Anterior cranial fossa >Middle cranial fossa > Posterior cranial fossa
The inside view of cranium is known as cranial cavity.
Contents of cranial cavity:
The cranial cavity contains the brain, pineal and hypophysis cerebri, parts of the cranial and spinal nerves, blood vessels, meninges and cerebrospinal fluid.
Bones that make up the cranial cavity:
Cranial cavity is contained by the frontal, parietal, sphenoid, temporal and occipital bones, and in part the ethmoid, all lines by fibrous endocranium, external zone of dura mater and pericranium.
Importance of cranial cavity:
Cranial cavity forms the floor of brain, while the roof of brain is formed by skull cap or calvaria.
Divisions of cranial cavity:
The cranial cavity is divided into three cranial fossa.
- Anterior cranial fossa which accommodates the anterior lobe of brain.
- Middle cranial fossa, much wider than the anterior cranial fossa contain the 2 temporal lobes of brain.
- Posterior cranial fossa is much shallower and wider than the middle cranial fossa and it accommodates the occipital lobes of the brain.
Anterior cranial fossa:
Interiorly it contains sphenoid bone.
Sphenoid bone consists of three parts
b) -Lesser wings, 2 in number
c) -Greater wing, also 2 in number
Body of sphenoid is again subdivided into anterior, middle and posterior parts.
Anterior part lies in anterior cranial fossa, middle in middle cranial fossa and posterior in posterior cranial fossa. So sphenoid bone is common in all three fossae.
Boundaries and foramens of anterior cranial fossa:
Anteriorly and laterally is bounded by frontal bone
The floor of anterior crania fossa id formed by orbital plate of frontal bone, ethmiod cribriform plate , anterior border of sphenoid’s lesser wings and anterior part of the body.
Bounded by posterior border of lesser wing of sphenoid, anterior clinoid process and sulcus chiasmaticus.
Ethmoid is present in the centre of cranial fossa and it forms part of its floor. It forms 4 sutures, 3 with frontal and 1 with sphenoid.
It is a sharp upward projection of ethmoid bone in the midline, for the attachment of falx cerebri.
Between the crista galli and the crest of the frontal bone is small aperture, the foramen cecum. In 85 % of the subjects, it is closed. While in 15% subjects, it is patent or open for the passage of vein of nose which drains into superior sagittal sinus.
Importance of foramen cecum is that the infection can travel easily from the nose to the venous sinus of the brain.
Cribriform plate of the ethmoid:
This is thee perforated part of the ethmoid. The upper surface of the cribriform plate supports the olfactory bulbs, and the small perforations in the cribriform plate are for the olfactory nerves.
Clinical importance: If cribriform plate is injured, then there will be loss of sensation of smell.
Anterior and posterior Ethmoidal canals:
There are 2 anterior Ethmoidal canals on the sides of upper surface of ethmoid for the passage of anterior Ethmoidal vessels and nerves. While posterior Ethmoidal canals give passage to post Ethmoidal vessels only.
Clinical importance of orbital plate of frontal bone:
Orbital part of frontal born not only forms the floor of anterior cranial fossa but also the roof of the orbit. If injury occurs to this plate, then bleeding from eyes could occur.