Human Anatomy: Lecture Notes - Savchuk O.I. 2017

Skeleton of the Head. The Skull

Lecture Outline

1. BONES OF THE neurocranium

2. Bones of the viscerocranium

3. Articulations of the cranial bones

4. The Skull as a whole

The bones of the HEAD collectively form the skull. It houses the Brain and several Sensory Organs (sight, smell, taste). In addition, the cranial bones support the initial PARTS OF THE respiratory tract (Nasal cavity) and the Digestive System (Oral Cavity). The skull is divided into the neurocranium and the viscerocranium.

The neurocranium is formed by two paired bones: the temporal and parietal bones, and four unpaired bones: the frontal, ethmoid, sphenoid, and occipital bones.

The viscerocranium is formed by six paired bones: the Maxilla, nasal, lacrimal, zygomatic, palatine, and Inferior nasal concha, and two unpaired bones: the Mandible and Vomer. The Hyoid bone is also included here.

Bones of the neurocranium

The Occipital bone. It consists of the following parts: the squamous, basilar, and lateral parts. All these parts surround the foramen magnum, which connects the cranial cavity with the vertebral canal.

On the Inferior surface of the basilar part is the pharyngeal tubercle, and on its upper surface is the clivus. The internal surface of the squama features the groove for the superior sagittal sinus, the internal occipital protuberance, the internal occipital crest, the groove for the sigmoid sinus, and the groove for the transverse sinus.

The canal of n. hipogioss: (hypoglossal canal) passes through the lateral part of the foramen magnum. The jugular process and jugular notch are located on the internal surface.

On the external surface of the occipital squama, the external occipital protuberance and the nuchal lines (highest, superior, and inferior) are visible.

The Parietal bone is a quadrangular, concave bony plate that has four borders, four angles, and internal and external surfaces.

It has frontal, occipital, squamous, and sagittal borders, as well as frontal, occipital, sphenoidal, and mastoid angles.

The external surface features the superior and inferior temporal lines, while the internal surface features the grooves for the superior sagittal and sigmoid sinuses, arterial grooves, and the parietal foramen.

The Frontal bone consists of the squama, paired orbital parts, and an unpaired nasal part. It is a pneumatic bone containing the frontal sinus.

The nasal part features the nasal spine, the ethmoidal notch, and the frontal sinus. The orbital part contains the lacrimal fossa and the trochlear fovea.

The external surface of the frontal squama features the frontal eminence, the superciliary arch, the glabella, and the supraorbital margin and foramen (or notch). The temporal surface of the squama features the temporal line and the zygomatic process. The internal surface of the squama contains the sagittal groove and the foramen cecum.

The Ethmoid bone lies deep within The Skull and contributes to The formation of the nasal cavity and the orbits. It consists of the perpendicular, orbital, and cribriform plates. On either side of the perpendicular plate are the air-filled ethmoidal Cells. Hanging into the nasal cavity from the Medial surface of the labyrinths are the superior and middle nasal conchae.

The cribriform plate features the crista galli and cribriform foramina.

The Sphenoid bone is located between the occipital and frontal bones at the Base of the neurocranium. It consists of a body and three paired processes: the greater wings, lesser wings, and pterygoid processes. The superior orbital fissure lies between the greater and lesser wings, transmitting Vessels and nerves. The greater wings have cerebral, orbital, maxillary, and temporal surfaces, with the infratemporal crest located on the latter. At the base of the greater wings are three foramina: rotundum, ovale, and spinosum. The foramen rotundum transmits the second branch of the Trigeminal nerve, and the foramen ovale transmits the third branch. The optic canal runs through the base of the lesser wing.

The pterygoid process has lateral and medial plates, and features the pterygoid and scaphoid fossae, the pterygoid (Vidian) canal, and the pterygoid notch. The superior surface of the body features a depression called the sella turcica, which houses the Pituitary Gland, an important endocrine gland. The sphenoidal sinus is located within the body.

The Temporal bone is a paired bone that forms part of the base and lateral wall of the skull. Three parts are distinguished in the temporal bone:

1) Squamous part - pars squamosa.

2) Tympanic part - pars tympanica.

3) Petrous part - pars petrosa.

The temporal bone houses the middle and Inner ear.

