What openings are there on the outer base of the skull? External and internal base of the skull
The human skull is the bony base of the head, consisting of twenty-three bones, in addition to which there are three paired bones located in the cavity of the middle ear. The base of the skull consists of that part that is located below the edge that runs in front on the border of the infraorbital margin, behind along the frontal bone, in particular, its zygomatic process, and the infratemporal crest of the bone in the form of a wedge, the upper border of the external auditory canyon, as well as external protrusion of the occiput. External and are distinguished. Today we will look at the internal foundation. But before we begin to study this issue, let us consider what structure and functions the skull has, as well as its shape.
Forms and functions of the skull
The human skull performs several functions:
Protective, which is characterized by the ability to protect the human brain and sensory organs from various damages;
Supportive, consisting in the ability to accommodate the brain and the initial parts of the respiratory and digestive systems;
Motor, characterized by articulation with the spinal column.
The human skull can be represented by one of the following forms: standard (cranial index), acrocephaly (tower-shaped) and craniosynostotic (fusion of the sutures of the cranial vault).
To better understand the anatomy of the skull, let's take a closer look.
Outer base of the skull
This is the customary name for the one that faces down and is covered in front by the bones of the face, and behind the outer base is formed by the bony palate, processes in the form of wings, and medial plates that limit the choanae, separated by the vomer. Behind the pterygoid processes, the base is formed by a wedge-shaped bone, the lower part of the pyramid, the tympanic part, as well as the anterior part of the occipital bone. External base of the skull, anatomical atlas its location will tell you, it has three parts: front, middle and back. Let's look at each of them in more detail.
Posterior section of the base of the outer
In the posterior section there is a vault of the nasopharynx, which is limited by the pharynx. The fascia is attached to the base of the skull, which has a direction from the pharyngeal tubercle to the side, in front of the carotid canal of the pyramid of the temple bone to the lower jaw. In the posterior part of the base there is a large occipital fissure and emissaries that connect the sinuses of the dura mater with the plexus of suboccipital veins, the vertebral vein and the subclavian artery.
Anterior section of the base of the outer
There are gaps here, through which nerves and blood vessels pass. The largest holes, the role of which is very important, are located along the border that connects the stylomastoid fissure and the incisive foramen. The section of the base, which is located in front, includes the bony palate with the incisive and greater palatine canals. The choanae extend backward from the nasal cavity.
Middle section of the outer base
This area includes a torn gap that is located between bones such as the temporal, occipital and sphenoid. There is also a jugular ostium, located between the occipital bone and the temporal bone. In the same area there are such fissures as the sphenoid-petrosal and occipital.
Inner surface of the base of the skull
The base of the skull on the inside contains three fossae: anterior, middle and posterior. According to its location, the anterior fossa is located above the middle one. And this one, in turn, fit above the back one. The cerebrum is located in the first two fossae, and the cerebellum is located in the posterior fossa. The demarcations between the fossae are represented by the edges of the sphenoid bone, which are located behind, as well as the upper level of the pyramids of the temple bones. IN the internal base of the skull is the surface of the skull, which is concave and has irregularities, it repeats the structure of the brain that is adjacent to it. Let's look at its structure in more detail.
Anterior fossa of the skull
The anterior cranial fossa is the deepest. It is formed by the edges of the wings of the bone in the form of a wedge and a protrusion that is located between the visual openings. The frontal sinuses adjoin this fossa in front, and below are the recesses of the ethmoid bone, the nasal cavity and sinuses. In front of the cock's crest there is a blind orifice, through which a small vein follows, which connects the superior sagittal sinus with the nasal veins. On both edges of the ethmoid bone there are olfactory bulbs, where the olfactory nerves enter through the plate from the nasal cavity. Arteries, nerves, and veins also pass through the ethmoid bone to provide the lining of the anterior fossa. IN internal base of the skull involves the placement in this pit of the frontal lobes of the cerebral hemispheres of the human brain.
