The exterior surface of the base of the skull, not included the mandible, is bounded in prior by the incisor teeth of the maxillae, behind through the superior nuchal currently of the occipital bone, and laterally by the remaining teeth, the zygomatic arch and also its posterior root, and also the base of the mastoid process.It is very irregular and, unlike the internal surface, reflects no organic subdivision into regions perfect for descriptive purposes. That is, however, both usual and also useful to divide the area right into anterior, middle and also posterior parts. The anterior part, i beg your pardon is developed by the tough palate and also the alveolar arches, projects downwards to a lower level than the component behind. The remainder of the surface ar is divided, in an arbitrary manner, right into a middle and a posterior component by a transverse line attracted through the anterior margin of the foramen magnum.
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The floor the the articular fossa is an extremely thin and corresponds to the many lateral part of the floor of the middle cranial fossa. It is extended in the current state by white ftbro-cartilage. The tubercle the the root of the zygoma offers attachment come the ternporoinandibniar ligament. A slim edge of bone may be clearly shows in the depth of the medial end of the squamotympanic fissure. It is the reduced border of the down-turned lateral section of the tegmen tympani and therefore is a component of the petrous temporal.
It divides the upper component of the squamotympanic fissure into a petrotympanic and also a petrosquamous fissure. V the former the chorda tympani travel in its anterior canaliculus, together it passes downwards and forwards native the tympanic cavity. The anterior tympanic artery native the maxillary (internal maxillary) artery likewise traverses the petrotympanic fissure.
The tympanic part of the temporal bone (fig. 325) is separated from the capsule the the temporomandibular share by a part of the parotid gland, i m sorry is pierced through the auriculotemporal nerve. That is thinnest near the center of this surface and also is sometimes deficient in this instance (p. 300). The grooved upper element of the plate develops the anterior wall, the floor and also the lower part of the posterior wall of the exterior auditory meatus. Other than where that ensheathes the styloid process its posterior facet is fused v the petrous component of the bone.
THE POSTERIOR part OF THE NORMA BASALIS (fig. 322)
The median portion of the posterior subdivision that the external surface that the basic of the skull is inhabited in former by the foramen magnum that the occipital bone, i beg your pardon leads right into the floor that the posterior cranial fossa. The foramen is somewhat oval in shape and its anteroposterior above its transverse measurement. The curve of its margin is more comprehensive behind 보다 in front. It transmits a huge number of frameworks of i m sorry the most necessary is the lower finish of the brain-stem. Anteriorly the margin the the foramen magnum is overlapped slightly on every side through the occipital condyle, which tasks downwards come articulate through the remarkable articular facet on the lateral mass of the atlas. Oval in outline, the condyle is inserted obliquely so that its anterior end is nearer to the median aircraft than that is posterior end. It mirrors a express convexity from prior to backwards and also a gentle convexity from next to side. The medial element is roughened for ligamentous attachments. Over the anterior part of the condyle the occipital bone is pierced by the anterior condylar (hypoglossal) canal, which operation laterally and slightly forwards from the posterior cranial fossa and also transmits the hypoglossal nerve.
A depression of change depth point out the occipital bone behind the condyle. The is termed the condylar fossa, and also its floor may be pierced by the posterior condylar canal, which, once present, transmits an emissary vein native the sigmoid sinus. Lateral to the condyle the jugular procedure of the occipital bone articulates through the petrous temporal. The anterior border that the process is complimentary and creates the posterior boundary of the jugular foramen. This foramen lies between the occipital bone and the jugular fossa of the petrous temporal and is inserted at the posterior end of the petro-occipital suture. In front it is separated indigenous the lower orifice the the carotid canal through a raised ridge that bone, and also on that is lateral side it is concerned the medial element of the sheath that the styloid process. Medially the is separated native the anterior condylar (hypoglossal) canal by a thin bar that bone. The foramen is usually bigger on the appropriate side the the skull and its long axis is directed forwards and also medially. The anterior component of the foramen transmits the inferior petrosal sinus ; its intermediate part, the glossopharyngeal, vagus and accessory nerves ; and its posterior part the internal jugular vein. Once the premium bulb that the inner jugular vein is well developed the jugular fossa of the temporal bone is hollowed out in one upward and also lateral direction come accommodate it.
The styloid process has been described above. Posterior to its root the stylomastoid foramen, which to represent the lower opening that the face canal, transmits the face nerve. Behind and also lateral to the foramen the reminder of the mastoid process projects downwards and forwards, and its projecting part forms the lateral wall surface of the mastoid (digastric) notch, native which the posterior ship of the digastric muscle take away origin. Medial come the notch this part of the temporal bone might be grooved by the occipital artery.
