Occipital bone. Human Occipital Bone Anatomy - Information

The occipital bone, os occipitalae, is unpaired, making up the back of the base and roof of the skull. It distinguishes four parts: the main, pars basilaris, two lateral, partes laterales, and scales, squama. In a child, these parts are separate bones connected by cartilage. On the 3rd - 6th year of life, the cartilage ossifies and they fuse together into one bone. All these parts join together to form a large opening, the foramen magnum. In this case, the scales lie behind this hole, the main part is in front, and the lateral ones are on the sides. The scales are mainly involved in the formation of the posterior part of the skull roof, and the main and lateral parts are the base of the skull.
The main part of the occipital bone has the shape of a wedge, the base of which is turned forward to the sphenoid bone, and the tip is posterior, limiting the large opening in front. In the main part, five surfaces are distinguished, of which the upper and lower are connected behind at the anterior edge of the occipital foramen. The anterior surface is connected by the sphenoid bone until the age of 18 - 20 with the help of cartilage, which subsequently ossifies. The upper surface - slope, clivus, is concave in the form of a groove, which is located in the sagittal direction. The medulla oblongata, pons, blood vessels and nerves are adjacent to the slope. In the middle of the lower surface is the pharyngeal tubercle, tuberculum pharyngeum, to which the initial part of the pharynx is attached. On the sides of the pharyngeal tubercle, two transverse ridges extend from each side, of which m is attached to the anterior one. longus capitis, and to the back - m. rectus capitis anterior. Lateral rough surfaces of the main part are connected by means of cartilage to the petrous part of the temporal bone. On their upper surface, near the lateral edge, there is a small groove of the lower petrosal sinus, sulcus sinus petrosi inferioris. It is in contact with a similar groove in the petrous part of the temporal bone and serves as a place to which the inferior petrosal venous sinus of the dura is adjacent.
The lateral part is located on both sides of the foramen magnum and connects the main part to the scales. Its medial edge faces the foramen magnum, the lateral edge faces the temporal bone. The lateral edge carries the jugular notch, incisura jugularis, which, with the corresponding notch of the temporal bone, limits the jugular foramen. The intrajugular process, processus intrajugularis, located along the edge of the notch of the occipital bone, divides the opening into anterior and posterior. The internal jugular vein passes in the anterior, and the IX, X, IX pairs of cranial nerves pass in the posterior. The back of the jugular notch is limited by the base of the jugular process, processus jugularis, which faces the cranial cavity. Behind and inside of the jugular process on the inner surface of the lateral part is a deep groove of the transverse sinus, sulcus sinus transverse. In the anterior part of the lateral part, on the border with the main part, there is a jugular tubercle, tuberculum jugulare, and on the lower surface there is an occipital condyle, condylus occipitalis, with which the skull articulates with the I cervical vertebra. The condyles, according to the shape of the upper articular surface of the atlas, form oblong ridges with convex oval articular surfaces. Behind each condyle there is a condylar fossa, fossa condylaris, at the bottom of which there is a visible opening of the outlet canal connecting the veins of the meninges with the external veins of the head. This hole is absent in half of the cases on both sides or on one side. Its width is highly variable. The base of the occipital condyle is pierced by the hypoglossal nerve canal, canalis hypoglossi.
The occipital scales, squama oscipitalis, are triangular in shape, curved, its base facing the occipital foramen, the apex facing the parietal bones. The upper edge of the scales is connected by the parietal bones through a lambdoid suture, and the lower edge is connected to the mastoid parts of the temporal bones. In this regard, the upper edge of the scales is called lambdoid, margo lambdoideus, and the lower edge is mastoid, margo mastoideus. The outer surface of the scales is convex, in its middle there is an external occipital protrusion, protuberantia occipitalis externa, from which the external occipital crest, crista occipitalis externa, descends vertically down towards the occipital foramen, intersecting in pairs with two nuchal lines, lineae nuchae superior et inferior. In some cases, the highest nuchal line, lineae nuchae suprema, is also noted. Muscles and ligaments are attached to these lines. The inner surface of the occipital scale is concave, forming in the center an internal occipital protrusion, protuberantia occipitalis interna, which is the center of the cruciform eminence, eminentia cruciformis. This elevation divides the inner surface of the scale into four separate depressions. The occipital lobes of the brain adjoin the two upper ones, and the hemispheres of the cerebellum adjoin the two lower ones.
Ossification. It begins at the beginning of the 3rd month of intrauterine development, when islands of ossification appear both in the cartilaginous and connective tissue parts of the occipital bone. In the cartilaginous part, five ossification points arise, of which one is located in the main part, two in the lateral parts, and two in the cartilaginous part of the scale. Two ossification points appear in the connective tissue upper part of the scale. By the end of the 3rd month, the fusion of the upper and lower sections of the scales occurs; in the 3rd-6th year, the main part, lateral parts and scales grow together.

