Human Anatomy - Kotsan I. Ya. 2009

Skeleton of the Head
The Skull as a Whole

When examining The Skull as a whole, it is studied from various Perspectives. The superior view of the skull is designated as the vertical aspect (norma verticalis), the inferior view as the basal aspect (norma basilaris), the anterior view as the facial aspect (norma facialis), the posterior view as the occipital aspect (norma occipitalis), and the lateral view as the lateral aspect (norma lateralis).

Upon inspecting the skull from above, the cranial vault is visible; from below, the cranial base; from the front, the facial Skeleton; from behind, the posterior part of the neurocranium; and laterally, a series of depressions (fossae) bounded by various bones.

To individually characterize the shape and dimensions of The Skull and perform measurements, the following topographical landmarks are used: basion — the midpoint of the anterior margin of the foramen magnum; opisthion — the midpoint of the posterior margin of the foramen magnum; bregma — the junction of the coronal and sagittal sutures; vertex — the highest point of the cranial vault; nasion — the midpoint of the suture between the frontal and nasal bones; inion — the center of the external occipital protuberance; lambda — the junction of the lambdoid and sagittal sutures; asterion — the junction of the occipital, parietal, and temporal bones; pterion — the junction of the frontal, parietal, temporal, and sphenoid bones.

The upper part of the neurocranium is referred to as the vault (calvaria) due to its shape. The lower part serves as the base (basis). The boundary between the base and the vault runs along an imaginary line passing through the following Anatomical Features: 1) the external occipital protuberance, 2) the superior nuchal line; 3) the Base of the mastoid process; 4) the upper margin of the external acoustic meatus; 5) the ROOT of the zygomatic process of the Temporal bone; 6) the infratemporal crest of the greater wing of the Sphenoid bone, 7) the sphenozygomatic suture, 8) the zygomatic process of the Frontal bone, 9) the supraorbital margin, 10) the nasal margin of the frontal bone.

The cranial vault is formed by the squamous part of the frontal bone, the parietal bones, the squamous PARTS OF THE occipital and temporal bones, and the lateral parts of the greater wings of the sphenoid bone.

On the external surface of the cranial vault, sutures (sagittal, coronal, lambdoid, squamous) are visible between the bones. In the anterior region of the external surface, the frontal eminences protrude; below them, above the orbits, are the superciliary arches, and above the root of the Nose, a small flat area called the glabella is discernible. In the anterolateral Regions of the external surface, the parietal eminences project. Below each eminence, the arch-shaped superior temporal line runs. The anterolateral region of the vault, bounded above by the inferior temporal line and below by the infratemporal crest of the greater wing of the sphenoid bone, is called the temporal fossa. Below the temporal fossa lies the infratemporal fossa, which is separated from the temporal one by the infratemporal crest.

On the internal surface of the cranial vault, sutures similar to those on its external surface are visible; digital impressions (impressiones digitatae), which are imprints of the cerebral gyri; and arterial and venous sulci, which are traces left by the apposition of Arteries and Veins. Near the sagittal suture, granular pits (foveolae granulares) are noticeable, formed by the projections of the arachnoid granulation of the Brain.

The cranial base, just like the vault, is viewed from two perspectives: externally (inferiorly) as the external cranial base, and internally as the internal cranial base.

The external cranial base (basis cranii externa) is formed by the Inferior surface of the neurocranium and part of the viscerocranium (Fig. 45). It is conventionally divided into anterior and posterior regions. The anterior region is formed by the palatine and alveolar processes of the maxillae, as well as the horizontal plates of the palatine bones. The posterior region of the external cranial base consists of a part of the body and the greater wings of the sphenoid bone, as well as the temporal and occipital bones.

The relief of the external cranial base is quite complex. In its anterior part lies the bony palate (palatum osseum), along the midline of which runs the suture and where the incisive canal (canalis incisivus) begins. In the posterior region of the bony palate, There is a transverse suture along with the greater and lesser palatine foramina, which continue into the canals of the same name.