Middle cranial fossa
The middle cranial fossa is separated from the posterior one with the help of the sella turcica and the tops of the pyramids of the temple bones. In the middle of the fossa there is a sella turcica, which is covered by a diaphragm that has a slit through which a depression appears, which has an ending in the form of a brain appendage. On the diaphragm in front of the funnel there is a chiasm of the optic nerves, on the sides of which there are so-called siphons of the carotid arteries. From them, in turn, the orbital arteries move away; they, together with the optic nerves, pass into the optic canyons. Thus, it involves placement in the middle fossa of the cavernous sinus, which is located away from the sella turcica. The internal carotid artery passes through this place and above the carotid artery, the following nerves are located in the walls of the sinuses: trigeminal, cranial and oculomotor. They pass through the superior opening into the orbit. On the side of these nerves there are veins of the orbits and the eyeball, which then enter the cavernous sinus. Behind the sella turcica, on the vagus nerve, between the sheets of one of the three meninges, the motor nerve is located. Its branches go through the cracks of the round and oval shape of the cranial pit, which is located in the middle. At the back of the form there is a spinous fissure, through which the anterior artery of the dura mater passes into the cranial cavity. It also suggests the presence on both sides of the sella turcica in the fossa, which is located in the middle, of the brain. In front of the inner part of the temple bone, which has the shape of a pyramid, there is a cavity of the middle ear, an intraauricular cavity and a cavity in the mastoid process of the temporal bone.
Posterior cranial fossa
The posterior cranial fossa contains the cerebellum, medulla oblongata and pons. In front of the fossa on the inclined surface there is a bridge, the main artery with all its branches. There is a plexus of veins and stony sinuses. Everything is connected. The posterior fossa is almost entirely occupied by the cerebellum; above and on the sides of it there are sinuses: sigmoid and transverse. The cranial cavity and the posterior fossa are separated by the cerebellar tentorium, through which the brain passes. Let's consider what role it has.
Behind the pyramid of the temple bone is the auditory orifice, through which the facial and auditory nerves and the membranous labyrinth pass. Below the auditory canyon, the glossopharyngeal, accessory nerves, vagus, and also the jugular vein pass through the ragged fissure. If you look below in the atlas, you can see that the hypoglossal nerve and its canal, as well as a plexus of veins, pass through the mouth of the hypoglossal nerve. In the middle of the posterior fossa there is a large occipital fissure, through which the medulla oblongata and its membranes, spinal arteries and the spinal nerve root extend. Along the edge of the groove of the sigmoid sinus, several orifices open into the fossa located behind, allowing emissary veins and the meningeal branch of the occipital artery to pass through. The mouths and slits that connect the posterior fossa with other areas are located in its anterior parts. Thus, they are presented in three types: front, middle and rear.
Finally...
The features of the shape and structure of the human skull cannot be studied without analyzing its functions, just as it is impossible to imagine the functions of any organ without understanding its structure. Knowledge of the anatomy of the skull in medicine is undeniable. This science uses modern diagnostic methods. The structure of the skull was learned through examination, dissection, study, and other things. Today we have the opportunity to study the external thanks to medical atlases that were created many years ago. This knowledge is of particular importance in medical sciences, as it makes it possible to study abnormalities in the development of the skull, the structure of the veins and blood vessels of the brain. Studying the anatomy of the skull is especially important for neurosurgeons, traumatologists and maxillofacial surgeons. Knowledge helps them make the correct diagnosis and prescribe proper treatment in case of various defects or diseases. And this, in turn, can save a person’s life.
Now we know what human scull. Anatomy of the internal base of the skull considered when studying at medical universities. The base is a concave surface, which follows the structure of the brain. It contains many channels and holes and consists of three pits. The inner base of the skull is the surface of the skull where the frontal lobes of the cerebral hemispheres are located, as well as the cerebellum, medulla oblongata and pons. Arteries, vessels, and nerves are also located here. All of them play a huge role in the normal functioning of the human body.
Basis cranii externa
External skull base It is customary to divide into anterior and posterior sections by a line passing through the mastoid processes and the anterior edge of the foramen magnum.
Towards the middle of the back of the anterior section skull base the nasopharynx vault is adjacent, limited by the fascia pharyngobasilaris. The line of attachment of the fascia at the base of the skull is directed from the tuberculum pharyngeum of the occipital bone laterally, then anteriorly from the canalis caroticus of the pyramid of the temporal bone to the spina angularis of the main bone; from here forward and inward along the medial part of the cartilage of the auditory tube, then the fascia crosses the auditory tube from below and is directed to the inner plate of the pterygoid process of the main bone.