Forms the posterior part of the brain skull. It distinguishes the basilar (main) part, the lateral parts and the occipital scales. All these parts surround a large occipital foramen, foramen magnum, through which the cranial cavity communicates with the spinal canal.

Basilar part located in front of the foramen magnum. By the age of 18-20, it fuses with the body of the sphenoid bone into one whole. The cerebral surface of the basilar part has the shape of a gutter and, together with the body of the sphenoid bone, forms a platform inclined towards the large occipital foramen - the slope. The sulcus of the inferior stony sinus runs along the lateral edge of the basilar part. On the lower surface of the basilar part there is a well-defined pharyngeal tubercle.

Lateral part the steam room, has an irregular shape and, gradually expanding, posteriorly passes into the occipital scales. On the lower surface of each lateral part is a well-defined ellipsoidal occipital condyle. The condyles, with their convex surfaces, are connected to the superior articular fossae of the atlas. Through each lateral part above the condyle passes the hypoglossal canal, in which the hypoglossal nerve passes. Immediately behind the occipital condyle is the condylar fossa. At the bottom of it there is a hole for a venous graduate - the condylar canal. Lateral to the occipital condyle there is a jugular notch. Behind this notch is limited by the jugular process directed upwards. A well-defined groove of the sigmoid sinus passes near the process on the cerebral surface of the lateral part.

Occipital scales It is a wide plate with a concave inner surface and a convex outer one. In the center of the outer surface there is an external occipital protrusion (tubercle), from which the external occipital crest descends down the midline to the posterior edge of the foramen magnum. From the occiput to the right and to the left there is a curved downward upper nuchal line. Parallel to the latter, approximately at the level of the middle of the external occipital crest, an inferior nuchal line extends from it in both directions. In addition, there is a less noticeable highest nuchal line above the external occipital protrusion.

On the inner, cerebral, surface of the occipital scales there is a cruciform elevation formed by furrows that divide the cerebral surface of the scales into 4 pits. The center of the cruciform eminence protrudes forward and forms an internal occipital protrusion. At the level of the ledge to the right and to the left there is a groove of the transverse sinus, passing into the groove of the sigmoid sinus. Above the internal occipital protrusion is the groove of the superior sagittal sinus, which continues into the groove of the same name in the parietal bone. From top to bottom, the internal occipital protrusion narrows and continues as an internal occipital crest, which reaches the foramen magnum. The edges (lambdoid and mastoid) of the upper and lateral parts of the occipital scales are strongly serrated, in these places the occipital bone is connected to the parietal and temporal bones.

occipital scales, squama occipitalis, limits the large occipital foramen posteriorly.

On its outer surface, there are: inion, inion(point corresponding to the external occipital protrusion); lower, upper and highest protruding lines ( linea nuchalis inferior, superior et suprema); external occipital crest, Crista occipitalis externa.

On the inner surface of the occipital scales are distinguished: internal occipital protrusion, protuberantia occipitalis interna; internal occipital crest, crista occipitalis interna; sulcus of the superior sagittal sinus sulcus sinus sagittalis superioris; groove of the transverse sinus (right and left), sulcus sinus transverse; sulcus of the sigmoid sinus (near the jugular notch), sulcus sinus sigmoidei; sulcus of the occipital sinus, sulcus sinus occipitalis.

The internal relief corresponds to the venous sinuses and separates the two upper, cerebral and two lower, cerebellar fossas.