In the posterior part of the external cranial base (almost in the center) is the foramen magnum, flanked by the occipital condyles. Posterior to each condyle lies the condylar fossa with an inconstant opening — the condylar canal. The base of each condyle is pierced by the hypoglossal canal. The posterior region of the cranial base terminates in the external occipital protuberance and the superior and inferior nuchal lines extending laterally to the right and left from the occipital protuberance. Anterior to the foramen magnum lies the basilar part of the Occipital bone with a well-defined pharyngeal tubercle. Flanking the occipital bone is the inferior surface of the petrous part of the temporal bone, which features the following structures: the external opening of the carotid canal; the entrance to the musculotubular canal; the jugular fossa and jugular notch, which together with the jugular notch of the occipital bone form the jugular foramen (foramen jugulare); the styloid process; the mastoid process; and between them, the stylomastoid foramen. Laterally adjacent to the petrous part of the temporal bone is the tympanic part of the temporal bone, which bounds the external acoustic meatus. Posteriorly, the tympanic part of the temporal bone joins the mastoid process via the tympanomastoid fissure. On the posteromedial side of the mastoid process are the mastoid notch and the occipital artery sulcus. On the horizontally situated area of the squamous part of the temporal bone lies the mandibular fossa, which serves for articulation with the condylar process of the Mandible. Anterior to this fossa is the articular tubercle. Between the petrous and squamous parts of the temporal bone enters the posterior part of the greater wing of the sphenoid bone; here, the spinous and oval foramina are clearly visible.

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Fig. 45. External cranial base (after M. R. Sapin)

1 — palatine process of Maxilla, 2 — incisive foramen, 3 — median palatine suture, 4 — transverse palatine suture, 5 — choana, 6 — inferior orbital fissure, 7 — zygomatic arch, 8 — wing of Vomer, 9 — sphenoidal process of Palatine bone, 10 — pterygoid fossa, 11 — pterygoid process, 12 — foramen ovale, 13 — mandibular fossa, 14 — styloid process, 15 — external acoustic meatus, 16 — mastoid process, 17 — mastoid notch, 18 — occipital condyle, 19 — condylar fossa, 20 — foramen magnum, 21 — inferior nuchal line, 22 — external occipital protuberance, 23 — pharyngeal tubercle, 24 — condylar canal, 25 — jugular foramen, 26 — occipitomastoid suture, 27 — external carotid opening, 28 — stylomastoid foramen, 29 — foramen lacerum, 30 — petrotympanic fissure, 31 — foramen spinosum, 32 — articular tubercle, 33 — sphenosquamosal suture, 34 — pterygoid hamulus, 35 — greater palatine foramen, 36 — zygomaticomaxillary suture

The petrous part of the temporal bone is separated from the occipital bone by the petro-occipital fissure (fissura petrooccipitalis), and from the greater wing of the sphenoid bone by the sphenopetrosal fissure (fissura sphenopetrosa). In addition, on the inferior surface of the external cranial base, the foramen lacerum is visible, located between the apex of the petrous part of the temporal bone and the sphenoid bone. Between the palatine bone and the vaginal process of the sphenoid bone lies the palatovaginal canal (canalis palatovaginalis); between the vomer and the vaginal process of the sphenoid bone is the vomerovaginal canal (canalis vomerovaginalis); and between the vomer and the rostrum of the sphenoid bone runs the vomerorostral canal (canalis vomerorostralis).

The internal cranial base (basis cranii interna) has a concave, uneven surface. It is divided into three cranial fossae: anterior, middle, and posterior (Fig. 46).

