Squama occipitalis
Encyclopedia
The squama of the occipital bone
, situated above and behind the foramen magnum, is curved from above downward and from side to side.
(or inion).
Extending lateralward from this on either side are two curved lines, one a little above the other. The upper, often faintly marked, is named the highest nuchal line, and to it the galea aponeurotica
is attached.
The lower is termed the superior nuchal line. That part of the squama which lies above the highest nuchal lines is named the planum occipitale and is covered by the Occipitalis muscle. That below, termed the planum nuchale, is rough and irregular for the attachment of several muscles.
From the external occipital protuberance, an often faintly marked ridge or crest, the median nuchal line, descends to the foramen magnum and affords attachment to the ligamentum nuchæ. Running from the middle of this line across either half of the nuchal plane is the inferior nuchal line.
Several muscles are attached to the outer surface of the squama
, thus the superior nuchal line gives origin to the Occipitalis and Trapezius, and insertion to the Sternocleidomastoideus and Splenius capitis. Into the surface between the superior and inferior nuchal lines the Semispinalis capitis
and the Obliquus capitis superior are inserted, while the inferior nuchal line and the area below it receive the insertions of the Recti capitis posteriores major and minor.
The posterior atlantoöccipital membrane
is attached around the postero-lateral part of the foramen magnum, just outside the margin of the foramen.
The upper two fossæ are triangular and lodge the occipital lobes of the cerebrum; the lower two are quadrilateral and accommodate the hemispheres of the cerebellum
.
At the point of intersection of the four divisions of the cruciate eminence is the internal occipital protuberance.
From this protuberance the upper division of the cruciate eminence runs to the superior angle of the bone, and on one side of it (generally the right) is a deep groove, the sagittal sulcus, which lodges the hinder part of the superior sagittal sinus
. To the margins of this sulcus the falx cerebri
is attached.
The lower division of the cruciate eminence is prominent and is named the internal occipital crest; it bifurcates near the foramen magnum and gives attachment to the falx cerebelli
. In the attached margin of this falx is the occipital sinus, which is sometimes duplicated.
In the upper part of the internal occipital crest, a small depression is sometimes distinguishable; it is termed the vermian fossa since it is occupied by part of the vermis of the cerebellum. Transverse grooves
, one on either side, extend from the internal occipital protuberance to the lateral angles of the bone; those grooves accommodate the transverse sinuses, and their prominent margins give attachment to the tentorium cerebelli.
The groove on the right side is usually larger than that on the left and is continuous with that for the superior sagittal sinus
.
Exceptions to this condition are, however, not infrequent: the left may be larger than the right or the two may be almost equal in size.
The angle of union of the superior sagittal and transverse sinuses is named the confluence of the sinuses (torcular Herophili), and its position is indicated by a depression situated on one or other side of the protuberance.
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...
, situated above and behind the foramen magnum, 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 the foramen magnum a prominence, the external occipital protuberanceExternal occipital protuberance
Near the middle of the occipital squama is the external occipital protuberance, and extending lateralward from it on either side is the superior nuchal line, and above this the faintly marked highest nuchal line.It is less pronounced in females....
(or inion).
Extending lateralward from this on either side are two curved lines, one a little above the other. The upper, often faintly marked, is named the highest nuchal line, and to it the galea aponeurotica
Galea aponeurotica
The galea aponeurotica is a tough layer of dense fibrous tissue which covers the upper part of the cranium; behind, it is attached, in the interval between its union with the Occipitales, to the external occipital protuberance and highest nuchal lines of the occipital bone; in front, it forms a...
is attached.
The lower is termed the superior nuchal line. That part of the squama which lies above the highest nuchal lines is named the planum occipitale and is covered by the Occipitalis muscle. That below, termed the planum nuchale, is rough and irregular for the attachment of several muscles.
From the external occipital protuberance, an often faintly marked ridge or crest, the median nuchal line, descends to the foramen magnum and affords attachment to the ligamentum nuchæ. Running from the middle of this line across either half of the nuchal plane is the inferior nuchal line.
