Skull base and vault By Dr.Safa Ahmed Rheumatologist (MSc.) Skull base • This represents the floor of the cranial cavity on which the brain lies. Bones of the base of the skull • 5 bones compose the base of skull: 1. Frontal bone 2. Temporal bones 3. Occipital bone 4. Sphenoid bone 5. Ethmoid bone Cranial fossa • It is formed by the floor of the cranial cavity. • It is divided into 3 distinct parts: 1. Anterior cranial fossa 2. Middle cranial fossa 3. Posterior cranial fossa Anterior cranial fossa • Formed by the following bones: 1. Orbital plate of frontal bone 2. Cribriform plate of ethmoid bone 3. Small wings and part of the body of sphenoid bone. Contents: frontal lobes of the brain. Middle cranial fossa • It is deeper than the anterior fossa. • Formed by parts of the sphenoid and temporal bones. • Contents: temporal lobes and sella turcica on which the pituitary gland lies. Posterior cranial fossa • It is the most inferior of the fossae • Mainly formed by the occipital bone. • Contents: cerebellum, medulla, pons. foramen magnum internal acoustic meatus Foramina in the base of skull • Foramen ceacum • Optic foramen: transmit the optic nerve and ophthalmic artery into orbit. • Foramen magnum: is an oval shaped foramen in the base of the skull that transmits the spinal cord as it exits the cranial cavity. • Foramen ovale: lies in the sphenoid greater wing and transmits several nerves. • Jugular foramen: transmit the cranial nerves (9th, 10th,11th) and internal jugular vein. • Internal auditory meatus: provide a passage for the 7th and 8th cranial nerves and artery to the inner ear. • Other foramina: mastoid foramen, foramen spinosum, foramen rotundum and foramen lacerum. • These foramina transmit the cranial nerves( 12 cranial nerves). Vault of the skull • Bones of the vault: 1. Frontal bone 2. Parietal bones 3. Occipital bone 4. Temporal bones 5. Greater wings of sphenoid bone • It provides protection to the brain. • At birth these bones are not tightly bound to each other to allow passage of the head of the newborn through the birth canal. • Openings in the vault called the fontanells: anterior and posterior. The anterior fontanelle remains open up to 2 years after birth while the posterior fontanelle ossifies within 6-8 months after birth. • Fractures in the vault affect mainly the parietal and frontal bones. .