Fig. 46. Internal cranial base (after M. R. Sapin)

1 — orbital part of frontal bone, 2 — crista galli, 3 — cribriform plate, 4 — optic canal, 5 — hypophysial fossa, 6 — dorsum sellae, 7 — foramen rotundum, 8 — foramen ovale, 9 — foramen lacerum, 10 — foramen spinosum, 11 — internal acoustic meatus, 12 — jugular foramen, 13 — hypoglossal canal, 14 — lambdoid suture, 15 — clivus, 16 — transverse sinus sulcus, 17 — internal occipital protuberance, 18 — foramen magnum, 19 — occipital squama, 20 — sigmoid sinus sulcus, 21 — petrous part (pyramid) of temporal bone, 22 — squamous part of temporal bone, 23 — greater wing of sphenoid bone, 24 — lesser wing of sphenoid bone

The anterior cranial fossa (fossa cranii anterior) is formed by the orbital parts of the frontal bones, the lesser wings of the sphenoid bone, and the cribriform plate of the Ethmoid bone. The frontal lobes of the cerebral hemispheres lie within the anterior cranial fossa. In the center of the anterior cranial fossa (in the middle of the cribriform plate) is the crista galli. Anterior to it are the foramen cecum and the frontal crest. The anterior cranial fossa communicates with the Nasal cavity through the foramina in the cribriform plate. Through these foramina, the olfactory nerves pass from the nasal cavity into the cranial cavity.

The middle cranial fossa (fossa cranii media) is considerably deeper than the anterior one. It is formed by the body and greater wings of the sphenoid bone, the anterior surfaces of the petrous parts, and the squamous parts of the temporal bones. The temporal lobes of the cerebral hemispheres are lodged in the middle cranial fossa. The fossa is subdivided into three parts: two lateral and one central. The central part is occupied by the sella turcica. At the floor of the sella turcica lies the hypophysial fossa, which lodges the Pituitary Gland (hypophysis). Anterior to the fossa runs the prechiasmatic sulcus, which leads into the right and left optic canals. On the lateral surface of the body of the sphenoid bone lies a well-marked carotid sulcus, and near the apex of the petrous part, the foramen lacerum is visible. Also located here, between the lesser wing, the greater wing, and the body of the sphenoid bone, is the superior orbital fissure, through which pass the anterior meningeal artery, the superior ophthalmic vein, the oculomotor, trochlear, and abducens nerves, and the first branch of the Trigeminal nerve — the ophthalmic nerve. Posterior to the superior orbital fissure is the foramen rotundum, which serves for the passage of the maxillary nerve (the second branch of the trigeminal nerve), followed by the foramen ovale for the mandibular nerve (the third branch of the trigeminal nerve). Near the posterior margin of the greater wing is the foramen spinosum for The entry of the middle meningeal artery into the cranial cavity. On the anterior surface of the petrous part of the temporal bone, within a relatively small area, are located the trigeminal impression, the hiatus for the greater petrosal nerve, the sulcus for the greater petrosal nerve, the hiatus for the lesser petrosal nerve, the sulcus for the lesser petrosal nerve, the tegmen tympani, and the arcuate eminence.

The posterior cranial fossa (fossa cranii posterior) is the deepest. It is formed by the part of the occipital bone situated below the transverse sinus sulcus, the posterior surface of the petrous parts and the internal surface of the mastoid processes of the temporal bones, the posterior part of the body of the sphenoid bone, and the posteroinferior angles of the parietal bones. In the center of the posterior fossa, the foramen magnum is visible, anterior to which lies the clivus that Supports the Pons and the Medulla Oblongata. Flanking the foramen magnum are the openings of the hypoglossal canals, transmitting the hypoglossal nerves (XII cranial pair), and the jugular foramina, through which pass the glossopharyngeal (IX pair), vagus (X pair), and accessory (XI pair) nerves. In addition to nerves, the internal jugular veins exit the cranial cavity through the jugular foramina. On the posterior surface of the petrous part of the temporal bone is the internal acoustic meatus, through which the Vestibulocochlear nerve passes.

Upon inspecting the facial skeleton from the front (facial aspect), A number of structures that serve as receptacles for Organs immediately draw attention. These are the orbits, the nasal cavity, and the Oral Cavity.