Several muscles are attached to the outer surface of the squama
Squama
Squama refers to a structure shaped like the scale of a fish. More specifically, it can refer to:* Squama frontalis* Squama occipitalis* Squama temporalis, the squamous portion of the temporal bone* Squamous cell...
, thus the superior nuchal line gives origin to the Occipitalis and Trapezius, and insertion to the Sternocleidomastoideus and Splenius capitis. Into the surface between the superior and inferior nuchal lines the Semispinalis capitis
Semispinalis capitis
The Semispinalis capitis is situated at the upper and back part of the neck, deep to the Splenius, and medial to the Longissimus cervicis and capitis....
and the Obliquus capitis superior are inserted, while the inferior nuchal line and the area below it receive the insertions of the Recti capitis posteriores major and minor.
The posterior atlantoöccipital membrane
Posterior atlantoöccipital membrane
The posterior atlantoöccipital membrane , broad but thin, is connected above, to the posterior margin of the foramen magnum; below, to the upper border of the posterior arch of the atlas....
is attached around the postero-lateral part of the foramen magnum, just outside the margin of the foramen.
Internal surface
The internal surface is deeply concave and divided into four fossæ by a cruciate eminence.The upper two fossæ are triangular and lodge the occipital lobes of the cerebrum; the lower two are quadrilateral and accommodate the hemispheres of the cerebellum
Cerebellum
The cerebellum is a region of the brain that plays an important role in motor control. It may also be involved in some cognitive functions such as attention and language, and in regulating fear and pleasure responses, but its movement-related functions are the most solidly established...
.
At the point of intersection of the four divisions of the cruciate eminence is the internal occipital protuberance.
From this protuberance the upper division of the cruciate eminence runs to the superior angle of the bone, and on one side of it (generally the right) is a deep groove, the sagittal sulcus, which lodges the hinder part of the superior sagittal sinus
Superior sagittal sinus
The superior sagittal sinus , within the human head, is an unpaired area along the attached margin of falx cerebri. It allows blood to drain from the lateral aspects of anterior cerebral hemispheres to the confluence of sinuses...
. To the margins of this sulcus the falx cerebri
Falx cerebri
The falx cerebri, also known as the cerebral falx, so named from its sickle-like form, is a strong, arched fold of dura mater which descends vertically in the longitudinal fissure between the cerebral hemispheres....
is attached.
The lower division of the cruciate eminence is prominent and is named the internal occipital crest; it bifurcates near the foramen magnum and gives attachment to the falx cerebelli
Falx cerebelli
The falx cerebelli is a small triangular process of dura mater, received into the posterior cerebellar notch.Its base is attached, above, to the under and back part of the tentorium cerebelli; its posterior margin, to the lower division of the vertical crest on the inner surface of the occipital...
. In the attached margin of this falx is the occipital sinus, which is sometimes duplicated.
In the upper part of the internal occipital crest, a small depression is sometimes distinguishable; it is termed the vermian fossa since it is occupied by part of the vermis of the cerebellum. Transverse grooves
Groove for transverse sinus
Along the internal surface of the occipital bone, running laterally between superior and inferior fossae of the cruciate eminence is the groove for transverse sinus. The transverse sinuses travel along this groove.-External links:*...
, one on either side, extend from the internal occipital protuberance to the lateral angles of the bone; those grooves accommodate the transverse sinuses, and their prominent margins give attachment to the tentorium cerebelli.
The groove on the right side is usually larger than that on the left and is continuous with that for the superior sagittal sinus
Sagittal sinus
Sagittal sinus can refer to:* Superior sagittal sinus* Inferior sagittal sinus...
.
Exceptions to this condition are, however, not infrequent: the left may be larger than the right or the two may be almost equal in size.
The angle of union of the superior sagittal and transverse sinuses is named the confluence of the sinuses (torcular Herophili), and its position is indicated by a depression situated on one or other side of the protuberance.