Arachnoid granulations are small protrusions of the arachnoid mater into the outer membrane of the dura mater. They protrude into the dural venous sinuses of the brain, allow cerebrospinal fluid to exit the subarachnoid space and enter the blood stream; the largest granulations lie along the superior sagittal sinus, a large venous space running from front to back along the center of the head. They are, present along other dural sinuses as well. Diffusion across the arachnoid granulations into the superior sagittal sinus returns CSF to the venous circulation; the arachnoid granulations act as one-way valves. The pressure of the CSF is higher than that of the venous system, so CSF flows through the villi and granulations into the blood. If the pressure is reversed for some reason, fluid will not pass back into the subarachnoid space; the reason for this is not known. It has been suggested that the endothelial cells of the venous sinus create vacuoles of CSF, which move through the cell and out into the blood.
The importance of arachnoid granulations for the drainage of CSF is controversial. By some accounts, a large portion of CSF is drained through lymphatics associated with extracranial segments of the cranial nerves. A large proportion of CSF is believed to leave the cranial vault through the axons of CN I through their extension through the cribriform plate. On the inner surface of cranial bones, small pits called granular fovea are produced by arachnoid granulations, they are referred to by their old name: Pacchioni's granulations or pacchionian bodies, named after Italian anatomist Antonio Pacchioni
The squamosal suture, or squamous suture, arches backward from the pterion and connects the temporal squama with the lower border of the parietal bone: this suture is continuous behind with the short, nearly horizontal parietomastoid suture, which unites the mastoid process of the temporal with the region of the mastoid angle of the parietal bone. "Anatomy diagram: 34256.000-2". Roche Lexicon - illustrated navigator. Elsevier. Archived from the original on 2014-01-01
The lambdoid 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, its name comes from its uppercase lambda-like shape. At birth, the bones of the skull do not meet. If certain bones of the skull grow too fast craniosynostosis may occur; this can result in skull deformities. If the lambdoid suture closes too soon on one side, the skull will appear twisted and asymmetrical, a condition called "plagiocephaly". Plagiocephaly refers to not the condition; the condition is craniosynostosis. The lambdoidal suture articulates with parietal bones. "Sagittal suture." Stedman's Medical Dictionary, 27th ed.. Moore, Keith L. and T. V. N. Persaud; the Developing Human: Clinically Oriented Embryology, 7th ed.. Anatomy figure: 22:01-03 at Human Anatomy Online, SUNY Downstate Medical Center Anatomy figure: 22:03-02 at Human Anatomy Online, SUNY Downstate Medical Center "Anatomy diagram: 34256.000-2".
Roche Lexicon - illustrated navigator. Elsevier. Archived from the original on 2014-01-01
The bregma is the anatomical point on the skull at which the coronal suture is intersected perpendicularly by the sagittal suture. The bregma is located at the intersection of the coronal suture and the sagittal suture on the superior middle portion of the calvaria, it is the point where parietal bones meet. The bregma is known as the anterior fontanelle during infancy; the anterior fontanelle closes in the first 18-36months of life. In the congenital disorder cleidocranial dysostosis, the anterior fontanelle never closes to form the bregma; the bregma is used as a reference point for stereotactic surgery of the brain. Examination of an infant includes palpating the anterior fontanelle. A sunken fontanelle indicates dehydration, whereas a tense or bulging anterior fontanelle indicates raised intracranial pressure. Bregma comes from the Greek bregma; this article incorporates text in the public domain from page 135 of the 20th edition of Gray's Anatomy lesson1 at The Anatomy Lesson by Wesley Norman
The occipital artery arises from the external carotid artery opposite the facial artery. Its path is below the posterior belly of digastric to the occipital region; this artery supplies blood to the back of the scalp and sterno-mastoid muscles, deep muscles in the back and neck. At its origin, it is covered by the posterior belly of the digastricus and the stylohyoideus, the hypoglossal nerve winds around it from behind forward, it next ascends to the interval between the transverse process of the atlas and the mastoid process of the temporal bone, passes horizontally backward, grooving the surface of the latter bone, being covered by the sternocleidomastoideus, splenius capitis, longissimus capitis, digastricus, resting upon the rectus capitis lateralis, the obliquus superior, semispinalis capitis. It changes its course and runs vertically upward, pierces the fascia connecting the cranial attachment of the trapezius with the sternocleidomastoideus, ascends in a tortuous course in the superficial fascia of the scalp, where it divides into numerous branches, which reach as high as the vertex of the skull and anastomose with the posterior auricular and superficial temporal arteries.