The Orbit (orbita) has the shape of an irregular four-sided pyramid (Fig. 47). The base of the pyramid faces forward and forms the orbital opening, which is bounded by the supraorbital and infraorbital margins. The apex of the pyramid is directed backward and medially; the optic canal runs through it. The orbit contains: the Eyeball with its Muscles and orbital fascia, the Optic nerve, the lacrimal gland, Blood Vessels, nerves, and adipose tissue.

The orbital cavity is bounded by four walls: superior, medial, inferior, and lateral.

The superior wall (paries superior) is formed by the orbital part of the frontal bone and the lesser wing of the sphenoid bone. At the border between the superior and lateral walls lies the shallow fossa for the lacrimal gland. Near the medial margin of the superior wall is a barely noticeable depression, the trochlear fossa.

Fig. 47. The orbit (anterior view)

1 — optic canal, 2 — posterior lacrimal crest, 3 — lacrimal sac fossa, 4 — anterior lacrimal crest, 5 — infraorbital groove, 6 — inferior orbital fissure, 7 — orbital process of the palatine bone, 8 — superior orbital fissure

The medial wall (paries medialis) is formed by the frontal process of the maxilla, the Lacrimal bone, the orbital plate of the ethmoid bone, and the body of the sphenoid bone. In the anterior section of the medial wall lies the lacrimal sac fossa, which extends inferiorly into the nasolacrimal canal that opens into the inferior nasal meatus of the nasal cavity. Slightly posterior and superior to the lacrimal sac fossa in the upper part of the medial wall, within the suture between the frontal bone and the orbital plate of the ethmoid bone, the anterior and posterior ethmoidal foramina are visible for the corresponding nerves and vessels.

The inferior wall (paries inferior) of the orbit is formed by the orbital surfaces of the maxilla and Zygomatic bone, supplemented posteriorly by the orbital process of the palatine bone. The inferior wall of the orbit contains the infraorbital groove, which anteriorly continues into the infraorbital canal of the same name.

The lateral wall (paries lateralis) is formed by the orbital surface of the zygomatic bone and the orbital surface of the greater wing of the sphenoid bone. Between the lateral and superior walls deep within the orbit lies the superior orbital fissure, which connects the orbit to the middle cranial fossa. Between the lateral and inferior walls of the orbit is the inferior orbital fissure, which connects the orbit to the pterygopalatine and infratemporal fossae.

The nasal cavity (cavitas nasi) serves as the bony foundation for the initial sections of the Respiratory system and the Olfactory Organ. The entrance to the nasal cavity is represented by the piriform aperture (apertura piriformis), which is bounded by the nasal notches of the maxillae and the inferior margins of the nasal bones. The posterior openings of the nasal cavity—the choanae—connect the nasal cavity to the pharyngeal cavity. By means of the bony nasal septum (septum nasi osseum), formed by the perpendicular plate of the ethmoid bone and the vomer, the nasal cavity is divided into right and left halves, each of which has 4 walls: superior, inferior, medial, and lateral.

The superior wall (paries superior) of the nasal cavity is formed by the Nasal bone, the cribriform plate of the ethmoid bone, and the body of the sphenoid bone.

The inferior wall (paries inferior) of the nasal cavity consists of the palatine process of the maxilla and the horizontal plate of the palatine bone.

The medial wall (paries medialis) of each half of the nasal cavity is the bony nasal septum.

The lateral wall (paries lateralis) of the nasal cavity has the most complex Structure. It is formed by the body and frontal process of the maxilla, the lacrimal bone, the ethmoidal labyrinth, the perpendicular plate of the palatine bone, and the medial plate of the pterygoid process of the sphenoid bone. Three nasal conchae hang down from the lateral wall into the nasal cavity: the superior, middle, and inferior nasal conchae, which divide the lateral part of the nasal cavity into three nasal meatuses: superior, middle, and inferior.