Behind and on the sides of the pharynx, from the outer base of the skull, the interpterygoid, stylopharyngeal and prevertebral fascia, which are important in practical terms, begin. The first of them is located between the medial and lateral pterygoid muscles and separates the interpterygoid and parapharyngeal tissue spaces. At the base of the skull, this fascia starts from the fissura petrotympanica (Glaseri), spina angularis, from the medial edges of the spinous and oval foramen and ends on the outer plate of the pterygoid process.
Rice. 1. Varieties of the external base of the skull (photo).
On the right - dolichocephalic (cranial index 68.3); on the left - brachycephalic (cranial index 89.6).
The stylopharyngeal fascia separates the posterior part of the parapharyngeal space from the anterior one, and outside and in front - from the parotid gland. The fascia starts from the lateral wall of the pharynx, and at the base of the skull it is attached in front of the canalis caroticus, then along the bone crest, limiting the canalis caroticus and fossa jugularis in front and outside, to the styloid process, and from it along the bone crest to the mastoid process.
The stylopharyngeal fascia is pierced by the thin nerves of the pharyngeal plexus and the branches of the ascending pharyngeal artery, heading to the lateral wall of the pharynx and the soft palate. In 21% of cases, the ascending pharyngeal artery pierces the fascia at the base of the skull, which then goes to the soft palate. These vessels and nerves connect the anterior and posterior parapharyngeal spaces.
Another feature of the anterior section of the external base of the skull is that the main part of the openings through which vessels and nerves pass are located here, and the largest and most important openings (foramen lacerum, the beginning of the canalis caroticus, foraminis spinosum and ovale) are located along the line connecting the incisive and the stylomastoid foramen, or in its immediate vicinity.
In the posterior part of the outer base of the skull there is the foramen magnum and several emissaries (vv. emissariae condyloidea, occipitalis and plexus venosus canalis hypoglossi), connecting the sinuses of the dura mater with the plexus venosus suboccipitalis, vv. vertebralis and cervicalis profunda.
Rice. 2. Vessels, nerves and fascial layers located on the outer base of the skull (2/3).
The hard and soft palate and alveolar process were removed and the nasal cavity and pharyngeal vault were opened. On the left, the maxillary cavity was opened, the branch of the lower jaw was sawn and the masticatory and temporal muscles were crossed, the parotid gland and muscles were removed from their fascial sheaths; on the right - the lower wall and contents of the orbit, the pterygoid process and almost all the muscles and tissue down to the bone were removed.
| External base of the skull(basis cranii extema). View from below. 1st palatine process of the maxilla; |
The occipital bone, posterior surfaces of the pyramids, and temporal bones take part in the formation of the posterior cranial fossa.
Between the back of the sella turcica and the foramen magnum there is a clivus.
The internal auditory foramen (right and left) opens into the posterior cranial fossa, from which the vestibulocochlear nerve (VIII pair) emerges, and from the facial nerve canal - the facial nerve (VII pair). The lingual pharyngeal (IX pair), vagus (X pair) and accessory (XI pair) nerves exit through the jugular foramen of the base of the skull. The nerve of the same name, the XII pair, passes through the canal of the hypoglossal nerve. In addition to the nerves, the internal jugular vein emerges from the cranial cavity through the jugular foramen, which passes into the sigmoid sinus. The formed foramen magnum connects the cavity of the posterior cranial fossa with the spinal canal, at the level of which the medulla oblongata passes into the spinal cord.
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The outer base of the skull (basis cranii extema) in its anterior section is covered by the facial bones (it contains a bony palate, limited in front by the alveolar process of the upper jaw and teeth), and the posterior section is formed by the outer surfaces of the sphenoid, occipital and temporal bones
This area has a large number of openings through which vessels and nerves pass, providing blood supply to the brain. The central part of the external base of the skull is occupied by the foramen magnum, on the sides of which there are the occipital condyles. The latter connect to the first vertebra of the cervical spine. The exit from the nasal cavity is represented by paired openings (choanae), which pass into the nasal cavity. In addition, on the outer surface of the base of the skull there are the pterygoid processes of the sphenoid bone, the external opening of the carotid canal, the styloid process, the stylomastoid foramen, the mastoid process, the myotubal canal, the jugular foramen and other formations.