Muscular branches: supply the digastric, stylohyoid and longus capitis muscles. Sternocleidomastoid branch: This branch divides into upper and lower branches in the carotid triangle; the upper branch accompanies the accessory nerve to the sternocleidomastoid, the lower branch arises near the origin of the occipital artery before entering the sternocleidomastoid muscle. This branch arises directly from the external carotid artery. Auricular branch: supplies the back of the ear. In many specimens, this branch gives rise to the mastoid branch, which supplies the dura mater and mastoid air cells. In other specimens, the mastoid artery is a branch of the occipital artery, rather than the auricular branch. Meningeal branch: supplies the dura mater in the posterior cranial fossa Descending branches: This is the largest branch, it descends on the posterior aspect of the neck, divides into a superficial and deep portion. The superficial portion supplies the trapezius muscle and anastomoses with the ascending branch of the transverse cervical.
The deep portion anastomoses with the vertebral artery and with the a. profunda cervicalis, a branch of the costocervical trunk. Thus, branches of the occipital artery participate in anastamosis between the external carotid and the subclavian artery, thereby providing collateral circulation, its terminal portion is accompanied by the greater occipital nerve. This article incorporates text in the public domain from page 556 of the 20th edition of Gray's Anatomy lesson4 at The Anatomy Lesson by Wesley Norman Diagram at stchas.edu Description at okstate.edu http://www.dartmouth.edu/~humananatomy/figures/chapter_47/47-2. HTM
The occipital bone is a cranial dermal bone and the main bone of the occiput. It is trapezoidal in shape and curved on itself like a shallow dish; the occipital bone overlies the occipital lobes of the cerebrum. At the base of skull in the occipital bone, there is a large oval opening called the foramen magnum, which allows the passage of the spinal cord. Like the other cranial bones, it is classed as a flat bone. 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 called the basioccipital, at the sides of the foramen magnum are the lateral parts called the exoccipitals, 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 squamous part is the curved, expanded plate behind the foramen magnum and is the largest part of the occipital bone; the occipital bone, like the other seven cranial bones, has outer and inner layers of cortical bone tissue between, the cancellous bone tissue known in the cranial bones as diploë.
The bone is thick at the ridges, protuberances and anterior part of the basilar part. Near the middle of the outer surface of the squamous part of the occipital there is a prominence – the external occipital protuberance; 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 and this gives attachment to the nuchal ligament. Running across the outside of the occipital bone are three curved lines and one line that runs down to the foramen magnum; these are known as the nuchal lines which give attachment to various muscles. They are named as the highest and inferior nuchal lines; the inferior nuchal line runs across the midpoint of the medial nuchal line. The area above the highest nuchal line is termed the occipital plane and the area below this line is termed the nuchal plane; the inner surface of the occipital bone forms the base of the posterior cranial fossa. The foramen magnum 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, serves as a point of attachment to the falx cerebri. To the sides of the foramen sitting at the junction between the lateral and base of the occipital bone are the hypoglossal canals. Further out, at each junction between the occipital and petrous portion of the temporal bone lies a jugular foramen; 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 eminence. At the midpoint where the lines intersect a raised part is formed called the internal occipital protuberance. From each side of this eminence runs a groove for the transverse sinuses. There are two midline skull landmarks at the foramen magnum; the basion 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; the foramen magnum is a large oval foramen longest front to back.
The clivus, a smooth bony section, travels upwards on the front surface of the foramen, the median internal occipital crest travels behind it. Through the foramen passes the medulla oblongata and its membranes, the accessory nerves, the vertebral arteries, the anterior and posterior spinal arteries, the tectorial membrane and alar ligaments; the superior angle of the occipital bone articulates with the occipital angles of the parietal bones and, in the fetal skull, corresponds in position with the posterior fontanelle. 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, the mastoid portion of the temporal bone; the inferior angle is fused with the body of the sphenoid bone. The superior borders extend from the superior to the lateral angles: they are serrated for articulation with the occipital borders of the parietals, form by this union the lambdoidal suture; the inferior borders extend from the lateral angles to the inferior angle.