In the median aircraft posteriorly the squamous part of the occipital bone presents the outside occipital crest, which offers attachment to the upper end of the ligamentum nuchae. That terminates behind in ~ the exterior occipital protuberance. Close to its midpoint the inferior nuchal line curves backwards and also laterally, about parallel to the remarkable nuchal line, i m sorry extends in the exact same direction native the exterior occipital protuberance and also may be raised into a unique crest in its medial part.
Particular features.-The foramen magnum offers a large communication in between the posterior cranial fossa and the vertebral canal. Anteriorly the transmits the apical ligament of the odontoid procedure (dens) and also the membrana tectoria, both that which obtain attachment to the upper or cerebral surface of the basilar component of the occipital bone. Its wider posterior part transmits the lower end of the medulla oblongata and also the meninges. In the subarachnoid space the spinal root; the the accessory nerves, and the vertebral arteries, through their plexuses of forgiveness nerves, ascend to acquire the inner of the cranium, the posterior spinal arteries descend, one on every posterolateral aspect of the mind stem, and also the anterior spinal artery- descends on the front. The the mind stem in the typical plane. In addition, the reduced parts that the tonsils of the cerebellum may project right into the foramen on every side of the medulla oblongata. The. Anterior margin the the foramen provides attachment come the anterior atlanto-occipital membrane, i m sorry is consistent on each side through the capsular ligament of the atlanto-occipital joint. The posterior margin gives attachment come the posterior atlanto-occipital membnme, and the roughened medial facet of the condyle come the alar ligament. In enhancement to the hypoglossal nerve the anterior condylar (hypoglossal) canal transmits a meningeal branch that the ascending pharyngeal artery and also a tiny emissary vein native the basilar plexus. Not uncommonly the canal is split into two parts by a spicule of bone, a sports wbich is in keeping with the composite origin of the hypoglossal nerve. The inferior surface of the jugular procedure of the occipital bone provides insertion because that the rectus capitis lateralis muscle.
The jugular foramen (fig. 322) is directed upwards, medially and backwards, and also on .the external surface that the base of the skull its apparent size is boosted owing to the presence of the jtzaular fossa of the temporal bone ~ above its lateral side. The floor the the fossa .separates the exceptional bulb the the interior jugular vein from the tvmpanic cavity, and also its lateral wall is pierced by a minute canal, termed the mastoid canaliculus, i beg your pardon transmits the auricular branch of the vagus nerve. Passing laterally through the bone this nerve comes right into intimate relationship with the face canal and also finally increase in the heat of the fympanomastoid suture. That is extra-cranial in ~ birth yet becomes surrounded by bone together the tympanic plate and the mastoid procedure develop. On or near the ridge i beg your pardon intervenes in between the jugular fossa and the orifice of the carotid canal, the canaliculus, because that the tympanic nerve pierces the bone come transmit. The tympanic nerve native the glossopharyngeal nerve to the middle ea.r. ~ above the top boundary of the jugular foramen close to its medial end, there is a small notch-more easily figured out on the internal surface-which lodges the inferior (petrous) ganglion that the glossopharyngeal nerve. The orifice that the cochlear canaliculus (p. 297) lies at the apex of the notch, the projecting edge of which may reach the occipital bone and divide the foramen right into three parts.
The stylomastoid foramen lies behind the basic of the styloid process and at the anterior finish of the mastoid notch. Together the face nerve increase from the foramen that is in nearby proximity to the posterior ship of the digastric, which the supplies prior to piercing the parotid kind. In addition to the facial nerve the foramen transmits the stylornastoid branch the the posterior auricular artery. A vascular groove crosses the inferior facet of the mastoid component of the temporal bone medial come the mastoid notch. The is brought about by the occipital artery and also its absence indicates the the ship lay at a lower level 보다 usual and also between the splenius capitis and also longissimus capitis instead of deep to both muscles.
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The area listed below the inferior nuchal line offers insertion medially to the rectus capitis posterior minor, and also laterally come the rectus capitis posterior significant (fig. 345). The interval in between the inferior and the superior nuchal lines offers insertion medially because that the semispinalis capitis and also laterally because that the obliquus superior. In the medial part the superior nuchal line provides origin come the greatest fibers of the trapezius muscle; in that is lateral part it gives insertion to yarn of the sternomastoid and, much more anteriorly, splenius capitis.