The squamous part (pars squamosa) contributes to the Formation of the lateral walls of the skull. It is a convex, vertically oriented plate with a rounded margin that overlaps the corresponding margin of the parietal bone like a fish scale. The zygomatic process projects from the squamous part, articulating with the temporal process of the Zygomatic bone to form the zygomatic arch. The squamous part has cerebral and temporal surfaces; the latter features the groove for the middle temporal artery, the mandibular fossa, and the articular tubercle.

The tympanic part (pars tympanica) is a small, curved plate that bounds the external acoustic opening on three sides. The continuation of this opening is the external acoustic meatus. It is separated from other parts by the tympanomastoid, tympanosquamous, petrotympanic, and petrosquamous fissures.

The petrous part (pyramid), or pars petrosa, is shaped like a three-sided pyramid and has three surfaces: the inferior (facing the exterior of the skull), and the anterior and posterior, which face the cranial cavity, as well as three borders: superior, posterior, and anterior.

The anterior surface of the pyramid features the roof of the tympanic cavity (tegmen tympani), while the apex of the pyramid contains the trigeminal impression for the trigeminal nerve.

The posterior surface of the pyramid contains the external acoustic opening, which leads into the internal acoustic meatus.

The inferior surface of the petrous part contains the jugular fossa, the petrosal fossula, the stylomastoid foramen, and the external opening of the carotid canal.

The base of the pyramid continues into the mastoid process, which contains air cells that communicate with the tympanic cavity.

The pyramid of the temporal bone contains canals and canaliculi:

1) Carotid canal;

2) Facial canal;

3) The musculotubal canal begins near the apex of the pyramid and runs into the tympanic cavity;

4) Caroticotympanic canaliculi;

5) Canaliculus for the chorda tympani;

6) Mastoid canaliculus;

7) Tympanic canaliculus.

Bones of the facial Skeleton

The bones of the facial skeleton include the inferior nasal concha, Lacrimal bone, Nasal bone, vomer, zygomatic bone, Palatine bone, maxilla, mandible, and hyoid bone.

The inferior nasal concha is a paired, independent bony plate that projects into the nasal cavity from the lateral wall, consisting of a body and three processes.

The lacrimal bone (os lacrimale) is a paired, thin, and fragile quadrilateral plate located on the medial wall of the Orbit. It contributes to the formation of the nasolacrimal canal.

The nasal bone (os nasale) is paired and shaped like an elongated quadrilateral plate. It forms the bony bridge of the Nose.

The vomer is an unpaired, trapezoidal bony plate that contributes to the formation of the bony nasal septum.

The palatine bone (os palatinum) is paired and consists of a perpendicular and a horizontal plate, which contribute to the formation of the walls of the nasal and oral cavities, the orbit, and the pterygopalatine fossa.

The zygomatic bone (os zygomaticum) connects the bones of the neurocranium and viscerocranium (frontal, temporal, and maxillary), reinforcing the facial skeleton. It has lateral, temporal, and orbital surfaces, and two processes: frontal and temporal.

The maxilla is a paired bone consisting of a body and four processes (frontal, zygomatic, alveolar, and palatine). Within the body is the maxillary sinus, which communicates with the nasal cavity through the maxillary hiatus. The body of the maxilla features orbital, anterior, infratemporal, and nasal surfaces. The orbital surface contains the infraorbital margin and. The anterior surface features the infraorbital foramen, the canine fossa, and the nasal notch. The infratemporal surface contains the alveolar foramina and canals, and the maxillary tuberosity. The nasal surface features the lacrimal groove, the maxillary hiatus, and the greater palatine groove.

The incisive canal is located on the palatine process. The alveolar process features the alveolar arch, dental alveoli (which contain the Teeth), and interalveolar septa and alveolar eminences between the teeth.

The mandible is an unpaired bone and the only movable bone of the skull. It consists of a body and two rami. Each ramus ends in a coronoid process and a condylar process, separated by the mandibular notch. The head of the mandible is located on the condylar process. On the inner surface of the rami is the mandibular canal, which opens as the mental foramen on the outer surface of the body. The body bears the alveolar process, where the lower teeth are housed within the dental alveoli (sockets), separated by interalveolar septa.

