The occipital bone () is a

cranial Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek language, Greek roots, describe something in its standard anatomical position. Thi ...

dermal bone A dermal bone or investing bone or membrane bone is a bony structure derived from intramembranous ossification forming components of the vertebrate skeleton, including much of the skull, jaws, gill covers, shoulder girdle, fin rays ( lepidotrich ...

and the main

bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...

of the occiput (back and lower part of the

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

). It is

trapezoid In geometry, a trapezoid () in North American English, or trapezium () in British English, is a quadrilateral that has at least one pair of parallel sides. The parallel sides are called the ''bases'' of the trapezoid. The other two sides are ...

al in shape and curved on itself like a shallow dish. The occipital bone lies over the

occipital lobe The occipital lobe is one of the four Lobes of the brain, major lobes of the cerebral cortex in the brain of mammals. The name derives from its position at the back of the head, from the Latin , 'behind', and , 'head'. The occipital lobe is the ...

s of the

cerebrum The cerebrum (: cerebra), telencephalon or endbrain is the largest part of the brain, containing the cerebral cortex (of the two cerebral hemispheres) as well as several subcortical structures, including the hippocampus, basal ganglia, and olfac ...

. At the

base of the skull The base of skull, also known as the cranial base or the cranial floor, is the most inferior area of the skull. It is composed of the endocranium and the lower parts of the calvaria. Structure Structures found at the base of the skull are for ...

in the occipital bone, there is a large oval opening called the

foramen magnum The foramen magnum () is a large, oval-shaped opening in the occipital bone of the skull. It is one of the several oval or circular openings (foramina) in the base of the skull. The spinal cord, an extension of the medulla oblongata, passes thro ...

, which allows the passage of the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal c ...

. Like the other cranial bones, it is classed as a

flat bone Flat bones are bones whose principal function is either extensive protection or the provision of broad surfaces for muscular attachment. These bones are expanded into broad, flat plates,'' Gray's Anatomy'' (1918). (See infobox) as in the cranium ...

. Due to its many attachments and features, the occipital bone is described in terms of separate parts. From its front to the back is the basilar part, also called the basioccipital, at the sides of the foramen magnum are the lateral parts, also called the exoccipitals, and the back is named as the squamous part. The basilar part is a thick, somewhat quadrilateral piece in front of the foramen magnum and directed towards the

pharynx The pharynx (: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea (the tubes going down to the stomach and the lungs respectively). It is found in vertebrates and invertebrates ...

. The squamous part is the curved, expanded plate behind the foramen magnum and is the largest part of the occipital bone. Due to its embryonic derivation from paraxial mesoderm (as opposed to neural crest, from which many other craniofacial bones are derived), it has been posited that "the occipital bone as a whole could be considered as a giant vertebra enlarged to support the brain."

Structure

The occipital bone, like the other seven

cranial bones In human anatomy, the neurocranium, also known as the braincase, brainpan, brain-pan, or brainbox, is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calv ...

, has outer and inner layers (also called ''plates'' or ''tables'') of cortical bone tissue between which is the cancellous bone tissue known in the cranial bones as

diploë Diploë ( or ) is the spongy cancellous bone separating the inner and outer layers of the cortical bone of the skull. It is a subclass of trabecular bone. In the cranial bones, the layers of compact cortical tissue are familiarly known as the ...

. The bone is especially thick at the ridges, protuberances,

condyles A condyle (;Entry "condyle"
in

, and anterior part of the basilar part; in the inferior cerebellar fossae it is thin, semitransparent, and without diploë.

Outer surface

Near the middle of the outer surface of the squamous part of the occipital (the largest part) there is a prominence – the

external occipital protuberance External may refer to: * Externality, in economics, the cost or benefit that affects a party who did not choose to incur that cost or benefit * Externals, a fictional group of X-Men antagonists See also * * Internal (disambiguation) {{disa ...

. The highest point of this is called the inion. From the inion, along the midline of the squamous part until the foramen magnum, runs a ridge – the

external occipital crest The external occipital crest is part of the external surface of the squamous part of the occipital bone. It is a ridge along the midline, beginning at the external occipital protuberance and descending to the foramen magnum, that gives attachment ...

(also called the medial nuchal line) and this gives attachment to the

nuchal ligament The nuchal ligament is a ligament at the back of the neck that is continuous with the supraspinous ligament. Structure The nuchal ligament extends from the external occipital protuberance on the skull and median nuchal line to the spinous p ...

