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OSTEOLOGY OF HEAD AND NECK NOTES



SUPERIOR ORBITAL FISSURE   (SE) 

Superior orbital fissure is an elongated fissure that transmits vessels and nerves to and from the orbit.
It is divided by common tendinous ring into three parts- lateral, middle and medial.
Structures passing through superior orbital fissure
Lateral part
Lacrimal nerve  Frontal nerve  trochlear nerve
Superior ophthalmic vein
Middle part
Upper and lower divisions of occulomotor nerve,  nasociliary nerve abducent nerve
Medial part
Inferior ophthalmic vein

HYOID BONE    (SE)

Hyoid bone is “U” shaped bone in the upper part of neck. It is suspended by muscles and ligaments. It has body, lesser cornu, and greater cornu.
Body 
          It is the central thickend part. 
Attachments 
        Geniohyoid and mylohyoid , omohyoid, thyrohyoid and genioglossus muscles.
Lesser cornu  
        Small projection at the junction of body and greater cornu.
Attachments
        Stylohyoid ligament and part of middle constrictor
Greater cornu
        Projects posterolaterally from the body and ends in a tubercle.
Attachments 
         Hyoglossus and middle constrictor
Development of hyoid bone
Upper part of body and lesser cornua  develop from 2nd branchial arch mesenchyme
Lower part of body and greater cornua develop from 3rd branchial arch mesenchyme  PAIRED CRANIAL BONES (SA)
In the adult paired cranial bones are  
Parietal , temporal,maxillae, zygomatic bones,ethmoid,lacrimal, palatine, nasal and inferior conchae.

ANTERIOR FONTANELLE   (SA)

Anterior fontanelle) of the fetal or infant skull comprises of a diamond shaped   soft membranous gap between the frontal and parietal bones at the junction of coronal and sagittal suture.                                                                                                              
Fontanelles allow for rapid stretching and deformation of the cranium as the brain expands faster than the surrounding bone can grow.
Anterior fontanelle close between 9months to1/12 years after birth

Clinical importance

          A very tense or bulging anterior fontanelle indicates raised intracranial pressure           eg hydrocephalus.
        A sunken (also called "depressed") fontanel indicates dehydration or malnutrition.
        Fontanelles allow the infant brain to be imaged using ultrasonography
         Premature complete ossification of the sutures is called craniosynostosis.

ASTERION   (SA)

The point on the surface of the skull where the lambdoid, parietomastoid, and   occipitomastoid sutures meet is known as asterion 
The asterion has become important in neurosurgery. Surgeons use it as a measurement for safe entrance into the skull during operations, such as the removal of tumors like meningiomas. 
Another common operation is for treating stenosis, or narrowing, of the lambdoid suture.

PTERION   (SA)

 The pterion is located on the side of the skull, just behind the temple. It is the junction between four bones:
The parietal bone
The squamous part of temporal bone
The greater wing of sphenoid bone  
The frontal bone  




Clinical importance
            The pterion is known as the weakest part of the skull.
     The anterior division of the middle meningeal artery runs underneath the            pterion. Consequently, a traumatic blow to the pterion may rupture the middle           meningeal artery causing an epidural haematoma. 
     The pterion may also be fractured indirectly by blows to the top or back of the            head that place sufficient force on the skull to fracture the pterion.

ATTACHMENTS OF MASTOID PROCESS (SA)

Mastoid  process is a rounded downward projection of the temporal bone. Its medial part is notched called mastoid notch.
Attachments
Sternomastoid
Splenius capitis
Longissimus capitis
Posterior belly of digastric muscle at the mastoid notch.

BREGMA (SA)

Bregma is the anatomical point on the skull at which the coronal suture is intersected perpendicularly by the sagittal suture.
 Development
The bregma is known as the anterior fontanelle during infancy. The anterior fontanelle is membranous and closes in the first 36 months of life.
Clinical Significance
In the congenital disorder cleidocranial dysostosis, the anterior fontanelle never closes to form the bregma.
The bregma is often used as a reference point for stereotactic surgery of the brain.
Also, examination of an infant includes palpating the anterior fontanelle.
A sunken fontanelle indicates dehydration, whereas a very tense or bulging anterior fontanelle indicates raised intracranial pressure.

BONES OF HARD PALATE  (SA)

Hard palate is a partition between nasal and oral cavities.
Anterior 2/3rd is formed by palatine processes of maxillae
Posterior 1/3rd is formed by the horizontal processes of palatine bone. 

FETAL SKULLL (SA)

In the fetal skull the cranium is proportionately larger than the facial skeleton.
Characteristic features Fontanellae         there are 6 fontanellae present at the angles of parietal bones. Anterior     fontanelle is most prominent.
Mastoid process 
                         Not developed until the 2nd year. Facial nerve lies in a superficial plane.

Paranasal air sinuses

          Frontal air sinus is absent at birth. Maxillary air sinus is rudimentary.       Mandible and frontal bones are separated by sutures in the midline.

LIGAMENTS   OF ATLAS (SA)

The atlas has an anterior arch and posterior arch with anterior and posterior tubercles. The lateral masses posses superior and inferior articular processes and transverse processes
Attachments 
Anterior tubercle
          Anterior longitudinal ligament Posterior tubercle
                          ligamentum nuchae
Tubercle on lateral mass
                         Transverse ligament of atlas
Upper border of anterior arch
                         Anterior atlanto-occipital membrane
Upper border of posterior arch
                         Posterior atlanto-occipital membrane

FORAMINA IN CRANIAL FOSSAE (SA)

Foramina in anterior cranial fossa
Cribriform plate of ethmoid bone
Optic nerve
Middle cranial fossa
Superior orbital foramen
Foramen rotundum  Foramen  ovale
Foramen spinosum 
         Foramen lacerum
Posterior cranial fossa
Internal auditory meatus
Jugular foramen
Hypoglossal canal 
Foramen magnum
Mastoid  foramen





 




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