The body of the mandible has a base, on the outer surface of which are the mental protuberance, the mental foramen, and the oblique line. On the inner surface are the digastric fossa, the mental spine, the mylohyoid line, and the sublingual and submandibular fossae. At the junction where the ramus meets the body is the angle of the mandible. On its outer surface is the masseteric tuberosity, and on its inner surface is the pterygoid tuberosity, where the corresponding masticatory Muscles attach.

The hyoid bone is located in the anterior region of the neck between the mandible and the Larynx, and consists of a body and two pairs of horns (cornua) — greater and lesser.

Connections of the skull bones

Three types of sutures:

1) Serrate suture — between the frontal and parietal bones, between the parietal bones, and between the occipital and parietal bones

2) Squamous suture — between the temporal and parietal bones

3) Plane suture — between the facial bones.

Temporomandibular joint. Formed by the head of the mandible and the mandibular fossa of the temporal bone, it is a combined joint. Inside the joint, There is a disc that divides the joint cavity into two compartments (upper and lower). Movements include elevation, depression, lateral deviation (right and left), protrusion, and retrusion: all these movements occur during mastication and speech.

The skull as a whole

Calvaria, base, flat bones consist of two plates with spongy bone in between.

The inner plate is called the glassy plate (lamina vitrea) because it fractures more easily than the outer one.

Base of the skull

The anterior cranial fossa is separated from the middle cranial fossa by the posterior border of the lesser wings and the tuberculum sellae of the sphenoid bone; the middle cranial fossa is separated from the posterior by the superior border of the petrous part of the temporal bone and the dorsum sellae. The anterior fossa contains the foramen cecum, crista galli, and cribriform plate. The middle fossa contains the optic canal, superior orbital fissure, prechiasmatic and carotid grooves, sella turcica, hypophyseal fossa, and the rotundum, ovale, spinosum, and lacerum foramina. The posterior cranial fossa contains the foramen magnum, clivus, jugular foramen, internal acoustic meatus, facial and hypoglossal canals, internal occipital protuberance, grooves for the superior and inferior petrosal sinuses, and grooves for the superior sagittal, sigmoid, and transverse sinuses.

In the region of the facial skeleton

On the anterior surface are the orbit, nasal cavity, and oral cavity. On the lateral surface are the infratemporal and pterygopalatine fossae.

The orbit houses the Eyeball, the lacrimal gland, and the Accessory apparatus of the eye. It has four walls: superior, inferior, lateral, and medial, which are formed by the bones of the skull.

The superior orbital fissure opens into the middle cranial fossa, as does the optic canal. The inferior orbital fissure communicates with the pterygopalatine fossa.

The nasal cavity occupies a central position in the facial skeleton, serves as the initial part of the respiratory tract, and contains the Organ of Smell. It has an inlet and two outlets (choanae). The bony nasal septum consists of the vomer and the perpendicular plate of the ethmoid bone, dividing the nasal cavity into two halves. It features superior, inferior, medial, and lateral walls. On the lateral wall are the superior, middle, and inferior nasal conchae. Beneath these conchae, the superior, middle, inferior, and common nasal meatuses are formed. Beneath the superior nasal concha is the superior nasal meatus. It communicates with the pterygopalatine fossa through the sphenopalatine foramen, with the anterior cranial fossa (through the cribriform plate), with the sphenoid sinus and the ethmoidal labyrinth, and with the orbit (through the posterior ethmoidal foramen).

The middle nasal meatus receives the openings of the maxillary sinus, the frontal sinus, and the middle and anterior ethmoidal air cells. The inferior nasal meatus communicates with the orbit through the nasolacrimal duct. The common nasal meatus is a cleft-like space between the conchae and the nasal septum. It communicates with the oral cavity through the incisive canal.

Oral cavity. It has a superior wall (bony — the hard palate), and anterior and lateral walls (formed by the alveolar processes of the jaws and the teeth).

On the lateral surface of the skull, there are paired fossae: temporal, infratemporal, and pterygopalatine. The boundary between the temporal and infratemporal fossae is the zygomatic arch (laterally) and the infratemporal crest (medially). The infratemporal fossa transitions into the pterygopalatine fossa. The latter communicates with the cranial cavity, the orbit, and the nasal and oral cavities.

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