. Running across the outside of the occipital bone are three curved lines and one line (the medial line) that runs down to the foramen magnum. These are known as the

nuchal line The nuchal lines are four curved lines on the external surface of the occipital bone: * The upper, often faintly marked, is named the highest nuchal line, but is sometimes referred to as the Mempin line or linea suprema, and it attaches to the ep ...

s which give attachment to various ligaments and muscles. They are named as the ''highest'', ''superior'' and ''inferior'' nuchal lines. The inferior nuchal line runs across the midpoint of the ''median'' nuchal line. The area above the highest nuchal line is termed the

occipital plane The squamous part of occipital bone is situated above and behind the foramen magnum, and is curved from above downward and from side to side. External surface The external surface is convex and presents midway between the summit of the bone and ...

and the area below this line is termed the

nuchal plane The squamous part of occipital bone is situated above and behind the foramen magnum, and is curved from above downward and from side to side. External surface The external surface is convex and presents midway between the summit of the bone and ...

Inner surface

The inner surface of the occipital bone forms the base of the

posterior cranial fossa The posterior cranial fossa is the part of the cranial cavity located between the foramen magnum, and tentorium cerebelli. It is formed by the sphenoid bones, temporal bones, and occipital bone. It lodges the cerebellum, and parts of the brai ...

. The

is a large hole situated in the middle, with the clivus, a smooth part of the occipital bone travelling upwards in front of it. The median internal occipital crest travels behind it to the

internal occipital protuberance Along the internal surface of the occipital bone, at the point of intersection of the four divisions of the cruciform eminence, is the internal occipital protuberance. Running transversely on either side is a groove for the transverse sinus. Addit ...

, and serves as a point of attachment to the

falx cerebri The falx cerebri (also known as the cerebral falx) is a large, crescent-shaped fold of dura mater that descends vertically into the longitudinal fissure to separate the cerebral hemispheres.Saladin K. "Anatomy & Physiology: The Unity of Form a ...

. To the sides of the

foramen In anatomy and osteology, a foramen (; : foramina, or foramens ; ) is an opening or enclosed gap within the dense connective tissue (bones and deep fasciae) of extant and extinct amniote animals, typically to allow passage of nerves, artery, ...

sitting at the junction between the lateral and base of the occipital bone are the

hypoglossal canal The hypoglossal canal is a foramen in the occipital bone of the skull. It is hidden medially and superiorly to each occipital condyle. It transmits the hypoglossal nerve. Structure The hypoglossal canal lies in the epiphyseal junction between ...

s. Further out, at each junction between the occipital and

petrous portion of the temporal bone The petrous part of the temporal bone is pyramid-shaped and is wedged in at the base of the skull between the sphenoid and occipital bones. Directed medially, forward, and a little upward, it presents a base, an apex, three surfaces, and three a ...

lies a

jugular foramen A jugular foramen is one of the two (left and right) large foramina (openings) in the base of the skull, located behind the carotid canal. It is formed by the temporal bone and the occipital bone. It allows many structures to pass, including the ...

. The inner surface of the occipital bone is marked by dividing lines as shallow ridges, that form four fossae or depressions. The lines are called the

cruciform A cruciform is a physical manifestation resembling a common cross or Christian cross. These include architectural shapes, biology, art, and design. Cruciform architectural plan Christian churches are commonly described as having a cruciform ...

(cross-shaped)

eminence Eminence may refer to: Places in the United States * Eminence, Arkansas, List of places in Arkansas: E, a place in Arkansas * Eminence, Indiana * Eminence, Kansas * Eminence, Kentucky * Eminence, Mississippi, in Covington County, Mississippi * Em ...

. At the midpoint where the lines intersect a raised part is formed called the

. From each side of this eminence runs a

groove Groove or Grooves may refer to: Music * Groove (music) * Groove (drumming) * The Groove (band), an Australian rock/pop band of the 1960s * The Groove (Sirius XM), a US radio station * Groove 101.7FM, a former Perth, Australia, radio station ...

for the

transverse sinuses The transverse sinuses (left and right lateral sinuses), within the human head, are two areas beneath the brain which allow blood to drain from the back of the head. They run laterally in a groove along the interior surface of the occipital bone ...

. There are two midline skull landmarks at the

. The

basion The foramen magnum () is a large, oval-shaped opening in the occipital bone of the skull. It is one of the several oval or circular openings (foramina) in the base of the skull. The spinal cord, an extension of the medulla oblongata, passes thro ...

is the most anterior point of the opening and the opisthion is the point on the opposite posterior part. The basion lines up with the dens.