These two portions of the inferior border are separated from one another by the jugular process, the notch on the anterior surface of which forms the posterior part of the jugular foramen. The lambdoid suture joins the occipital bone to the parietal bones; the occipitomastoid suture joins the occipital mastoid portion of the temporal bone. The sphenobasilar suture joins the basilar part of the occipital bone and the back of the sphenoid bone body; the petrous-basilar suture joins the side edge of the basilar part of the occipital bone to the petrous-part of the temporal bone. The occipital plane of the squamous part of the occipital bone is developed in membrane, may remain separate throughout life when it constitutes the interparietal bone; the number of nuclei for the occipital plane is given as four, two appearing near the middle line about the second month, two some little distance from the middle line about the third month of
Anatomical terms of bone
Many anatomical terms descriptive of bone are defined in anatomical terminology, are derived from Greek and Latin. A long bone is one, cylindrical in shape, being longer than it is wide. However, the term describes the shape of a bone, not its size, relative. Long bones are found in the legs, as well as in the fingers and toes. Long bones function as levers, they are responsible for the body's height. A short bone is one, cube-like in shape, being equal in length and thickness; the only short bones in the human skeleton are in the carpals of the wrists and the tarsals of the ankles. Short bones provide support as well as some limited motion; the term “flat bone” is something of a misnomer because, although a flat bone is thin, it is often curved. Examples include the cranial bones, the scapulae, the sternum, the ribs. Flat bones serve as points of attachment for muscles and protect internal organs. Flat bones do not have a medullary cavity. An irregular bone is one that does not have an classified shape and defies description.
These bones tend to have more complex shapes, like the vertebrae that support the spinal cord and protect it from compressive forces. Many facial bones the ones containing sinuses, are classified as irregular bones. A sesamoid bone is a round bone that, as the name suggests, is shaped like a sesame seed; these bones form in tendons. The sesamoid bones protect tendons by helping them overcome compressive forces. Sesamoid bones vary in number and placement from person to person but are found in tendons associated with the feet and knees; the only type of sesamoid bone, common to everybody is the kneecap, the largest of the sesamoid bones. A condyle is the round prominence at the end of a bone, most part of a joint – an articulation with another bone; the epicondyle refers to a projection near a condyle the medial epicondyle of the humerus. These terms derive from Greek. An eminence refers to a small projection or bump of bone, such as the medial eminence. A process refers to a large projection or prominent bump, as does a promontory such as the sacral promontory.
Both tubercle and tuberosity refer to a projection or bump with a roughened surface, with a "tubercle" smaller than a "tuberosity". These terms are derived from Tuber. A ramus refers to an extension of bone, such as the ramus of the mandible in the jaw or Superior pubic ramus. Ramus may be used to refer to nerves, such as the ramus communicans. A facet refers to a flattened articular surface. A line refers to a long, thin projection with a rough surface. Ridge and crest refer to a narrow line. Unlike many words used to describe anatomical terms, the word ridge is derived from Old English. A spine, as well as referring to the spinal cord, may be used to describe a long, thin projection or bump; these terms are used to describe bony protuberances in specific parts of the body. The Malleolus is the bony prominence on each side of the ankle; these are known as the lateral malleolus. Each leg is supported by two bones, the tibia on the inner side of the leg and the fibula on the outer side of the leg; the medial malleolus is the prominence on the inner side of the ankle, formed by the lower end of the tibia.
The lateral malleolus is the prominence on the outer side of the ankle, formed by the lower end of the fibula. The trochanters are parts of the femur, it may refer to the greater, lesser, or third trochanter The following terms are used to describe cavities that connect to other areas: A foramen is any opening referring to those in bone. Foramina inside the body of humans and other animals allow muscles, arteries, veins, or other structures to connect one part of the body with another. A canal is a long, tunnel-like foramen a passage for notable nerves or blood vessels; the following terms are used to describe cavities that do not connect to other areas: A fossa is a depression or hollow in a bone, such as the hypophyseal fossa, the depression in the sphenoid bone. A meatus is a short canal. A fovea is a small pit on the head of a bone. An example of a fovea is the fovea capitis of the head of the femur; the following terms are used to describe the walls of a cavity: A labyrinth refers to the bony labyrinth and membranous labyrinth, components of the inner ear, due to their fine and complex structure.
A sinus refers to a bony cavity within the skull. A joint, or articulation is the region where adjacent bones contact each other, for example the elbow, shoulder, or costovertebral joint. Terms that refer to joints include: articular process, referring to a projection that contacts an adjacent bone. Suture, referring to an articulation between cranial bones. Bones are described with the terms head, shaft and base The head of a bone refers to the proximal end of the bone; the shaft refers to the elongated sections of long bone, the neck the segment between the head and shaft. The end of the long bone opposite to the head is known as the base; the cortex of a bone is used to refer to its outer layers, medulla used to