Human Anatomy - H. I. Koliadenko 2009

Musculoskeletal System
Skeleton of the Skull
The Skull as a Whole

Skull topography. As previously noted, the skull is divided into the neurocranium (braincase) and the viscerocranium (facial Skeleton). The neurocranium, in turn, is subdivided into the cranial vault (calvaria) and the cranial base. Both the vault and the base are formed by individual bones connected by sutures. The cranial base has a more complex Structure than the vault. On the internal surface of the cranial base, three cranial fossae are distinguished: the anterior, middle, and posterior cranial fossae (Fig. 59).

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 crista galli lies in the center of the anterior fossa. Olfactory nerve fibers pass through the cribriform plate into the Nasal cavity. The frontal lobes of the cerebrum rest within the anterior cranial fossa.

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Fig. 59. Internal Base of the skull:

1 — frontal sinus; 2 — cribriform plate of the ethmoid bone; 3 — anterior cranial fossa; 4 — sella turcica; 5 — middle cranial fossa; 6 — acoustic opening; 7 — posterior cranial fossa; 8 — foramen magnum; 9 — petrous part of the Temporal bone; 10 — foramen ovale; 11 — foramen rotundum; 12 — superior orbital fissure; 13 — hypoglossal canal; 14 — jugular foramen

The middle cranial fossa is formed by the body and greater wings of the sphenoid bone, the anterior surface of the petrous part, and partly the squamous part of the temporal bone. The lesser wings of the sphenoid bone serve as the boundary between the anterior and middle cranial fossae. The superior margin of the petrous part of the temporal bone and the dorsum sellae separate the middle fossa from the posterior one. The elevation in the center of the middle fossa is formed by the body of the sphenoid bone with the sella turcica and the hypophysial fossa (pituitary fossa). Grooves for the Internal Carotid Artery run along the lateral surfaces of the body near the sella turcica. The lateral PARTS OF THE middle cranial fossa are deeper and accommodate the temporal lobes of the Brain. The following openings are localized in the middle fossa: the optic canals at the base of the lesser wings; and the superior orbital fissure located between the lesser and greater wings of the sphenoid bone. The optic canals and orbital fissures connect the middle cranial fossa with the orbits. Passing through the canal and orbital fissures are the optic nerves, ophthalmic Arteries, the superior branch of the Trigeminal nerve, as well as the trochlear and abducens nerves, which innervate and supply Blood to the Eyeball. At the base of the greater wings are the foramen rotundum, foramen ovale, and foramen spinosum, through which blood Vessels and nerves pass. Via the foramen rotundum, the middle cranial fossa communicates with the pterygopalatine fossa, and via the foramen ovale — with the external surface of the skull, between the apex of the petrous part of the temporal bone and the sphenoid bone.

The posterior cranial fossa is formed by the Occipital bone, the posterior surfaces of the petrous parts of the temporal bones, and the mastoid parts of the temporal bone. In the center of the occipital bone lies the foramen magnum, through which the brain connects with the Spinal Cord. On the sides of the foramen are the hypoglossal canals and jugular foramina. The clivus is located between the dorsum sellae and the foramen magnum. On the posterior surface of the petrous part is the internal acoustic meatus.

On the external surface of the skull (Figs. 60, 61), temporal, infratemporal, and pterygopalatine fossae are located laterally.

The temporal fossa occupies the lateral surface of the skull. It is formed by the Inferior surface of the Parietal bone, the squamous part of the temporal bone, and the greater wings of the sphenoid bone. Externally, the temporal fossa is bounded by the zygomatic arch.

The infratemporal fossa is separated from the temporal fossa by the infratemporal crest, which is located on the external surface of the greater wing of the sphenoid bone. It is formed by the inferior surface of the greater wing of the sphenoid bone, the lateral plate of the pterygoid process, and the infratemporal surface of the Maxilla. It is bounded by the ramus of the Mandible. Through the foramen ovale and foramen spinosum, the infratemporal fossa communicates with the middle cranial fossa.

The pterygopalatine fossa is formed by the perpendicular plate of the Palatine bone, the pterygoid process of the sphenoid bone, and the maxillary tuberosity. The inferior orbital fissure, the pterygopalatine canal, and the pterygoid canal open into the pterygopalatine fossa.