Foramen magnum

The foramen magnum () is a large oval

longest front to back; it is wider behind than in front where it is encroached upon by the

occipital condyles The occipital condyles are undersurface protuberances of the occipital bone in vertebrates, which function in articulation with the superior facets of the Atlas (anatomy), atlas vertebra. The condyles are oval or reniform (kidney-shaped) in shape ...

. The clivus, a smooth bony section, travels upwards on the front surface of the foramen, and the median internal occipital crest travels behind it. Through the foramen passes the

medulla oblongata The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the brainstem. It is anterior and partially inferior to the cerebellum. It is a cone-shaped neuronal mass responsible for autonomic (involun ...

and its membranes, the

accessory nerve The accessory nerve, also known as the eleventh cranial nerve, cranial nerve XI, or simply CN XI, is a cranial nerve that supplies the sternocleidomastoid and trapezius muscles. It is classified as the eleventh of twelve pairs of cranial nerv ...

s, the

vertebral arteries The vertebral arteries are major arteries of the neck. Typically, the vertebral arteries originate from the subclavian arteries. Each vessel courses superiorly along each side of the neck, merging within the skull to form the single, midline ...

, the

anterior Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

and

posterior spinal arteries The posterior spinal artery (dorsal spinal arteries) arises from the vertebral artery in 25% of humans or the posterior inferior cerebellar artery in 75% of humans, adjacent to the medulla oblongata. It is usually double, and spans the length of th ...

, the

tectorial membrane The tectoria membrane (TM) is one of two acellular membranes in the cochlea of the inner ear, the other being the basilar membrane (BM). "Tectorial" in anatomy means forming a cover. The TM is located above the spiral limbus and the spiral org ...

and the

alar ligament In anatomy, the alar ligaments are ligaments which connect the dens (a bony protrusion on the second cervical vertebra) to tubercles on the medial side of the occipital condyle. They are short, tough, fibrous cords that attach on the skull and ...

Angles

The superior angle of the occipital bone articulates with the occipital angles of the

parietal bones The parietal bones ( ) are two bones in the skull which, when joined at a fibrous joint known as a cranial suture, form the sides and roof of the neurocranium. In humans, each bone is roughly quadrilateral in form, and has two surfaces, four bord ...

and, in the fetal skull, corresponds in position with the

posterior fontanelle The posterior fontanelle (lambdoid fontanelle, occipital fontanelle) is a gap between bones in the human skull (known as fontanelle), triangular in form and situated at the junction of the sagittal suture and lambdoidal suture. It generally closes ...

. The lateral angles are situated at the extremities of the groove for the transverse sinuses: each is received into the interval between the mastoid angle of the parietal bone, and the

mastoid portion of the temporal bone The mastoid part of the temporal bone is the posterior (back) part of the temporal bone, one of the bones of the skull. Its rough surface gives attachment to various muscles (via tendons) and it has Foramen, openings for blood vessels. From its bo ...

. The inferior angle is fused with the

body of the sphenoid bone The body of the sphenoid bone, more or less cubical in shape, is hollowed out in its interior to form two large cavities, the sphenoidal sinuses, which are separated from each other by a septum. Superior surface The superior surface of the body ...

Borders

The superior borders extend from the superior to the lateral angles: they are deeply serrated for articulation with the occipital borders of the parietals, and form by this union the

lambdoidal suture The lambdoid suture, or lambdoidal suture, is a dense, fibrous connective tissue joint on the posterior aspect of the skull that connects the parietal bones with the occipital bone. It is continuous with the occipitomastoid suture. Structure T ...

. The inferior borders extend from the lateral angles to the inferior angle; the upper half of each articulates with the mastoid portion of the corresponding temporal, the lower half with the petrous part of the same bone. These two portions of the inferior border are separated from one another by the

jugular process The jugular process is a quadrilateral or triangular bony plate projecting lateralward from the posterior half of the occipital condyle; it is a part of the lateral part of the occipital bone. The jugular process is excavated in front by the jugu ...