Lateral part (right and left), pars lateralis, located on the side of the foramen magnum foramen magnum. It includes the occipital condyle (right and left), condilus occipitalis, convex and oblique anteriorly and medially. True rotation is carried out here, the condyles glide in all directions. Condylar canal containing the emissary vein. Hyoid canal, oblique anteriorly, perpendicular to the condyle and containing the hypoglossal nerve. Lateral to the jugular foramen is the jugular process, oriented outwards. The jugular process corresponds to the transverse process of C1. The jugular processes are involved in the formation of petro-jugular synchondrosis, which, presumably, ossifies at 5-6 years of age. The internal jugular vein passes through the jugular foramen, through which approximately 95% of the venous blood from the skull is drained. Thus, with blockade of the petro-jugular suture, cephalgia of venous stasis may occur.

Basilar part of the occipital bone, pars basilaris, located anterior to the large opening, square in shape, sloping from top to bottom and from front to back. On the lower (outer) surface of the basilar part is the pharyngeal tubercle, tuberculum pharyngeum. The beginning of the laryngo-esophago-pharyngeal fascia, which is a tube surrounding the neck formations of the same name, is attached to the pharyngeal tubercle. Osteopaths call it the central ligament, it extends to the thoracic diaphragm. The result of its downward tension may be the straightening of the cervical lordosis (reciprocal tension of the nuchal ligament), and one of the possible causes will be gastric dysfunction. On the upper (inner) surface, a slope is determined, clivus, basion (a point corresponding to the middle of the anterior margin of the foramen magnum), two lateral margins articulating with the pyramids of the temporal bones, and an anterior margin articulating with the body of the sphenoid bone.

Rice. Occipital bone (according to H. Feneis, 1994): 1 - large occipital foramen; 2 - basion; 3 - condylar part; 4 - scales of the occipital bone; 5 - mastoid edge; 6 - parietal edge; 7 - occipital condyle; 8 - condylar canal; 9 - canal of the hypoglossal nerve; 10 - jugular process; 11 - intrajugular process; 12 - external occipital protrusion (inion); 13 - cruciform elevation; 14 - internal occipital protrusion; 15 - furrow of the superior sagittal sinus; 16 - groove of the transverse sinus; 17 - groove of the sigmoid sinus.

The occipital bone (os occipitale) (Fig. 59) is unpaired, located in the posterior part of the brain skull and consists of four parts located around a large hole (foramen magnum) (Fig. 60, 61, 62) in the anteroinferior section of the outer surface.

The main, or basilar, part (pars basilaris) (Fig. 60, 61) lies anterior to the external opening. In childhood, it connects to the sphenoid bone with the help of cartilage and forms a wedge-occipital synchondrosis (synchondrosis sphenooccipitalis), and in adolescence (after 18-20 years) the cartilage is replaced by bone tissue and the bones grow together. The upper inner surface of the basilar part, facing the cranial cavity, is slightly concave and smooth. It contains part of the brain stem. At the outer edge there is a groove of the lower petrosal sinus (sulcus sinus petrosi inferior) (Fig. 61), adjacent to the posterior surface of the petrous part of the temporal bone. The lower outer surface is convex and rough. In the center of it is the pharyngeal tubercle (tuberculum pharyngeum) (Fig. 60).

Lateral, or lateral, part (pars lateralis) (Fig. 60, 61) steam room, has an elongated shape. On its lower outer surface is an elliptical articular process - the occipital condyle (condylus occipitalis) (Fig. 60). Each condyle has an articular surface, through which it articulates with the I cervical vertebra. Behind the articular process is the condylar fossa (fossa condylaris) (Fig. 60) with the non-permanent condylar canal (canalis condylaris) lying in it (Fig. 60, 61). At the base, the condyle is pierced by the hypoglossal canal (canalis hypoglossi). On the lateral edge is the jugular notch (incisura jugularis) (Fig. 60), which, combined with the same notch of the temporal bone, forms the jugular foramen (foramen jugulare). The jugular vein, glossopharyngeal, accessory and vagus nerves pass through this opening. On the posterior edge of the jugular notch is a small protrusion called the jugular process (processus intrajugularis) (Fig. 60). Behind him, along the inner surface of the skull, there is a wide groove of the sigmoid sinus (sulcus sinus sigmoidei) (Fig. 61, 65), which has an arcuate shape and is a continuation of the temporal bone groove of the same name. Anterior to it, on the upper surface of the lateral part, there is a smooth, gently sloping jugular tubercle (tuberculum jugulare) (Fig. 61).

