Lateral parts of occipital bone
Encyclopedia
The lateral parts of the occipital bone
are situated at the sides of the foramen magnum; on their under surfaces are the condyles for articulation with the superior facets of the atlas.
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 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, 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
.
Behind either condyle is a depression, the condyloid fossa
, which receives the posterior margin of the superior facet of the atlas
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.
Extending lateralward from the posterior half of the condyle is a quadrilateral plate of bone, the jugular process
, excavated in front by the jugular notch, which, in the articulated skull, forms the posterior part of the jugular foramen
.
The jugular notch may be divided into two by a bony spicule
, 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
.
Laterally the jugular process
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
.
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, vagus, and accessory nerve
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.
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
.
Occipital bone
The occipital bone, a saucer-shaped membrane bone situated at the back and lower part of the cranium, is trapezoidal in shape and curved on itself...
are situated at the sides of the foramen magnum; on their under surfaces are the condyles for articulation with the superior facets of the atlas.
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 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
Alar ligament
The alar ligaments connect the sides of the dens to tubercles on the medial side of the occipital condyle....
.
At the base of either condyle the bone is tunnelled by a short canal, the hypoglossal canal
Hypoglossal canal
The hypoglossal canal is a bony canal in the occipital bone of the skull.-Anatomy:It transmits the hypoglossal nerve from its point of entry near the medulla oblongata to its exit from the base of the skull near the jugular foramen...
(anterior condyloid foramen).
This begins on the cranial surface of the bone immediately above the foramen magnum, 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
Ascending pharyngeal artery
The ascending pharyngeal artery, the smallest branch of the external carotid, is a long, slender vessel, deeply seated in the neck, beneath the other branches of the external carotid and under the Stylopharyngeus...
.
Behind either condyle is a depression, the condyloid fossa
Condyloid fossa
Behind either condyle of the lateral parts of occipital bone is a depression, the condyloid fossa , which receives the posterior margin of the superior facet of the atlas when the head is bent backward; the floor of this fossa is sometimes perforated by the condyloid canal, through which an...
, which receives the posterior margin of the superior facet of the atlas
Atlas (anatomy)
In anatomy, the atlas is the most superior cervical vertebra of the spine.It is named for the Atlas of Greek mythology, because it supports the globe of the head....
when the head is bent backward; the floor of this fossa is sometimes perforated by the condyloid canal
Condyloid canal
The condylar canal is a canal in the condyloid fossa of the lateral parts of occipital bone behind the occipital condyle. Resection of the rectus capitus posterior major and minor muscles reveals the bony recess leading to the condylar canal, which is situated posterior and lateral to the...
, through which an emissary vein passes from the transverse sinus.
Extending lateralward from the posterior half of the condyle is a quadrilateral plate of bone, the jugular process
Jugular process
In the lateral part of the occipital bone, extending lateralward from the posterior half of the condyle is a quadrilateral plate of bone, the jugular process, excavated in front by the jugular notch, which, in the articulated skull, forms the posterior part of the jugular foramen.It serves as the...
, excavated in front by the jugular notch, which, in the articulated skull, forms the posterior part of the jugular foramen
Jugular foramen
The jugular foramen is a large aperture in the base of the skull. It is located behind the carotid canal and is formed in front by the petrous portion of the temporal, and behind by the occipital; it is generally larger on the right than on the left side....
.
The jugular notch may be divided into two by a bony spicule
Spicule
Spicules are tiny spike-like structures of diverse origin and function found in many organisms, such as the copulatory spicules of certain nematodes or the grains on the skin of some frogs.In sponges, spicules perform a structural function....
, 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
Atlas (anatomy)
In anatomy, the atlas is the most superior cervical vertebra of the spine.It is named for the Atlas of Greek mythology, because it supports the globe of the head....
.
Laterally the jugular process
Jugular process
In the lateral part of the occipital bone, extending lateralward from the posterior half of the condyle is a quadrilateral plate of bone, the jugular process, excavated in front by the jugular notch, which, in the articulated skull, forms the posterior part of the jugular foramen.It serves as the...
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
Ossification is the process of laying down new bone material by cells called osteoblasts. It is synonymous with bone tissue formation...
.
The upper surface of the lateral part presents an oval eminence, the jugular tubercle
Jugular tubercle
The upper surface of the lateral parts of occipital bone presents an oval eminence, the jugular tubercle, which overlies the hypoglossal canal and is sometimes crossed by an oblique groove for the glossopharyngeal, vagus, and accessory nerves.-External links:...
, which overlies the hypoglossal canal
Hypoglossal canal
The hypoglossal canal is a bony canal in the occipital bone of the skull.-Anatomy:It transmits the hypoglossal nerve from its point of entry near the medulla oblongata to its exit from the base of the skull near the jugular foramen...
and is sometimes crossed by an oblique groove for the glossopharyngeal, vagus, and accessory nerve
Accessory nerve
In anatomy, the accessory nerve is a nerve that controls specific muscles of the shoulder and neck. As part of it was formerly believed to originate in the brain, it is considered a cranial nerve...
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.
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
Condyloid canal
The condylar canal is a canal in the condyloid fossa of the lateral parts of occipital bone behind the occipital condyle. Resection of the rectus capitus posterior major and minor muscles reveals the bony recess leading to the condylar canal, which is situated posterior and lateral to the...
.