In the skeleton of the facial skull, the central place is occupied by the nasal cavity, orbits, oral cavity, infratemporal and pterygopalatine fossa
Outer base of the skull basis cranii externa, covered in front by facial bones.
Almost in the center of this area there is a large occipital foramen, and on its sides there are occipital condyles.
Behind each condyle there is a condylar fossa with a non-permanent opening - the condylar canal.
Anterior to the foramen magnum lies the basilar part of the occipital bone with a well-defined pharyngeal tubercle.
The basilar part passes into the body of the sphenoid bone. On each side of the occipital bone, on each side, the lower surface of the pyramid of the temporal bone is visible, on which the following important formations are located: the external opening of the carotid canal, the muscular-tubal canal, the jugular fossa and the jugular notch, which with the jugular notch of the occipital bone forms the jugular foramen, the styloid process , mastoid process, and between them the stylomastoid foramen.
Adjacent to the pyramid of the temporal bone on the lateral side is the tympanic part of the temporal bone, surrounding the external auditory opening. Posteriorly, the tympanic part is separated from the mastoid process by the tympanomastoid fissure. On the posteromedial side of the mastoid process are the mastoid notch and the groove of the occipital artery.
On a horizontally located section of the squamous part of the temporal bone there is a mandibular fossa, which serves for articulation with the condylar process of the lower jaw. In front of this fossa is the articular tubercle. In the gap between the petrous and scaly parts of the temporal bone on the whole skull, the posterior part of the large wing of the sphenoid bone enters; the foramen spinosum and foramen ovale are clearly visible here. The pyramid of the temporal bone is separated from the occipital bone by the petrooccipital fissure, fissura petrooccipitalis, and from the greater wing of the sphenoid bone by the sphenoid-petrosal fissure, fissura sphenopetrosa. In addition, on the lower surface of the outer base of the skull, a hole with uneven edges is visible - a ragged hole, foramen lacerum, limited laterally and posteriorly by the apex of the pyramid, which is wedged between the body of the occipital and the greater wing of the sphenoid bones.
The bones of the skull, connecting with each other, form a large number of cavities, depressions and pits.
On the brain skull there is an upper part - the roof of the skull and a lower part - the base of the skull.
The roof of the skull is composed of the parietal bones, partly the frontal, occipital and temporal bones. The base of the skull is formed by the orbital parts of the frontal bone, the ethmoid, sphenoid, temporal, and occipital bones.
By separating the roof of the skull, you can study the internal base of the skull, which is divided into three cranial fossae: anterior, middle and posterior. The anterior cranial fossa is formed by the orbital part of the frontal bone, the cribriform plate of the ethmoid bone and the lesser wings of the sphenoid bone; the middle cranial fossa - mainly the cerebral surface of the large wings of the sphenoid bone, the upper surface of its body, as well as the anterior surface of the pyramid of the temporal bone; posterior cranial fossa - the occipital bone and the posterior surface of the petrous part of the temporal bone.
The frontal lobes of the cerebral hemispheres are located in the anterior cranial fossa, the temporal lobes in the middle, and the cerebellum, pons and medulla oblongata in the posterior cranial fossa. Each hole has a series of holes. The anterior cranial fossa has openings of the cribriform plate, connecting it with the nasal cavity. From the middle cranial fossa, the superior orbital fissure and the optic canal lead into the orbital cavity; the round hole leads into the pterygopalatine fossa and through it into the orbit; The foramen ovale and spinous foramen communicate the middle cranial fossa with the outer base of the skull. In the posterior cranial fossa there are several openings: the large one (occipital), which connects the cranial cavity with the spinal canal; jugular, leading to the outer surface of the base of the skull, and internal auditory, leading to the inner ear.