The most massive part of the occipital bone is the occipital scales (squama occipitalis) (Fig. 60, 61, 62), located behind the large occipital foramen and taking part in the formation of the base and vault of the skull. In the center, on the outer surface of the occipital scales, there is an external occipital protrusion (protuberantia occipittalis externa) (Fig. 60), which is easily palpable through the skin. From the external occipital protrusion to the large occipital foramen, the external occipital crest (crista occipitalis externa) is directed (Fig. 60). Paired upper and lower nuchal lines (linea nuchae superiores et inferiores) (Fig. 60) depart from the external occipital crest on both sides, which are a trace of muscle attachment. The upper protruding lines are at the level of the outer protrusion, and the lower ones are at the level of the middle of the outer ridge. On the inner surface, in the center of the cruciform eminence (eminentia cruciformis), there is an internal occipital protrusion (protuberantia occipittalis interna) (Fig. 61). Down from it, up to the large occipital foramen, the internal occipital crest (crista occipitalis interna) descends (Fig. 61). A wide flat groove of the transverse sinus (sulcus sinus transversi) is directed to both sides of the cruciform eminence (Fig. 61); the furrow of the superior sagittal sinus (sulcus sinus sagittalis superioris) goes vertically upwards (Fig. 61).

The occipital bone is connected to the sphenoid, temporal and parietal bones.

The sphenoid bone (os sphenoidale) (Fig. 59) is unpaired, located in the center of the base of the skull. In the sphenoid bone, which has a complex shape, the body, small wings, large wings and pterygoid processes are distinguished.

The body of the sphenoid bone (corpus ossis sphenoidalis) has a cubic shape, six surfaces are distinguished in it. The upper surface of the body faces the cranial cavity and has a depression called the Turkish saddle (sella turcica), in the center of which is the pituitary fossa (fossa hypophysialis) with the lower appendage of the brain, the pituitary gland, lying in it. In front, the Turkish saddle is limited by the tubercle of the saddle (tuberculum sellae) (Fig. 62), and behind it by the back of the saddle (dorsum sellae). The posterior surface of the body of the sphenoid bone is connected to the basilar part of the occipital bone. On the front surface there are two openings leading to the airy sphenoid sinus (sinus sphenoidalis) and called the aperture of the sphenoid sinus (apertura sinus sphenoidalis) (Fig. 63). The sinus is finally formed after 7 years inside the body of the sphenoid bone and is a paired cavity separated by the septum of the sphenoid sinuses (septum sinuum sphenoidalium), which emerges on the front surface in the form of a sphenoid ridge (crista sphenoidalis) (Fig. 63). The lower section of the crest is pointed and is a wedge-shaped beak (rostrum sphenoidale) (Fig. 63), wedged between the wings of the vomer (alae vomeris), which is attached to the lower surface of the body of the sphenoid bone.

Small wings (alae minores) (Fig. 62, 63) of the sphenoid bone are directed in both directions from the anteroposterior corners of the body and represent two triangular plates. At the base, the small wings are pierced by the optic canal (canalis opticus) (Fig. 62), which contains the optic nerve and the ophthalmic artery. The upper surface of the small wings faces the cranial cavity, and the lower surface takes part in the formation of the upper wall of the orbit.

Large wings (alae majores) (Fig. 62, 63) of the sphenoid bone move away from the side surfaces of the body, heading outward. At the base of the large wings there is a round hole (foramen rotundum) (Fig. 62, 63), then an oval (foramen ovale) (Fig. 62), through which the branches of the trigeminal nerve pass, and outwards and backwards (in the region of the wing angle ) there is a spinous opening (foramen spinosum) (Fig. 62), passing the artery that feeds the hard shell of the brain. The inner, cerebral, surface (facies cerebralis) is concave, and the outer one is convex and consists of two parts: the orbital surface (facies orbitalis) (Fig. 62), which is involved in the formation of the walls of the orbit, and the temporal surface (facies temporalis) (Fig. 63) involved in the formation of the wall of the temporal fossa. Large and small wings limit the upper orbital fissure (fissura orbitalis superior) (Fig. 62, 63), through which blood vessels and nerves enter the orbit.

