Anatomy and Physiology of Children and Adolescents - M. R. Sapin 2007

Musculoskeletal System
Skull
The Skull as a Whole (Skull Topography)

The Skull features a complex internal and external surface relief. This topography is shaped by the housing of the Brain, Sense Organs, and nerve ganglia within its osseous cavities, as well as by the presence of numerous foramina and canals for the passage of Vessels and nerves.

The upper part of the neurocranium is referred to as the cranial vault (calvaria) due to its shape. The calvaria 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. Sutures are visible on the external surface of the cranial vault: the sagittal suture between the parietal bones, the coronal suture between the frontal and parietal bones, the lambdoid suture between the parietal bones and the occipital squama, and the squamous suture between the squamous part of the Temporal bone and the Parietal bone. The frontal eminences are visible in the anterior region of the vault, the supraorbital margins and arches run above the orbits, and a small area, the glabella, lies between them. The parietal eminences, along with the superior and inferior temporal lines, stand out on the upper-lateral surfaces of the vault.

When viewed laterally, the skull reveals the frontal, parietal, temporal, occipital, and sphenoid bones. Also visible are the zygomatic arch (formed by the temporal process of the Zygomatic bone and the zygomatic process of the temporal bone), the external acoustic meatus, the mastoid process, the Maxilla and Mandible, and the temporal, infratemporal, and pterygopalatine fossae.

The temporal fossa is bounded superiorly and posteriorly by the temporal line and anteriorly by the zygomatic bone; inferiorly, it continues into the infratemporal fossa. The superior wall of the infratemporal fossa is formed by the greater wing of the sphenoid bone and a portion of the squamous temporal bone; the anterior wall by the infratemporal surface of the maxilla and the zygomatic bone; the medial wall by the lateral plate of the pterygoid process of the sphenoid bone; and the lateral wall by the zygomatic arch and the ramus of the mandible.

The pterygopalatine fossa lies between the Base of the pterygoid process of the sphenoid bone posteriorly and the maxillary tuberosity anteriorly. Its medial wall is formed by the perpendicular plate of the Palatine bone (or the medial plate of the pterygoid process of the sphenoid bone). The pterygopalatine fossa communicates with the Nasal cavity via the sphenopalatine foramen, with the middle cranial fossa via the foramen rotundum, with the Orbit via the inferior orbital fissure, with the region of the lacerum foramen via the pterygoid canal, and with the Oral Cavity via the greater palatine canal.

The external cranial base is formed by the Inferior surface of the neurocranium and part of the viscerocranium (Fig. 23). The anterior division of the base is formed by the hard palate and the alveolar arch constituted by the maxillary bones. The middle division, formed by the temporal and sphenoid bones, lies between the posterior margin of the hard palate anteriorly and the anterior margin of the foramen magnum posteriorly. On the inferior surface of the pyramid of each temporal bone, the external opening of the carotid canal, the jugular fossa, the styloid process, and the stylomastoid foramen (the exit of the facial canal) are visible. The mandibular fossa and articular tubercle are located at the base of the zygomatic process of the temporal bone, while the lacerum foramen is situated at the apex of the pyramid. The spinous and ovale foramina are visible on the greater wing of the sphenoid bone. In the center of the posterior division of the skull lies the foramen magnum, flanked by the occipital condyles. Inferior to each condyle is the external opening of the hypoglossal canal. Lateral to the condyle is the jugular foramen, and further lateral and posterior are the condylar fossa and the mastoid process.

The relief of the internal cranial base (Fig. 24) corresponds to the inferior surface of the brain. Three cranial fossae are distinguished on the internal cranial base: anterior, middle, and posterior.

The anterior cranial fossa, which accommodates the frontal lobes of the cerebral hemispheres, is formed by the orbital parts of the frontal bone, the cribriform plate of the Ethmoid bone, and the body and lesser wings of the sphenoid bone. The posterior margin of the lesser wings separates the anterior cranial fossa from the middle cranial fossa, which houses the temporal lobes of the brain. The hypophysial fossa of the sella turcica contains the Pituitary Gland.