The superior nasal meatus (meatus nasalis superior) is located between the superior and middle nasal conchae. The posterior ethmoidal Cells open into it. Above the posterior part of the superior nasal concha lies the sphenoethmoidal recess (recessus sphenoethmoidalis), into which the aperture of the sphenoidal sinus opens.

The middle nasal meatus (meatus nasalis medius) is located between the middle and inferior nasal conchae. The anterior and middle ethmoidal cells open into it, as well as the apertures of the frontal and maxillary sinuses, while the sphenopalatine foramen (foramen sphenopalatinum), located posterior to the middle nasal concha, connects the middle nasal meatus with the pterygopalatine fossa.

The inferior nasal meatus (meatus nasalis inferior) is located between the Inferior nasal concha and the inferior wall of the nasal cavity. The nasolacrimal, incisive, greater and lesser palatine canals open into the inferior nasal meatus.

The oral cavity (cavitas oris) is bounded anteriorly and laterally by the upper and lower alveolar arches along with the Teeth, as well as the body and rami of the mandible, and superiorly by the hard (bony) palate. The bony palate (palatum osseum) is formed by the palatine processes of the maxillae and the horizontal plates of the palatine bones. The inferior surface of the bony palate is concave, with the median palatine suture running along its midline; near the anterior end of this suture lies the incisive foramen, which leads into the incisive canal. The canal opens on the upper (nasal) surface of the hard palate by two openings, each located on either side of the nasal crest. Posterior to the terminal parts of the transverse palatine suture, at the base of each horizontal plate, are the opening of the greater palatine canal and 2–3 lesser palatine foramina, which connect the oral cavity to the pterygopalatine fossa.

When examining the skull from the sides (lateral norma), the following fossae are visible on the skull surface: the temporal, infratemporal, and pterygopalatine fossae (Fig. 48).

The temporal fossa (fossa temporalis) is a flat depression that houses the temporalis Muscle. The temporal surface of the greater wings of the sphenoid bone, the squamous part of the temporal bone, and partially the parietal and frontal bones take part in The formation of the temporal fossa. The fossa communicates with the orbital cavity via the inferior orbital fissure, and with the pterygopalatine fossa via the pterygomaxillary fissure.

Fig. 48. Temporal, infratemporal, and pterygopalatine fossae (after R. D. Sinelnikov)

1 — greater wing, 2 — sphenosquamosal suture, 3 — sphenozygomatic suture, 4 — inferior orbital fissure, 5 — sphenopalatine foramen, 6 — alveolar foramina, 7 — pterygoid hamulus, 8 — pyramidal process of the palatine bone, 9 — pterygoid process, 10 — pterygopalatine fossa, 11 — infratemporal fossa, 12 — infratemporal crest, 13 — squamous part of the temporal bone

The infratemporal fossa (fossa infratemporalis) is formed by the greater wing of the sphenoid bone, the lateral plate of the pterygoid process of the sphenoid bone, the infratemporal surface of the maxilla, the zygomatic bone, and the ramus of the mandible. The fossa is filled with the pterygoid muscles, vessels, nerves, and adipose tissue.

The pterygopalatine fossa (fossa pterygopalatina) is the smallest of all the external cranial fossae. It has three walls: anterior, posterior, and medial. The anterior wall of the fossa is formed by the maxillary tuberosity, the posterior by the base of the pterygoid process of the sphenoid bone, and the medial by the perpendicular plate of the palatine bone. The pterygopalatine fossa gradually narrows inferiorly and continues into the greater palatine canal, which superiorly has the same walls as the fossa, while inferiorly it is bounded by the maxilla and the palatine bone. Five openings open into the pterygopalatine fossa. Through the sphenopalatine foramen it communicates with the nasal cavity, through the foramen rotundum with the middle cranial fossa, through the inferior orbital fissure with the orbital cavity, through the pterygopalatine canal with the region of the lacerum foramen (on the external surface of the cranial base), and through the greater palatine canal with the oral cavity.