Pterygoid processes (processus pterygoidei) (Fig. 63) depart from the junction of large wings with the body and go down. Each process is formed by the outer and inner plates, fused in front, and diverging behind and limiting the pterygoid fossa (fossa pterygoidea).

The inner medial plate of the pterygoid process (lamina medialis processus pterygoideus) (Fig. 63) takes part in the formation of the nasal cavity and ends with a pterygoid hook (hamulus pterygoideus) (Fig. 63). The outer lateral plate of the pterygoid process (lamina lateralis processus pterygoideus) (Fig. 63) is wider, but less long. Its outer surface faces the infratemporal fossa (fossa infratemporalis). At the base, each pterygoid process is pierced by the pterygoid canal (canalis pterygoideus) (Fig. 63), through which the vessels and nerves pass.

The sphenoid bone is connected to all the bones of the brain skull.

The temporal bone (os temporale) (Fig. 59) is paired, takes part in the formation of the base of the skull, lateral wall and arch. It contains the organ of hearing and balance (see the "Sense Organs" section), the internal carotid artery, part of the sigmoid venous sinus, the vestibulocochlear and facial nerves, the trigeminal ganglion, the branches of the vagus and glossopharyngeal nerves. In addition, connecting with the lower jaw, the temporal bone serves as a support for the masticatory apparatus. It is divided into three parts: stony, scaly and drum.

The stony part (pars petrosa) (Fig. 65) has the shape of a tripartite pyramid, the top of which is facing anteriorly and medially, and the base, which passes into the mastoid process (processus mastoideus), is posteriorly and laterally. On the smooth front surface of the stony part (facies anterior partis petrosae), near the top of the pyramid, there is a wide depression, which is the site of the adjacent trigeminal nerve, the trigeminal depression (impressio trigemini), and almost at the base of the pyramid there is an arcuate elevation (eminentia arcuata) (Fig. 65), formed by the upper semicircular canal of the inner ear lying under it. The front surface is separated from the inner stony-scaly fissure (fissura petrosquamosa) (Fig. 64, 66). Between the gap and the arcuate elevation is a vast area - the tympanic roof (tegmen tympani) (Fig. 65), under which lies the tympanic cavity of the middle ear. Almost in the center of the posterior surface of the stony part (facies posterior partis petrosae), the internal auditory opening (porus acusticus internus) (Fig. 65) is noticeable, heading into the internal auditory meatus. Vessels, facial and vestibulocochlear nerves pass through it. Above and lateral to the internal auditory opening is the subarc fossa (fossa subarcuata) (Fig. 65), into which the process of the dura mater penetrates. Even more lateral to the opening is the external opening of the vestibule aqueduct (apertura externa aquaeductus vestibuli) (Fig. 65), through which the endolymphatic duct exits the cavity of the inner ear. In the center of the rough lower surface (facies inferior partis petrosae) there is an opening leading to the carotid canal (canalis caroticus), and behind it is the jugular fossa (fossa jugularis) (Fig. 66). Lateral to the jugular fossa, a long styloid process (processus styloideus) (Fig. 64, 65, 66), which is the point of origin of muscles and ligaments, protrudes downward and anteriorly. At the base of this process is the stylomastoid foramen (foramen stylomastoideum) (Fig. 66, 67), through which the facial nerve emerges from the cranial cavity. The mastoid process (processus mastoideus) (Fig. 64, 66), which is a continuation of the base of the stony part, serves as an attachment point for the sternocleidomastoid muscle.

