Skull

For symbolic or mythic uses of the human skull, see Skull (symbolism).

A skull, or cranium, is a bony structure which serves as the general framework for a head. The skull attempts to protect the brain, acting as a form of natural helmet.

Table of contents

1 Humans
2 Bones of the human skull

2.1 Cranial bones
2.2 Facial bones
2.3 Ear ossicles
2.4 Wormian bones
2.5 Foramina of skull base

3 See also

Humans

In humans, the skull is the uppermost portion of the human skeleton. It is made up of a number of bony parts—8 in the skull proper (neurocranium) and 14 in the facial area (splanchnocranium). There are five main skull sections—one occipital, two frontal, two parietal. The sections are fused together in adults along sutures—metopic, coronal, sagittal and lambdoid. At birth these sutures are fibrous and moveable, necessary for birth and later growth. At the points where sutures meet are fontanelles, the main ones are the anterior and posterior. The posterior fontanelle usually closes by eight weeks but the anterior fontanelle can remain up to eighteen months. The anterior fontanelle is located at the junction of the frontal and parietal bones, it is a "soft spot" on a baby's forehead. Careful observation will show that you can count a baby's heartrate by observing his or her pulse pulsing softly through the anterior fontanelle. If the brain is bruised or injured it can be extremely serious. Normally the skull protects the brain from damage through its hard unyieldingness, but in some cases of head injury, there can be raised intracranial pressure through mechanisms such as a subdural haematoma. In these cases the raised intracranial pressure can cause herniation of the brain out of the foramen magnum ('coning') because there is no space for the brain to expand to—this can result in significant brain damage or death unless an urgent operation is performed to relieve the pressure. This is why patients with concussion must be watched extremely carefully. In earlier times, a skull operation called trepanation was often performed for semi-mystical reasons and not only as an attempted life-saving technique. The skull also contains the sinus cavities. The meninges are the membranes that separate the brain from the skull.

Bones of the human skull

Wormian bones

\nIn addition to the usual centers of ossification of the cranium, others may occur, giving rise to irregular isolated bones termed sutural or Wormian bones. They occur most frequently in the course of the lambdoidal suture, but are occasionally seen at the fontanelles, especially the posterior. One, the pterion ossicle, sometimes exists between the sphenoidal angle of the parietal bone and the great wing of the sphenoid bone. They have a tendency to be more or less symmetrical on the two sides of the skull, and vary in size. Their number is generally limited to two or three; but more than a hundred have been found in the skull of an adult hydrocephalic subject. Note: Ole Worm, Professor of Anatomy at Copenhagen, 1624�1639, was erroneously supposed to have given the first detailed description of these bones.

Foramina of skull base

The following is a list of holes, or foramina, in the base of the skull and what goes through each of them. Arranged from anterior to posterior:

foramen caecum - emissary vein to superior sagittal sinus\n*foramina of cribriform plate - olfactory nerve bundles\n*posterior ethmoidal foramen - posterior ethmoidal artery, vein and nerve\n*optic canal - optic nerve (II), ophthalmic artery\n*superior orbital fissure\n**oculomotor nerve (III)\n**trochlear nerve (IV)\n**lacrimal, frontal and nasociliary branches of ophthalmic nerve (V₁)\n**abducens nerve (VI)\n**superior ophthalmic vein\n*foramen rotundum - maxillary nerve (V₂)\n*foramen ovale\n**mandibular nerve (V₃)\n**accessory meningeal artery\n**lesser petrosal nerve (occasionally)\n*foramen spinosum\n**middle meningeal artery and vein\n**meningeal branch of mandibular nerve\n*formamen lacerum\n**internal carotid artery\n**internal carotid nerve plexus\n*hiatus of canal of lesser petrosal nerve\n*hiatus of canal of greater petrosal nerve\n*internal acoustic meatus\n**facial nerve (VII)\n**vestibulocochlear nerve (VIII)\n**labyrinthine artery\n*jugular foramen\n**inferior petrosal sinus\n**glossopharyngeal nerve (IX)\n**vagus nerve (X)\n**accessory nerve (XI)\n**sigmoid sinus\n**posterior meningeal artery\n**internal jugular vein\n*hypoglossal canal - hypoglossal nerve (XII)\n*foramen magnum\n**medulla oblongata\n**meninges\n**vertebral arteries\n**meningeal branches of vertebral arteries\n**spinal roots of accessory nerves

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Skull

Humans

Bones of the human skull

Cranial bones

Facial bones

Ear ossicles

Wormian bones

Foramina of skull base

See also