MEDICAL BIOLOGY, HUMAN ANATOMY, PHYSIOLOGY AND PATHOLOGY - Y.I. Fedonyuk 2010

ANATOMY, PHYSIOLOGY, PATHOLOGY

SECTION 2. THE LOCOMOTOR SYSTEM (THE MECHANISM OF MOVEMENT)

SKELETON OF THE HEAD. THE SKULL

4. THE SKULL AS A WHOLE

As noted above, the Skull is divided into the neurocranium (braincase) and the viscerocranium (facial Skeleton). The internal surface of the BONES OF THE neurocranium is known as the endocranial surface. It features elevations and depressions that reflect the relief of the Brain. Also clearly visible here are sulci formed by the imprints of the venous sinuses (Dural Venous Sinuses) of the dura mater, as well as arterial sulci, which are traces left by adjacent Arteries.

The skull is traditionally divided into its upper part, the calvaria (skull roof), and its lower part, the base (skull base).

The calvaria is formed by the parietal bones, the squama of the frontal, occipital, and temporal bones, and a portion of the greater wings of the Sphenoid bone.

The bones of the calvaria consist of two compact plates enclosing a layer of spongy bone known as the diploë (Fig. 2.24), situated between the external and internal plates. The internal plate is also called the vitreous (glassy) plate because, upon cranial trauma, it fractures more easily than the external plate. The skull base (basis cranii) features internal and external surfaces. On the internal surface, the anterior, middle, and posterior cranial fossae are distinguished. These fossae contain various foramina and canals through which Blood Vessels and nerves pass (Fig. 2.25).

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Fig. 2.24. Bone of the cranial vault: 1 - external plate; 2 - diploë; 3 - internal plate.

Fig. 2.25. Internal Base of the skull

The anterior cranial fossa is separated from the middle cranial fossa by the posterior margin of the lesser wings and the tuberculum sellae of the sphenoid bone; the middle cranial fossa is separated from the posterior fossa by the superior border of the petrous part of the Temporal bone and the dorsum sellae of the sphenoid bone.

The anterior cranial fossa contains the following anatomical structures: the foramen cecum, crista galli, and cribriform plate.

The middle cranial fossa contains the optic canal, superior orbital fissure, prechiasmatic and carotid sulci, sella turcica, hypophyseal fossa, as well as the foramen rotundum, foramen ovale, foramen spinosum, and lacerum foramen.

The posterior cranial fossa contains the foramen magnum, clivus, jugular and internal acoustic openings, facial and hypoglossal canals, internal occipital protuberance, sulci for the superior and inferior petrosal sinuses, as well as sulci for the superior sagittal, sigmoid, and transverse sinuses.

The external base of the skull features the following main anatomical structures: the alveolar arch, bony palate; foramina—incisive, greater and lesser palatine, lacerum, ovale, spinosum, jugular, stylomastoid, and foramen magnum; canals—incisive, greater and lesser palatine, pterygoid, carotid, and hypoglossal; processes—pterygoid, styloid, and mastoid; fossae—mandibular, jugular, and condylar; Vomer, choanae, external occipital protuberance, occipital condyle, pharyngeal tubercle, mastoid notch, and the sulcus for the occipital artery.

In the region of the facial skull, there are A number of anatomical structures that house important Organs. On its anterior surface are the Orbit, Nasal cavity, and Oral Cavity; on the lateral surface are the infratemporal and pterygopalatine fossae (Fig. 2.26).

Fig. 2.26. External base of the skull

When viewed from the front, the orbits are visible, with the nasal cavity aperture located between them.

The orbit serves as a receptacle for the Eyeball, its accessory structures, and the lacrimal gland. It has four walls—superior, inferior, lateral, and medial—which are formed by the cranial bones. It features the superior orbital fissure and the optic canal, which open into the middle cranial fossa. The inferior orbital fissure leads into the pterygopalatine fossa, and the nasolacrimal canal leads into the inferior nasal meatus (Fig. 2.27).

Fig. 2.27. The orbit; anterior view

The nasal cavity (cavum nasi) occupies a central position in the facial skeleton, serves as the initial segment of the respiratory tract, and contains the Organ of Smell. It features an entrance aperture and two exits (choanae). The bony septum consists of the vomer and the perpendicular plate of the Ethmoid bone, dividing the nasal cavity into two halves (Fig. 2.28). The superior, inferior, medial, and lateral walls of the nasal cavity are distinguished. The medial wall is formed by the nasal septum. The superior, middle, and inferior nasal conchae are located on the lateral wall. Below each concha, the superior, middle, inferior, and common nasal meatuses are formed.

Fig. 2.28. Sagittal section of the facial skeleton. Bony septum of the nasal cavity; left view

The superior nasal meatus lies between the superior and middle nasal conchae (beneath the superior nasal concha). It communicates with the pterygopalatine fossa (via the sphenopalatine foramen), the anterior cranial fossa (via the cribriform plate), the sphenoid and ethmoid sinuses (specifically, the posterior ethmoidal Cells), and the orbit (via the posterior ethmoidal foramen).

The middle nasal meatus is situated between the inferior and middle nasal conchae (beneath the middle nasal concha). The maxillary (sinus of Highmore) and frontal sinuses, as well as the middle and anterior ethmoidal cells, open into it.

The inferior nasal meatus is bounded by the hard palate and the Inferior nasal concha (located beneath the inferior nasal concha). It communicates with the orbit through the nasolacrimal canal. The common nasal meatus is a narrow sagittal cleft-like space situated between the conchae and the bony nasal septum. It communicates with the oral cavity via the incisive canal (Fig. 2.29).

Fig. 2.29. Sagittal section of the facial skeleton.

The oral cavity (cavum oris) features a superior bony wall (hard palate), as well as anterior and lateral walls (alveolar processes of the jaws and Teeth).

On the lateral surface of the skull, paired fossae are distinguished: the temporal, infratemporal, and pterygopalatine fossae. The boundary between the temporal and infratemporal fossae is formed by the zygomatic arch (laterally) and the infratemporal crest (medially).

The infratemporal fossa continues into the pterygopalatine fossa. The latter communicates with the cranial cavity, the orbit, and the nasal and oral cavities (Fig. 2.30).

Fig. 2.30. Pterygopalatine fossa