On the medial side, the mastoid process is limited by the mastoid notch (incisura mastoidea) (Fig. 66), and along its inner, cerebral side, there is an S-shaped groove of the sigmoid sinus (sulcus sinus sigmoidei) (Fig. 65), from which to the outer surface of the skull leads mastoid opening (foramen mastoideum) (Fig. 65), relating to non-permanent venous graduates. Inside the mastoid process there are air cavities - mastoid cells (cellulae mastoideae) (Fig. 67), communicating with the middle ear cavity through the mastoid cave (antrium mastoideum) (Fig. 67).

The scaly part (pars squamosa) (Fig. 64, 65) has the shape of an oval plate, which is located almost vertically. The outer temporal surface (facies temporalis) is slightly rough and slightly convex, participates in the formation of the temporal fossa (fossa temporalis), which is the starting point of the temporal muscle. The inner cerebral surface (facies cerebralis) is concave, with traces of adjacent convolutions and arteries: digital depressions, cerebral eminences and arterial grooves. Anterior to the external auditory meatus, the zygomatic process (processus zygomaticus) rises sideways and forward (Fig. 64, 65, 66), which, connecting with the temporal process, forms the zygomatic arch (arcus zygomaticus). At the base of the process, on the outer surface of the scaly part, there is a mandibular fossa (fossa mandibularis) (Fig. 64, 66), providing a connection with the lower jaw, which is limited in front by the articular tubercle (tuberculum articularae) (Fig. 64, 66).

The tympanic part (pars tympanica) (Fig. 64) is fused with the mastoid process and the squamous part, it is a thin plate that limits the external auditory opening and the external auditory meatus in front, behind and below.

The temporal bone contains several canals:

- carotid canal (canalis caroticus) (Fig. 67), in which lies the internal carotid artery. It starts from the outer opening on the lower surface of the rocky part, goes vertically upwards, then, gently curving, passes horizontally and exits at the top of the pyramid;

- facial canal (canalis facialis) (Fig. 67), in which the facial nerve is located. It begins in the internal auditory canal, goes horizontally forward to the middle of the anterior surface of the petrous part, where, turning at a right angle to the side and passing into the posterior part of the medial wall of the tympanic cavity, it goes vertically down and opens with a stylomastoid opening;

- the muscular-tubal canal (canalis musculotubarius) (Fig. 66) is divided by a septum into two parts: the semi-canal of the muscle straining the eardrum (semicanalis m. tensoris tympani) (Fig. 67), and the semi-canal of the auditory tube (semicanalis tubae auditivae) (Fig. . 67), connecting the tympanic cavity with the pharyngeal cavity. The canal opens with an external opening lying between the anterior end of the petrous part and the scales of the occipital bone, and ends in the tympanic cavity.

The temporal bone is connected to the occipital, parietal and sphenoid bones.

The parietal bone (os parietale) (Fig. 59) is paired, flat, has a quadrangular shape and takes part in the formation of the upper and lateral parts of the cranial vault.

The outer surface (facies externa) of the parietal bone is smooth and convex. The place of its greatest convexity is called the parietal tubercle (tuber parietale) (Fig. 68). Below the tubercle are the upper temporal line (linea temporalis superior) (Fig. 68), which is the site of attachment of the temporal fascia, and the lower temporal line (linea temporalis inferior) (Fig. 68), which serves as the site of attachment of the temporal muscle.

The inner, cerebral, surface (facies interna) is concave, with a characteristic relief of the adjacent brain, the so-called digital impressions (impressiones digitatae) (Fig. 71) and tree-like branching arterial grooves (sulci arteriosi) (Fig. 69, 71).

Four edges are distinguished in the bone. The anterior frontal edge (margo frontalis) (Fig. 68, 69) is connected to the frontal bone. Rear occipital margin (margo occipitalis) (Fig. 68, 69) - with the occipital bone. The upper swept, or sagittal, edge (margo sagittalis) (Fig. 68, 69) is connected to the same edge of the other parietal bone. The lower squamous edge (margo squamosus) (Fig. 68, 69) is covered in front by the large wing of the sphenoid bone, a little further by the scales of the temporal bone, and behind it is connected to the teeth and mastoid process of the temporal bone.

