Cranial walls

The external surface of the skull presents the anterior and posterior wall, the paired lateral wall, the calvaria  and the external cranial base. Inside the skull there is the internal cranial base.

The superior wall of the skullis formed by the:

  • Squamous part of the frontal bone.
  • Two parietal bones.
  • Squamous part of the occipital bone.

There are some important landmarks of the neurocranium. At the superior aspect of the skullthe following anthropological points can be identified:

  • Bregma is a point where saggital and frontal (coronal) sutures join together.
  • Vertex is the highest point of the skull in the anatomical position. It is situated between the parietal bones in the median sagittal plane of the skull.
  • Occiput is the posterior part of superior wall of the skull.

Clinical comments

The fractures of the vertex area may cause the thrombosis of the superior sagittal sinus. During injury the arachnoid granulations are destroyed. They drains the cerebrospinal fluid into the venous sinus and increase the intracranial pressure. Decreasing the pressure or lumbar puncture is the treatment.

The anterior cranial wallis formed by:

  • Frontal bone
  • Two nasal bones
  • Two zygomatic bones
  • Two maxillas
  • Mandible.

At the anterioror frontal aspect of the skullthe following areas and anthropological points can be identified:

  • Forehead is the area located in the superior part of the anterior cranial wall
  • Nasion is located in the middle of frontonasal suture
  • Gnathion is the most inferior point of the inferior border of the mandible in the middline
  • Glabella is the elevation on the frontal bone. It is situated in the median sagittal plane crossing the line con necting the two superciliary arches.

The two apertures of extracranial cavities are present on the anterior cranial aspect of the skull:

  • Orbit aperture (orbita)
  • Anterior nasal cavity aperture (cavitas nasalis).

The anterior nasal cavity aperture or piriform aperture is present in the macerated skull. It is the foramen limited by the nasal bones and maxillae.

The orbit aperture is formed by the:

  • Frontal bone
  • Zygomatic bone
  • Maxilla.

The posterior cranial wallis formed by:

  • Squamous part of occipital bone
  • Two parietal bones
  • Petrous parts of temporal bones.

At the posterior aspect of the skullthe following anthropological points can be identified:

  • Inion is the most prominent projecting point of the external surface of the occipital bone. It lies in the midline on the level of the external occipital protuberance. Usually, it is bigger in males.
  • Lambda is an area where saggital and lambdoid sutures join together.

The lateral cranial wallis formed by the:

  • Frontal bone    
  • Parietal bone   
  • Occipital bone 
  • Temporal bone
  • Greater wing of sphenoid bone
  • Zygomatic bone
  • Maxillla

At the lateral aspect of the skull we can identify the following areas and anthropological points:

  • Pterion is a place where the frontal bone connects with the parietal, temporal (squamous part) and the sphenoid  (greater wing) bones around 4 cm above the midpoint of the zygomatic arch. It is a very important landmark for localization of the anterior branch of the middle meningeal artery.
  • Asterion is a craniometric point at the junction of the occipital, parietal and temporal bones.
  • Gonion is the craniometric point on either side at the angle of the mandible.

There are two extracranial fossae on the lateral cranial aspect of the skull:

  • Temporal fossa (fossa temporalis)
  • Infratemporal fossa (fossa infratemporalis).

Clinical comments

On the level of the pterion lies the anterior branch of the middle meningeal artery. The bone here is very thin and could fracture following a direct hit by an extradural hematomasuch as a golf ball. The fracture injury also could lacerated this artery.

The external surface of the cranial baseis formed by the:

  • Mandible
  • Alveolar processes of maxillae
  • Palatine processes of maxillae
  • Zygomatic bones
  • Zygomatic arches
  • Temporal bones
  • Occipital bone.

At the external surface of the cranial basethe following anthropological points can be identified:

  • Basion which is the middle point of the anterior margin of the foramen magnum.
  • Opisthion which is the middle point of the posterior margin of the foramen magnum.

The internal surface of the skull basepresents the triple-tiered floor of the cranial cavity. Each tier is called a fossa and these fossae are named from the front to the back as follows:

  • Anterior cranial fossa (fossa crani anterior)which is the highest one.
  • Middle cranial fossa (fossa crani medialis).
  • Posterior cranial fossa (fossa crani posterior)which is the lowest one.