Looking at the skull from below, you can see that the base of the skull in its anterior section is covered by the bones of the face, which form the bony palate, consisting of the palatine processes of the upper jaws and palatine bones. In the middle and posterior sections, the base of the skull is formed by the lower surfaces of the sphenoid, occipital and temporal bones. They have a large number of foramina, in particular the jugular foramen between the occipital and temporal bones and the ragged foramen between the petrous part of the temporal bone and the sphenoid bone.
The largest topographic-anatomical formations of the facial skull are the orbit, nasal and oral cavities.
The eye socket has the shape of a tetrahedral pyramid. Its medial wall is formed by the frontal process of the maxilla, the lacrimal bone, the orbital plate of the ethmoid bone and partly the body of the sphenoid bone; the upper wall - the orbital part of the frontal bone, the small wings of the sphenoid bone; lateral wall - large wings of the sphenoid bone and zygomatic bone; the lower wall is the upper surface of the body of the upper jaw. The orbit communicates with the cranial cavity through the superior orbital fissure and the optic canal; from the nasal - through the nasolacrimal canal formed by the lacrimal bone, the frontal process of the upper jaw and the inferior nasal concha; with the infratemporal and pterygopalatine fossae - using the lower orbital fissure, which is located between the large wings of the sphenoid bone and the body of the upper jaw.
The nasal cavity has upper, lower and lateral walls. It is divided by a bony septum located in the median plane. The septum is formed by the perpendicular plate of the ethmoid bone and the vomer. The upper wall of the nasal cavity is formed by the cribriform plate of the ethmoid bone, as well as the nasal and frontal bones; the lower wall - the palatine process of the upper jaw and the horizontal plate of the palatine bone; lateral walls - the upper jaw, the lacrimal and ethmoid bones, the inferior nasal concha, the perpendicular plate of the palatine bone and the medial surface of the pterygoid process of the sphenoid bone. The anterior opening of the nasal cavity, called the pyriform opening, communicates it with the environment; the posterior openings, choanae, face the outer base of the skull and connect the nasal cavity with the pharyngeal cavity.
The nasal cavity on the right and left is divided by the nasal conchae, located on its lateral wall, into three passages: lower, middle and upper. All of them are connected to each other by a common nasal passage located on the sides of the nasal septum. The nasal cavity communicates with the cavity of the skull, orbit, nasal and oral cavities, and the air sinuses. The upper nasal meatus communicates with the cranial cavity through the openings of the cribriform plate of the ethmoid bone, the middle one with the sinus of the upper jaw, with the cells of the ethmoid bone and with the frontal sinus. Posteriorly, at the level of the superior turbinate, the sinus of the sphenoid bone opens into the nasal cavity. The inferior nasal meatus communicates with the orbital cavity through the nasolacrimal duct. The nasal cavity also communicates with the pterygopalatine fossa through the sphenopalatine foramen and with the oral cavity through the incisive foramen.
The oral cavity is limited by bony walls only from above, in front and from the sides. Its upper wall is formed by the bony palate, composed of the palatine processes of the right and left upper jaws and the horizontal plates of the palatine bones; the lateral and anterior walls are formed by the lower jaw and the alveolar processes of the upper jaws. The oral cavity communicates through the incisive foramen with the nasal cavity, and through the greater palatine canal with the pterygopalatine fossa.
On the lateral surface of the skull there are the pterygopalatine, infratemporal and temporal fossae.
The pterygopalatine fossa is located between the bones of the facial and cerebral skull and is limited in front by the body of the upper jaw, on the medial side by the palatine bone, behind by the pterygoid process of the sphenoid bone, and above by the body of this bone. It communicates with the nasal cavity, the middle cranial fossa, the foramen lacerum, the orbit and the oral cavity. The pterygopalatine fossa does not have a lateral wall and extends outward into the infratemporal fossa.
The infratemporal fossa is located posterior to the body of the upper jaw, inward from the zygomatic bone and zygomatic arch and externally from the pterygoid process of the sphenoid bone. It forms part of the outer base of the skull. It is separated from the temporal fossa by the infratemporal crest.
The temporal fossa is a flat depression in which the temporalis muscle lies. The formation of the temporal fossa involves the temporal surface of the large wings of the sphenoid bone, the squama of the temporal bone, and partly the parietal and frontal bones.