Also, according to the edges, four corners are distinguished: frontal (angulus frontalis) (Fig. 68, 69), occipital (angulus occipitalis) (Fig. 68, 69), wedge-shaped (angulus sphenoidalis) (Fig. 68, 69) and mastoid (angulus mastoideus ) (Fig. 68, 69).

The frontal bone (os frontale) (Fig. 59) is unpaired, participates in the formation of the anterior part of the vault and base of the skull, eye sockets, temporal fossa and nasal cavity. Three parts are distinguished in it: the frontal scales, the orbital part and the nasal part.

Frontal scales (squama frontalis) (Fig. 70) is directed vertically and backwards. The outer surface (facies externa) is convex and smooth. From below, the frontal scales end in a pointed supraorbital margin (margo supraorbitalis) (Fig. 70, 72), in the medial part of which there is an supraorbital notch (incisura supraorbitalis) (Fig. 70), containing the vessels and nerves of the same name. The lateral section of the supraorbital margin ends with a triangular zygomatic process (processus zygomaticus) (Fig. 70, 71), which connects to the frontal process of the zygomatic bone. Behind and upward from the zygomatic process, an arcuate temporal line (linea temporalis) (Fig. 70) passes, separating the outer surface of the frontal scale from its temporal surface. The temporal surface (facies temporalis) (Fig. 70) is involved in the formation of the temporal fossa. Above the supraorbital margin on each side is the superciliary arch (arcus superciliaris) (Fig. 70), which is an arcuate elevation. Between and slightly above the superciliary arches is a flat, smooth area - the glabella (glabella) (Fig. 70). Above each arc there is a rounded elevation - frontal tubercle (tuber frontale) (Fig. 70). The inner surface (facies interna) of the frontal scales is concave, with characteristic indentations from the convolutions of the brain and arteries. The groove of the superior sagittal sinus (sulcus sinus sagittalis superioris) (Fig. 71) runs along the center of the inner surface, the edges of which in the lower section are combined into the frontal scallop (crista frontalis) (Fig. 71).

The orbital part (pars orbitalis) (Fig. 71) is steam room, takes part in the formation of the upper wall of the orbit and has the form of a horizontally located triangular plate. The lower orbital surface (facies orbitalis) (Fig. 72) is smooth and convex, facing the cavity of the orbit. At the base of the zygomatic process in its lateral section is the fossa of the lacrimal gland (fossa glandulae lacrimalis) (Fig. 72). The medial part of the orbital surface contains a trochlear fossa (fovea trochlearis) (Fig. 72), in which lies the trochlear spine (spina trochlearis) (Fig. 72). The upper cerebral surface is convex, with a characteristic relief.

The nasal part (pars nasalis) (Fig. 70) of the frontal bone in an arc surrounds the ethmoid notch (incisura ethmoidalis) (Fig. 72) and contains pits that articulate with the cells of the labyrinths of the ethmoid bone. In the anterior section there is a descending nasal spine (spina nasalis) (Fig. 70, 71, 72). In the thickness of the nasal part lies the frontal sinus (sinus frontalis), which is a paired cavity separated by a septum, belonging to the air-bearing paranasal sinuses.

The frontal bone is connected to the sphenoid, ethmoid and parietal bones.

The ethmoid bone (os ethmoidale) is unpaired, participates in the formation of the base of the skull, the orbit and the nasal cavity. It consists of two parts: a lattice, or horizontal, plate and a perpendicular, or vertical, plate.

Ethmoid plate (lamina cribosa) (Fig. 73, 74, 75) is located in the ethmoid notch of the frontal bone. On both sides of it is a lattice labyrinth (labyrinthus ethmoidalis) (Fig. 73), consisting of air-bearing lattice cells (cellulae ethmoidales) (Fig. 73, 74, 75). On the inner surface of the ethmoid labyrinth there are two curved processes: the upper (concha nasalis superior) (Fig. 74) and the middle (concha nasalis media) (Fig. 74, 75) nasal conchas.

Perpendicular plate (lamina perpendicularis) (Fig. 73, 74, 75) is involved in the formation of the septum of the nasal cavity. Its upper part ends with a cockscomb (crista galli) (Fig. 73, 75), to which a large sickle-shaped process of the dura mater is attached.