External occipital protuberance
Near the middle of the squamous part of occipital bone is the external occipital protuberance, the highest point of, referred to as the inion. The inion is the most prominent projection of the protuberance, located at the posterioinferior part of the human skull; the nuchal ligament and trapezius muscle attach to it. The inion is used as a landmark in the 10-20 system in electroencephalography recording. Extending laterally from it on either side is the superior nuchal line, above it is the faintly marked highest nuchal line. A study of 16th-century Anatolian remains showed that the external occipital protuberance statistically tends to be less pronounced in female remains. Internal occipital protuberance This article incorporates text in the public domain from page 185 of the 20th edition of Gray's Anatomy "Anatomy diagram: 34257.000-1". Roche Lexicon - illustrated navigator. Elsevier. Archived from the original on 2014-01-01. Http://www.upstate.edu/cdb/grossanat/hnsklatob1.shtml
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
The diploic veins are large, thin-walled valveless veins that channel in the diploë between the inner and outer layers of the cortical bone in the skull. They are lined by a single layer of endothelium supported by elastic tissue, they develop by the age of two years. The diploic veins drain this area into the dural venous sinuses; the four major trunks of the diploic veins found on each side of the head are frontal, anterior temporal, posterior temporal, occipital diploic veins. The frontal, which opens into the supraorbital vein and the superior sagittal sinus; the anterior temporal, confined chiefly to the frontal bone, opens into the sphenoparietal sinus and into one of the deep temporal veins, through an aperture in the great wing of the sphenoid. The posterior temporal, situated in the parietal bone, ends in the transverse sinus, through an aperture at the mastoid angle of the parietal bone or through the mastoid foramen; the occipital, the largest of the four, confined to the occipital bone, opens either externally into the occipital vein, or internally into the transverse sinus or into the confluence of the sinuses
The falx cerebri is known as the cerebral falx, named from its sickle-like form. It is a large, crescent-shaped fold of meningeal layer of dura mater that descends vertically in the longitudinal fissure between the cerebral hemispheres of the human brain; the falx cerebri attaches anteriorly at the crista galli in proximity to the cribriform plate and to the frontal and ethmoid sinuses. Posteriorly, it is connected with the upper surface of the cerebellar tentorium, its superior margin is attached at midline to the internal surface of skull, as far back as the internal occipital protuberance. The superior sagittal sinus is contained in the superior margin of the falx cerebri and overlies the longitudinal fissure of the brain; the inferior sagittal sinus is contained in the inferior margin of the falx cerebri and arches over the corpus callosum, deep in the longitudinal fissure. Calcification of the falx cerebri is more prevalent in older patients without a determinable cause, without pathogenic symptoms.
Falcine meningioma is a meningioma arising from the falx cerebri and concealed by the overlying cortex. Falcine meningioma tends to grow predominately into one cerebral hemisphere but is bilateral, in some patients the tumor grows into the inferior edge of the sagittal sinus. However, although much information is available regarding meningiomas, little is known about falcine meningiomas. Falx —other parts of the anatomy with names including "falx" This article incorporates text in the public domain from page 873 of the 20th edition of Gray's Anatomy Anatomy photo:28:st-1602 at the SUNY Downstate Medical Center MedEd at Loyola grossanatomy/dissector/labs/h_n/cranium/cn1_1a.htm
The facial skeleton comprises the facial bones that may attach to build a portion of the skull. The remainder of the skull is the braincase. In human anatomy and development, the facial skeleton is sometimes called the membranous viscerocranium, which comprises the mandible and dermatocranial elements that are not part of the braincase. In the human skull, the facial skeleton consists of fourteen bones in the face: Inferior nasal concha Lacrimal bones Mandible Maxilla Nasal bones Palatine bones Vomer Zygomatic bones Elements of the cartilaginous viscerocranium, such as the hyoid bone, are sometimes considered part of the facial skeleton; the ethmoid bone and the sphenoid bone are sometimes included, but otherwise considered part of the neurocranium. Because the maxillary bones are fused, they are collectively listed as only one bone; the mandible is considered separately from the cranium. The facial skeleton is composed of dermal bone and derived from the neural crest cells or from the sclerotome, which derives from the somite block of the mesoderm.
As with the neurocranium, in Chondricthyes and other cartilaginous vertebrates, they are not replaced via endochondral ossification. Variation in craniofacial form between humans is due to differing patterns of biological inheritance. Cross-analysis of osteological variables and genome-wide SNPs has identified specific genes that control this craniofacial development. Of these genes, DCHS2, RUNX2, GLI3, PAX1 and PAX3 were found to determine nasal morphology, whereas EDAR impacts chin protrusion. Axial skeleton Appendicular skeleton ent/9 at eMedicine - "Facial Bone Anatomy"
The anterior fontanelle is the largest fontanelle, is placed at the junction of the sagittal suture, coronal suture, frontal suture. The fontanelle allows the skull to deform during birth to ease its passage through the birth canal and for expansion of the brain after birth; the anterior fontanelle closes between the ages of 12 and 18 months. The anterior fontanelle is useful clinically. 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. However, this is not a certain indicator for raised pressure as prolonged crying by the baby may produce the same effect. A full anterior fontanelle may be indicative of neonatal meningitis acute bacterial meningitis. Bregma Anatomy image: skel/fetal2 at Human Anatomy Lecture, Pennsylvania State University
The point where the upper temporal line cuts the coronal suture is named the stephanion. This article incorporates text in the public domain from page 183 of the 20th edition of Gray's Anatomy Item #22