The lateral parts of the
occipital bone
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 overlies the occipital lobes of the cer ...
(also called the exoccipitals) are situated at the sides of the
foramen magnum
The foramen magnum ( la, great hole) 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 oblon ...
; on their under surfaces are the
condyle
A condyle (;Entry "condyle"
in
atlas
An atlas is a collection of maps; it is typically a bundle of maps of Earth or of a region of Earth.
Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats. In addition to presenting geogra ...
.
Description
The condyles are oval or reniform (kidney-shaped) in shape, and their anterior extremities, directed forward and medialward, are closer together than their posterior, and encroach on the
basilar portion of the bone; the posterior extremities extend back to the level of the middle of the
foramen magnum
The foramen magnum ( la, great hole) 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 oblon ...
.
The articular surfaces of the condyles are convex from before backward and from side to side, and look downward and lateralward.
To their margins are attached the capsules of the
atlantoöccipital articulations, and on the medial side of each is a rough impression or tubercle for the
alar ligament.
At the base of either condyle the bone is tunnelled by a short canal, the
hypoglossal canal (anterior condyloid foramen).
This begins on the cranial surface of the bone immediately above the
foramen magnum
The foramen magnum ( la, great hole) 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 oblon ...
, and is directed lateralward and forward above the condyle.
It may be partially or completely divided into two by a spicule of bone; it gives exit to the
hypoglossal or twelfth
cerebral nerve, and entrance to a meningeal branch of the
ascending pharyngeal artery
The ascending pharyngeal artery is an artery in the neck that supplies the pharynx, developing from the proximal part of the embryonic second aortic arch.
It is the smallest branch of the external carotid and is a long, slender vessel, deeply se ...
.
Behind either condyle is a depression, the
condyloid fossa, which receives the posterior margin of the superior facet of the
atlas
An atlas is a collection of maps; it is typically a bundle of maps of Earth or of a region of Earth.
Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats. In addition to presenting geogra ...
when the head is bent backward; the floor of this fossa is sometimes perforated by the
condyloid canal, through which an emissary vein passes from the
transverse sinus
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. ...
.
Extending lateralward from the posterior half of the condyle is a quadrilateral plate of bone, 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 ...
, excavated in front by the
jugular notch
The suprasternal notch, also known as the fossa jugularis sternalis, jugular notch, or Plender gap, is a large, visible dip in between the neck in humans, between the clavicles, and above the manubrium of the sternum.
Structure
The suprasternal ...
, which, in the articulated skull, forms the posterior part of the
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 jugular notch may be divided into two by a bony
spicule
Spicules are any of various small needle-like anatomical structures occurring in organisms
Spicule may also refer to:
*Spicule (sponge), small skeletal elements of sea sponges
*Spicule (nematode), reproductive structures found in male nematodes ( ...
, the intrajugular process, which projects lateralward above the hypoglossal canal.
The under surface of the jugular process is rough, and gives attachment to the
Rectus capitis lateralis muscle and the
lateral atlanto-occipital ligament; from this surface an eminence, the paramastoid process, sometimes projects downward, and may be of sufficient length to reach, and articulate with, the transverse process of the
atlas
An atlas is a collection of maps; it is typically a bundle of maps of Earth or of a region of Earth.
Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats. In addition to presenting geogra ...
.
Laterally 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 ...
presents a rough quadrilateral or triangular area which is joined to the jugular surface of the temporal bone by a plate of cartilage; after the age of twenty-five this plate tends 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 th ...
.
The upper surface of the lateral part presents an oval eminence, the
jugular tubercle, which overlies the
hypoglossal canal and is sometimes crossed by an oblique groove for the
glossopharyngeal
The glossopharyngeal nerve (), also known as the ninth cranial nerve, cranial nerve IX, or simply CN IX, is a cranial nerve that exits the brainstem from the sides of the upper medulla, just anterior (closer to the nose) to the vagus nerve. B ...
,
vagus
The vagus nerve, also known as the tenth cranial nerve, cranial nerve X, or simply CN X, is a cranial nerve that interfaces with the parasympathetic control of the heart, lungs, and digestive tract. It comprises two nerves—the left and right v ...
, and
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.
On the upper surface of the jugular process is a deep groove which curves medialward and forward and is continuous with the
jugular notch
The suprasternal notch, also known as the fossa jugularis sternalis, jugular notch, or Plender gap, is a large, visible dip in between the neck in humans, between the clavicles, and above the manubrium of the sternum.
Structure
The suprasternal ...
.
This groove lodges the terminal part of the transverse sinus, and opening into it, close to its medial margin, is the orifice of the
condyloid canal.
Additional images
File:Lateral parts of occipital bone - animation06.gif, Human cranium seen from below. Lateral parts of occipital bone shown in red.
File:Lateral parts of occipital bone - animation01.gif, Occipital bone
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 overlies the occipital lobes of the cer ...
. Lateral parts shown in red.
File:Gray131 Lateral parts of occipital bone.png, Occipital bone
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 overlies the occipital lobes of the cer ...
at birth, outer surface. (Lateral parts shown in yellow.)
File:Gray130.png, Occipital bone, inner surface.
References
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Bones of the head and neck