, the notch on the anterior surface of which forms the posterior part of the

Sutures

File:Lambdoid suture.png, Lambdoid suture File:Occipitomastoid suture.png, Occipitomastoid suture The

lambdoid suture The lambdoid suture, or lambdoidal suture, is a dense, fibrous connective tissue joint on the posterior aspect of the skull that connects the parietal bones with the occipital bone. It is continuous with the occipitomastoid suture. Structure T ...

joins the occipital bone to the

parietal bone The parietal bones ( ) are two bones in the skull which, when joined at a fibrous joint known as a cranial suture, form the sides and roof of the neurocranium. In humans, each bone is roughly quadrilateral in form, and has two surfaces, four bord ...

s. The

occipitomastoid suture The occipitomastoid suture, or occipitotemporal suture, is the cranial suture between the occipital bone and the mastoid portion of the temporal bone. It is continuous with the lambdoidal suture. See also * Jugular foramen Additional im ...

joins the occipital bone and

mastoid portion The mastoid part of the temporal bone is the posterior (back) part of the temporal bone, one of the bones of the skull. Its rough surface gives attachment to various muscles (via tendons) and it has openings for blood vessels. From its borders, t ...

of the

temporal bone The temporal bone is a paired bone situated at the sides and base of the skull, lateral to the temporal lobe of the cerebral cortex. The temporal bones are overlaid by the sides of the head known as the temples where four of the cranial bone ...

. The sphenobasilar suture joins the basilar part of the occipital bone and the back of the

sphenoid bone The sphenoid bone is an unpaired bone of the neurocranium. It is situated in the middle of the skull towards the front, in front of the basilar part of occipital bone, basilar part of the occipital bone. The sphenoid bone is one of the seven bon ...

body. The petrous-basilar suture joins the side edge of the basilar part of the occipital bone to the petrous-part of the

Development

The

ig. 3of the squamous part of the occipital bone is developed in

membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. Bi ...

, and may remain separate throughout life when it constitutes the

interparietal bone An interparietal bone (os interparietale or Inca bone or ''os inca var.'') is a dermal bone situated between the parietal and supraoccipital. It is homologous to the postparietal bones of other animals. In humans, it corresponds to the upper ...

; the rest of the bone is developed in cartilage. The number of nuclei for the occipital plane is usually given as four, two appearing near the middle line about the second month, and two some little distance from the middle line about the third month of fetal life. The

of the squamous part is ossified from two centers, which appear about the seventh week of fetal life and soon unite to form a single piece. Union of the upper and lower portions of the squamous part takes place in the third month of fetal life. An occasional centre ( Kerckring) appears in the posterior margin of the foramen magnum during the fifth month; this forms a separate ossicle (sometimes double) which unites with the rest of the squamous part before birth. Each of the lateral parts begins to

ossify Ossification (also called osteogenesis or bone mineralization) in bone remodeling is the process of laying down new bone material by cells named osteoblasts. It is synonymous with bone tissue formation. There are two processes resulting in the ...

from a single center during the eighth week of fetal life. The basilar portion is ossified from two centers, one in front of the other; these appear about the sixth week of fetal life and rapidly coalesce. The occipital plane is said to be ossified from two centers and the basilar portion from one. About the fourth year the squamous part and the two lateral parts unite, and by about the sixth year the bone consists of a single piece. Between the 18th and 25th years the occipital and

become united, forming a single bone.

Clinical significance

Trauma to the occiput can cause a fracture of the base of the skull, called a

basilar skull fracture A basilar skull fracture is a bone fracture, break of a bone in the base of skull, base of the skull. Symptoms may include Battle sign, bruising behind the ears, periorbital ecchymosis, bruising around the eyes, or hemotympanum, blood behind the ...

. The ''basion-dens line'' as seen on a

radiograph Radiography is an imaging technique using X-rays, gamma rays, or similar ionizing radiation and non-ionizing radiation to view the internal form of an object. Applications of radiography include medical ("diagnostic" radiography and "therapeu ...

is the distance between the basion and the top of the dens, used in the diagnosis of dissociation injuries.

Genetic disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene (monogenic) or multiple genes (polygenic) or by a chromosome abnormality. Although polygenic disorders ...

s can cause a prominent occiput as found in

Edwards syndrome Edwards may refer to: People * Edwards (surname), an English surname * Edwards family, a prominent family from Chile * Edwards Barham (1937–2014), American politician * Edwards Davis (1873–1936), American actor, producer, and playwright * Edwa ...

, and

Beckwith–Wiedemann syndrome Beckwith–Wiedemann syndrome (; abbreviated BWS) is an overgrowth disorder usually present at birth, characterized by an increased risk of childhood cancer and certain congenital features. A minority (97th centile) * Macroglossia * Hemihypertroph ...

. The identification of the location of the

fetal A fetus or foetus (; : fetuses, foetuses, rarely feti or foeti) is the unborn offspring of a viviparous animal that develops from an embryo. Following the embryonic stage, the fetal stage of development takes place. Prenatal development is a ...

occiput is important in

delivery Delivery may refer to: Biology and medicine *Childbirth *Drug delivery *Gene delivery Business and law *Delivery (commerce), of goods, e.g.: **Pizza delivery ** Milk delivery ** Food delivery ** Online grocer *Deed ("delivery" in contract law), a ...

