Anatomy of the Skull

Anatomy of the Skull

• The objectives are to list the bones of the skull, identify the major sutures and surface markings of the skull
• The objectives are to identify the major foramina of the skull and list the major structures which pass through the foramina
• The objectives are to describe the cranial fossa and its part, understand the base of the skull and its fracture, and describe the structure of the mandible

The Skull

• The skull is divided into cranial bones (neurocranium) and facial bones (viscerocranium)
• The cranial bones include one frontal, one ethmoid, one sphenoid, one occipital, two parietal, and two temporal bones
• The facial bones include two maxilla, two zygomatic, two nasal, two palatine, two lacrimal, two inferior conchae, one vomer, and one mandible

Key Bone Landmarks

• Many bones have anatomical landmarks, including the frontal, maxilla, zygomatic, nasal, mandible, and lacrimal

Frontal Bone

• Key landmarks are the squama, supraorbital margin, supraorbital foramen, and frontal sinuses

Occipital Bone

• Key parts are the external occipital protuberance (EOP), external occipital crest, nuchal lines, basilar part, and occipital condyle

Temporal Bone

• Key parts include the squamous, zygomatic process, petrous part, tympanic part, external auditory meatus, mastoid process, and styloid process

Sphenoid Bone

• Landmarks include greater and lesser wings, pterygoid processes, the sella turcica, and the body

Ethmoid Bone

• Key parts are the lateral plate, perpendicular plate, cribriform plate, olfactory foramina, and crista galli

Maxilla

• Parts include the infraorbital foramen, alveolar process, and palatine process

Other Key Bones

• Parietal, temporal, sphenoid, and occipital bones are important to note in the skull

Sutures of the Skull

• Sutures include coronal, sagittal, lambdoid, pterion, bregma, and lambda
• The pterion is the thinnest part of the lateral wall of the skull and is clinically important

Skull Fontanelles

• Fontanelles are 6 spaces between some skull bones in infants, permitting easy brain growth and overlapping of skull bones during labor
• Anterior fontanelle (bregma) closes by 18-24 months of age
• Posterior fontanelle (lambda) closes by 3-6 months
• Anterolateral Fontanelle (Pteryon) and Posterolateral Fontanelle (Asterion) are also key

Cranial Fossa

• Divides into anterior, middle, and posterior cranial fossa

Anterior Cranial Fossa

• Formed of the orbital plate of the frontal bone, cribriform plate of the ethmoid, crista galli, and lesser wing of the sphenoid
• Contains the frontal lobe of the cerebrum, optic nerves, and olfactory bulb and tract

Middle Cranial Fossa

• Formed of the greater wing of the sphenoid, body of the sphenoid, squamous part of the temporal bone, and anterior part of the petrous bone
• Houses the temporal lobe of the cerebrum

Posterior Cranial Fossa

• Formed by the sphenoid part of clivus, posterior part of the petrous bone, and occipital bone
• Displays the groove for the transverse sinus, groove for the sigmoid sinus, and internal occipital protuberance
• Contains the cerebellum and brain stem

Foramina of the Skull

• Key foramina include the optic foramen, superior orbital fissure, foramen rotundum, foramen ovale, foramen lacerum, and foramen spinosum
• Also important are the internal acoustic meatus, hypoglossal canal, and foramen magnum

More Foramina

• Supraorbital, infraorbital, and mental foramina are important
• These features allow structures to pass through

Base of the Skull

• Features include the alveolar process of the maxilla, central incisor teeth, choana, zygomatic arch, mandibular fossa, and spine of the sphenoid
• Others include the styloid process, jugular foramen, occipital condyles, condylar (hypoglossal) canal, and foramen magnum

Fractures

• Fractures involving the cribriform plate result in epistaxis and cerebrospinal rhinorrhea
• Fractures involving the orbital plate of the frontal bone result in subconjunctival hemorrhage and exophthalmos
• Fractures of the base of the skull are most common where it is weakest and where the middle ear and sphenoidal air sinuses are vulnerable

Battle’s Sign

• Battle's sign is an indication of fracture of the middle cranial fossa of the skull, and may suggest underlying brain trauma
• Appears as a result of extravasation of blood along the path of the posterior auricular artery

The Mandible

• Key features of the mandible include the head (condylar process), mandibular notch, coronoid process, ramus, angle, and body
• More features are the mylohyoid line, submandibular fossa, digastric fossa, mandibular foramen, and mental foramen