Occipital bone
The occipital bone (also known as C0) is a trapezoid skull bone that contributes to the posteroinferior part of the cranial vault. It is pierced by the foramen magnum, permitting communication from the cranial cavity to the vertebral canal.
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Terminology
Occiput is a noun referring to the back of the head, it is not a synonym for the occipital bone. The occipital bone is also known as "C0" because it joins the skull to the first cervical vertebra or C1, forming the atlanto-occipital joint.
Gross anatomy
The occipital bone is composed of four parts:
- squamous part: external/internal surfaces
- basilar part (basiocciput): lower/upper surfaces
- lateral (jugular) parts (two): under/upper surfaces
The squamous part is the curved, expanded plate located behind the foramen magnum.
The external surface of the squamous part features:
- external occipital protuberance, the tip is known as the inion
- highest nuchal line
- superior nuchal line: occipitalis, trapezius, sternocleidomastoid, splenius capitis
- inferior nuchal line: rectus capitis posterior major and minor
- median nuchal line: attachment of ligamentum nuchae
- attachment of posterior atlanto-occipital membrane
The internal surface of the squamous part features:
- cruciate eminence divide region into four fossa; the upper two contain the occipital lobes while the lower two contain the cerebellar hemispheres
- internal occipital tuberosity at intersection
- sagittal sulcus for superior sagittal sinus, falx cerebri attaches to margins
- internal occipital crest gives attachment to falx cerebelli
- transverse grooves hold transverse sinuses
The basilar part is the quadrilateral piece in front of the foramen magnum.
The lower surface of the basilar part features:
- pharyngeal tubercle: attachment to fibrous raphe of pharynx
- either side of middle line: longus capitis, and rectus capitis anterior
- anterior atlanto-occipital membrane
The upper surface of the basilar part features:
- the clivus has a broad, shallow groove, for medulla oblongata
- lateral grooves for the inferior petrosal sinus
The under surface of the lateral part features:
- occipital condyles: articulate with the atlas (C1), permitting flexion and extension (nodding) with minimal lateral flexion. No rotation occurs at the atlanto-occipital joint.
- the condyles are egg shaped and sloped inferomedially from anterior to posterior which helps limits mobility 2
- a third condyle may be a variant
- hypoglossal canal: at base of occipital condyles
- condylar fossa: behind condyle, receives posterior margin of superior facet of atlas, can be perforated by condyloid canal which contains an emissary vein from the transverse sinus
- jugular process, excavated in front by jugular notch, forming posterior part of jugular foramen
The upper surface of the lateral part features
- jugular tubercle: overlies hypoglossal canal, sometimes crossed by oblique groove for CN 9, 10, 11
Articulations
The occipital bone articulates with 6 bones:
- unpaired
- paired bones
Development
The apical portion of the squamous part (above highest nuchal line): ossifies in membrane. Otherwise, the four parts ossify in cartilage.
Four parts are present at birth. Fusion occurs:
- 2nd year: squamous and jugulars
- 6th year: jugulars with basilar
- 25th year: basilar with basisphenoid
Related Radiopaedia articles
Anatomy: Head and neck
- skeleton of the head and neck
-
cranial vault
- scalp (mnemonic)
- fontanelle
-
sutures
- calvarial
- facial
- frontozygomatic suture
- frontomaxillary suture
- frontolacrimal suture
- frontonasal suture
- temporozygomatic suture
- zygomaticomaxillary suture
- parietotemporal suture (parietomastoid suture)
- occipitotemporal suture (occipitomastoid suture)
- sphenofrontal suture
- sphenozygomatic suture
- spheno-occipital suture (not a true suture)
- lacrimomaxillary suture
- nasomaxillary suture
- internasal suture
- basal/internal
- skull landmarks
- frontal bone
- temporal bone
- parietal bone
- occipital bone
- skull base (foramina)
-
facial bones
- midline single bones
- paired bilateral bones
- cervical spine
- hyoid bone
- laryngeal cartilages
-
cranial vault
- muscles of the head and neck
- muscles of the tongue (mnemonic)
- muscles of mastication
-
muscles of facial expression
- occipitalis muscle
- circumorbital and palpebral muscles
- nasal muscles
- buccolabial muscles
- elevators, retractors and evertors of the upper lip
- levator labii superioris alaeque nasalis muscle
- levator labii superioris muscle
- zygomaticus major muscle
- zygomaticus minor muscle
- malaris muscle
- levator anguli oris muscle
- risorius muscle
- depressors, retractors and evertors of the lower lip
- depressor labii inferioris muscle
- depressor anguli oris muscle
- mentalis muscle
- compound sphincter
- orbicularis oris muscle
- incisivus superior muscle
- incisivus inferior muscle
- muscle of mastication:
- elevators, retractors and evertors of the upper lip
- muscles of the middle ear
- orbital muscles
- muscles of the soft palate
- pharyngeal muscles
- suprahyoid muscles
- infrahyoid muscles
- intrinsic muscles of the larynx
- muscles of the neck
- accessory muscles of the neck
- deep cervical fascia
-
deep spaces of the neck
- anterior cervical space
- buccal space
- carotid space
- danger space
- deep cervical fascia
- infratemporal fossa
- masticator space
- parapharyngeal space
- stylomandibular tunnel
- parotid space
- pharyngeal (superficial) mucosal space
- perivertebral space
- posterior cervical space
- pterygopalatine fossa
- retropharyngeal space
- suprasternal space (of Burns)
- visceral space
- surgical triangles of the neck
- orbit
- ear
- paranasal sinuses
- nose
- oral cavity
- pharynx
- larynx
- viscera of the neck
- blood supply of the head and neck
-
arterial supply
-
common carotid artery
- carotid body
- carotid bifurcation
- subclavian artery
- variants
-
common carotid artery
- venous drainage
-
arterial supply
- innervation of the head and neck
-
cranial nerves
- olfactory nerve (CN I)
- optic nerve (CN II)
- oculomotor nerve (CN III)
- trochlear nerve (CN IV)
-
trigeminal nerve (CN V) (mnemonic)
- trigeminal ganglion
- ophthalmic division
- maxillary division
- mandibular division
- abducens nerve (CN VI)
- facial nerve (CN VII)
-
vestibulocochlear nerve (CN VIII)
- vestibular ganglion (Scarpa's ganglion)
- glossopharyngeal nerve (CN IX)
-
vagus nerve (CN X)
- superior laryngeal nerve
- recurrent laryngeal nerve (inferior laryngeal nerve)
- (spinal) accessory nerve (CN XI)
- hypoglossal nerve (CN XII)
- parasympathetic ganglia of the head and neck
- greater occipital nerve
- third occipital nerve
-
cervical plexus
- muscular branches
- longus capitis
- longus colli
- scalenes
- geniohyoid
- thyrohyoid
-
ansa cervicalis
- omohyoid (superior and inferior bellies separately)
- sternothyroid
- sternohyoid
- phrenic nerve
- contribution to the accessory nerve (CN XI)
- cutaneous branches
- muscular branches
- brachial plexus
- pharyngeal plexus
-
cranial nerves
- lymphatic drainage of the head and neck
- embryological development of the head and neck