Etymology

Occipital stems from Latin

occiput The occipital bone () is a cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone lies over the occipital lobes of the ...

"back of the skull", from ob "against, behind" + caput "head". Distinguished from sinciput (anterior part of the skull)."occipital" A Dictionary of Zoology. Ed. Michael Allaby.

Oxford University Press Oxford University Press (OUP) is the publishing house of the University of Oxford. It is the largest university press in the world. Its first book was printed in Oxford in 1478, with the Press officially granted the legal right to print books ...

2009

Other animals

In many animals these parts stay separate throughout life; for example, in the dog as four parts: squamous part (supraoccipital); lateral parts–left and right parts (exoccipital); basilar part (basioccipital). The occipital bone is part of the

endocranium The endocranium in comparative anatomy is a part of the skull base in vertebrates and it represents the basal, inner part of the cranium. The term is also applied to the outer layer of the dura mater in human anatomy. Structure Structurally, t ...

, the most basal portion of the skull. In

Chondrichthyes Chondrichthyes (; ) is a class of jawed fish that contains the cartilaginous fish or chondrichthyans, which all have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fish'', which have skeleto ...

and

Agnatha Agnatha (; ) or jawless fish is a paraphyletic infraphylum of animals in the subphylum Vertebrata of the phylum Chordata, characterized by the lack of jaws. The group consists of both extant taxon, living (Cyclostomi, cyclostomes such as hagfish ...

, the occipital does not form as a separate element, but remains part of the

chondrocranium The chondrocranium (or ''cartilaginous neurocranium'') is the primitive cartilaginous skeletal structure of the fetal skull that grows to envelop the rapidly growing embryonic brain.Salentijn, L. ''Biology of Mineralized Tissues: Prenatal Skul ...

throughout life. In most

higher vertebrates Amniotes are tetrapod vertebrate animals belonging to the clade Amniota, a large group that comprises the vast majority of living terrestrial and semiaquatic vertebrates. Amniotes evolved from amphibious stem tetrapod ancestors during the Ca ...

, the foramen magnum is surrounded by a ring of four bones. The basioccipital lies in front of the opening, the two exoccipital condyles lie to either side, and the larger supraoccipital lies to the posterior, and forms at least part of the rear of the cranium. In many

bony fish Osteichthyes ( ; ), also known as osteichthyans or commonly referred to as the bony fish, is a Biodiversity, diverse clade of vertebrate animals that have endoskeletons primarily composed of bone tissue. They can be contrasted with the Chondricht ...

and

amphibian Amphibians are ectothermic, anamniote, anamniotic, tetrapod, four-limbed vertebrate animals that constitute the class (biology), class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all Tetrapod, tetrapods, but excl ...

s, the supraoccipital is never ossified, and remains as

cartilage Cartilage is a resilient and smooth type of connective tissue. Semi-transparent and non-porous, it is usually covered by a tough and fibrous membrane called perichondrium. In tetrapods, it covers and protects the ends of long bones at the joints ...

throughout life. In primitive forms the basioccipital and exoccipitals somewhat resemble the centrum and neural arches of a

vertebra Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spina ...

, and form in a similar manner in the embryo. Together, these latter bones usually form a single concave circular

condyle A condyle (;Entry "condyle"
in

for the articulation of the first

. In

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

s, however, the condyle has divided in two, a pattern otherwise seen only in a few amphibians. Most mammals also have a single fused occipital bone, formed from the four separate elements around the foramen magnum, along with the paired

postparietal Postparietals are cranial bones present in fish and many Tetrapod, tetrapods. Although initially a pair of bones, many lineages possess postparietals which were fused into a single bone. The postparietals were Dermal bone, dermal bones situated alo ...

bones that form the rear of the cranial roof in other vertebrates.

Additional images

File:Occipital bone animation.gif, Position of occipital bone (shown in green). Animation. File:Occipital bone animation2.gif, Outer surface File:Occipital bone animation3.gif, Inner surface.

Frontal bone In the human skull, the frontal bone or sincipital bone is an unpaired bone which consists of two portions.'' Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bo ...

and

s are removed. File:Occipital bone.jpg, Occipital bone File:Occipital bone 2.jpg, Occipital bone File:Gray308.png, Median sagittal section through the occipital bone and first three cervical vertebræ File:Basilar part.jpg, Basilar part File:Slide4llll.JPG, Occipital bone