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Fig. 23. External cranial base:

1 — palatine process of maxilla; 2 — incisive foramen; 3 — median palatine suture; 4 — transverse palatine suture; 5 — choanae; 6 — inferior orbital fissure; 7 — zygomatic arch; 8 — wing of Vomer; 9 — pterygoid fossa; 10 — lateral plate of pterygoid process; 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 aperture; 28 — stylomastoid foramen; 29 — lacerum foramen; 30 — petrotympanic fissure; 31 — foramen spinosum; 32 — articular tubercle; 33 — sphenosquamosal suture; 34 — pterygoid hamulus; 35 — greater palatine foramen; 36 — zygomaticomaxillary suture

Fig. 24. Internal cranial base:

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

The middle cranial fossa is formed by the body and greater wings of the sphenoid bone, the anterior surface of the petrous pyramids, and the squamous parts of the temporal bones. On the lateral surface of the body of the sphenoid bone, the carotid sulcus is visible on each side. The lacerum foramen is located near the apex of the pyramid. The superior orbital fissure is situated on each side between the lesser and greater wings and the body of the sphenoid bone. Posterior and inferior to this fissure lie the foramen rotundum, foramen ovale, and foramen spinosum. The trigeminal impression is visible on the anterior surface of the petrous pyramid of the temporal bone near its apex.

The posterior cranial fossa, which houses the Cerebellum, is separated from the middle fossa by the superior borders of the petrous pyramids of the temporal bones. The posterior cranial fossa is formed by the Occipital bone and the posterior surface of the petrous pyramids. The foramen magnum is located in the center of the fossa. Anterior to the foramen lies the clivus, a sloping bony area that Supports the Pons and the Medulla Oblongata. The openings of the hypoglossal canal and the jugular foramen are located on either side of the foramen magnum. The internal acoustic opening is situated on the posterior surface of the pyramid.

Anterior inspection of the skull reveals the high forehead, mandible, maxillae, and other bones, as well as the orbits, the piriform aperture (of the Nose), and the oral cavity.

The orbit is a paired cavity that houses the visual organ. In shape, it resembles a quadrangular pyramid whose apex is directed posteriorly and medially, while its base faces anteriorly. The orbit has four walls. The superior wall is formed by the orbital part of the frontal bone and the lesser wing of the sphenoid bone. The inferior wall is constituted by the orbital surface of the body of the maxilla and the zygomatic bone; the lateral wall by the greater wing of the sphenoid bone and the zygomatic bone; and the medial wall by the orbital plate of the ethmoid bone and the Lacrimal bone. In the anterior part of the medial wall lies the fossa for the lacrimal sac, which continues into the nasolacrimal canal leading into the nasal cavity. The superior orbital fissure and the optic canal connect the orbit to the middle cranial fossa. The inferior orbital fissure leads into the pterygopalatine fossa.

The nasal cavity serves as the initial segment of the respiratory tract and contains the Organ of Smell. It features an anterior entrance (the piriform aperture) and two posterior exits (the choanae) leading into the Pharynx. The bony nasal septum, formed by the perpendicular plate of the ethmoid bone and the vomer, divides the nasal cavity into left and right halves. The lateral wall is formed by the maxilla, the ethmoidal labyrinth, the lacrimal bone, and the medial plate of the pterygoid process of the sphenoid bone.

Three nasal conchae are visible on the lateral wall. The Inferior nasal concha is an independent bone. The middle and superior nasal conchae are formed by processes of the ethmoidal labyrinth. The nasal conchae divide the lateral nasal region into three nasal meatuses: inferior, middle, and superior. The inferior nasal meatus lies between the inferior wall of the nasal cavity and the inferior concha; the nasolacrimal canal opens into it. The middle nasal meatus is located between the inferior and middle conchae; the anterior and middle ethmoidal Cells, along with the openings (apertures) of the frontal and maxillary sinuses, open into it. The superior nasal meatus, situated between the middle and superior nasal conchae, receives the openings of the posterior ethmoidal cells and the aperture of the sphenoid sinus.

The superior wall of the nasal cavity is formed by the nasal bones, the nasal part of the frontal bone, the cribriform plate of the ethmoid bone, and the body of the sphenoid bone. The inferior wall of the nasal cavity is constituted by the superior surface of the hard palate.

The oral cavity is bounded anteriorly and laterally by the Teeth, alveolar processes of the maxillae, alveolar arch, and the body of the mandible, and superiorly by the hard palate.