Fig. 60. Skull, anterior view:

1 — squamous part of the frontal bone; 2 — frontal tuber; 3 — supraorbital margin (superciliary arch); 4 — supraorbital margin; 5 — zygomatic process; 6 — Nasal bone; 7 — Zygomatic bone; 8 — zygomatic process; 9 — body of the maxilla; 10 — angle of the mandible; 11 — alveolar process of the mandible; 12 — mental protuberance; 13 — body of the mandible; 14 — mental foramen; 15 — alveolar process; 16 — ramus of the mandible; 17 — frontonasal process; 18 — temporal process; 19 — frontal process; 20 — glabella; 21 — temporal line

On the anterior surface of the facial skull, There are two orbits and the nasal cavity. The Orbit (orbitae) resembles a quadrangular pyramid in shape, with its apex directed posteriorly and its base anteriorly. Its superior margin is bounded by the frontal bone, the medial margin by the nasal part of the frontal bone and the frontal process of the maxilla, and the inferior margin by the bodies of the maxilla and zygomatic bone; the lateral wall of the orbit is formed by the greater wing of the sphenoid bone, part of the zygomatic bone, and the zygomatic process of the frontal bone. The medial wall is formed by part of the frontal process of the maxilla, the Lacrimal bone, the perpendicular plate of the ethmoid bone, and part of the lateral surface of the body of the sphenoid bone. Located near the apex of the orbit is the optic canal, and superiorly and laterally lies the superior orbital fissure, which connect the orbit to the middle cranial fossa. Between the greater wing and the maxilla is the inferior orbital fissure, connecting the orbit with the infratemporal and pterygopalatine fossae. The nasolacrimal canal runs along the medial surface, leading into the inferior nasal meatus.

Fig. 61. Skull, lateral view:

1 — parietal tuber; 2 — coronal suture; 3 — frontal bone; 4 — HEAD of the mandible (mandibular condyle); 5 — zygomatic process; 6 — coronoid process; 7 — styloid process; 8 — tympanic part; 9 — mastoid part; 10 — squamous part of the temporal bone; 11 — occipital bone; 12 — lambdoid suture; 13 — temporal line; 14 — parietal bone

The nasal cavity (cavum nasi) has superior, inferior, and lateral walls. The nasal cavity is divided by a septum into two symmetrical halves. The perpendicular plate of the ethmoid bone and the Vomer serve as the partition. The bony septum is supplemented by Cartilage. The anterior aperture of the nasal cavity is called the piriform aperture. The inferior wall, or floor, of the nasal cavity is formed by the hard palate. The nasal cavity has no posterior wall; it terminates in the choanae, which connect it to the nasopharynx. The lateral walls of the nasal cavity are formed by the body of the maxilla, the ethmoidal labyrinth, the perpendicular plate of the palatine bone, and the medial plate of the pterygoid process of the sphenoid bone. In each part of the nasal cavity, there are three nasal meatuses: superior, middle, and inferior. The superior and middle nasal meatuses are formed by the conchae of the ethmoid bone, while the inferior nasal meatus is formed by a facial skull bone — the Inferior nasal concha. The ethmoidal labyrinths and the sphenoidal sinus open into the superior nasal meatus. The frontal and maxillary sinuses, as well as the anterior ethmoidal Cells, open into the middle one. The nasolacrimal canal opens into the inferior nasal meatus.

The nasal cavity is bordered on all sides by the sinuses of the neurocranium and viscerocranium bones, which, together with the nasal cavity, act as sound resonators for the human vocal apparatus.

Skull buttresses (craniofacial buttresses). In certain areas of the skull, there are bony thickenings known as buttresses. They attenuate shocks and mechanical impacts during walking, running, jumping, blows sustained during certain sports (e.g., boxing), and the pressure exerted during chewing movements. There are 4 recognized buttresses.

The frontonasal buttress begins on the maxilla at the canine and adjacent Teeth, extends superiorly along the frontal process of this bone, and reaches the margin of the nasal part of the frontal bone.

The zygomaticoalveolar (zygomaticomaxillary) buttress originates from the alveolar thickenings of the first two molars and extends upward from the zygomatic bone to the temporal bone, where it abuts its zygomatic process, and superiorly to the frontal bone.

The pterygopalatine buttress is formed by the pterygoid process of the sphenoid bone and the perpendicular plate of the palatine bone.

The mandibular buttress is a thickening of the body of the mandible. Through the mandibular head, the pressure generated during food chewing or when pressing the mandible against the maxilla is transmitted to the temporal bone.

Connections of the skull bones. The BONES OF THE skull are immovably joined together by sutures. In youth, these sutures are a type of syndesmosis, whereas in adulthood they become synostoses. The only movable bone of the skull is the mandible (lower jaw), which articulates with the temporal bone via the temporomandibular joint.

Depending on their structure, sutures can be plane, squamous, or serrate. Plane sutures connect the facial bones, while serrate sutures join the bones of the cranial vault (the parietal, occipital, and frontal bones). Squamous sutures are found where the temporal bones meet the parietal bones.

Based on their shape, the sutures include the coronal, sagittal, and lambdoid sutures.

The temporomandibular joint is formed by the mandibular fossa and the articular tubercle of the temporal bone, along with the condylar process of the mandible. An articular disc divides the joint cavity into two isolated chambers, making it a bicompartmental joint. Furthermore, the right and left temporomandibular joints function as a combined joint, meaning isolated movements cannot occur in just one of them.

The joint is reinforced by accessory ligaments. It permits movements such as elevation and depression of the jaw, as well as lateral displacement—actions essential for mastication and speech.