive tracts.
4. Upper part of respiratory system is found within it.
Cranial Capacity:
i. It gives an idea about the approximate volume of the brain.
ii. Average capacity in normal adult – 1350 – 1400 cc.
iii. In female 10% less than male.
iv. Microcephalic – capacity below – 1350 cc.
v. Megacephalic – capacity above – 1450 cc.
vi. The normal skull is mesocephalic.
Neonatal Skull:
Have the following parts:
1. Vault
2. Face
3. Base.
The vault of the foetal skull is formed by a pair of frontal, a pair of parietal, occipital, a pair of temporal and greater wings of sphenoid bone. There are membrane filled areas in between these bones – called fontenelles. At the time of birth six fontenelles are present. The two frontal bones are separated by the metopic suture.
Anterior Fontenelle:
It is lozenge shaped, situated at the junction of coronal and sagittal sutures. It is the junction of four bones – a pair of frontal and parietal bones. The pulsation of the cerebral arteries can be felt on the surface of the fontenelle.
Term Paper # 4.
Clinical Importance of Human Skull:
1. Vertex presentation of foetal head can be diagnosed during pregnancy.
2. Intra cranial pressure can be juged by palpating this fontenelle. Child is well nourished or not, can be diagnosed.
3. Age of the child can be determined – above or below two years.
4. Blood samples can be obtained from the superior sagittal sinus via anterior fontenelle.
By the age of 18 months the fontenelles are replaced by bone and represented by bony points.
The site of fontenelles are:
A pair of antero lateral fontenelles – Pterion.
A pair of postero lateral fontenelles – Asterion.
The fontenelles help moulding of the foetal head during childbirth.
The mandible is bifid and united by fibrous tissue, angle of mandible is obtuse. The coronoid process extends to a higher level than condylar process.
The mastoid process is not developed at the time of birth but mastoid air sinus is well developed. Facial nerve is superficial and liable to be injured during forcep’s delivery.
Styloid process is cartilagenous and zygomatic process is not articulating with the zygomatic bone.