The Structures of the Skull

by Robert Tallitsch, PhD | September 15, 2021

Blog and video explanation of the bones and sutures of the cranium and craniosynostosis with symptoms, causes, treatments and a patient case example!

Written by: Robert Tallitsch, PhD

My first gross anatomy class at the University of Wisconsin-Madison was taught by Dr. David L. Langebartel, and amazing dissector and teacher. It was through his teaching that I came to realize that one needed to start with a firm understanding of the skull in order to completely understand the soft tissues of the head.

It is impossible to discuss the entire anatomy of the skull in the space allowed, so let me introduce you to some of the anatomical highlights. These highlights should start you well on your way towards understanding the anatomy of the skull.

It is easiest to learn the anatomy of the skull by learning the anatomy of the cranium first, followed by learning the anatomy of the facial skeleton and the foramina of the skull.

The Cranium

The skull possesses five large cavities — four of which, the paired nasal cavities and the paired orbits, open to the exterior and are part of the facial skeleton. The cranial cavity is the fifth, and largest cavity. It houses the brain and, except where the brain and spinal cord are continuous at the foramen magnum, the cranial cavity is completely closed.

The cranium is composed of eight bones: the paired parietal and temporal bones, and the singular frontal, ethmoid, sphenoid, and occipital bones. These bones protect the brain and the special sense structures related to hearing, balance, smell, and vision.

The bones of the cranium are joined at immovable joints termed sutures.

The frontonasal suture joins the frontal bone with the superior aspects of the two nasal bones.
The frontal bone is joined posteriorly to the two parietal bones by the coronal suture.
The sagittal suture joins the right and left parietal bones.
Laterally, the parietal bones are joined to the temporal bones by the squamous suture.
The two parietal bones are joined posteriorly to the occipital bone by the lambdoid suture.

The Cranial Floor

The interior shape of the cranium follows the contours of the brain. The curving depressions within the cranial floor are termed cranial fossae. The anterior cranial fossa holds the frontal lobes of the cerebral hemispheres. It is formed by the contours of the frontal bone, ethmoid, and the lesser wings of the sphenoid. The middle cranial fossa is formed by the sphenoid, temporal, and parietal bones. It supports the temporal lobes of the cerebrum. The posterior cranial fossa supports the occipital lobes of the cerebral hemispheres as well as the cerebellum, pons, and medulla oblongata. This fossa is primarily formed by the occipital bone, along with some contributions from the parietal and temporal bones.

Several prominent landmarks are associated with the floor of the cranium. The first two are found between the right and left sides of the anterior cranial fossa, on the superior surface of the ethmoid. The cribriform plate is the part of the ethmoid perforated by the cribriform foramina. Branches of the olfactory nerve, which carry sensations of smell, pass through these foramina.

The crista galli is the prominent ridge separating the right and left portions of the cribriform plate.

The next landmark is found between the right and left portions of the middle cranial fossa. The sella turcica is located on the superior portion of the sphenoid. This structure encloses the hypophyseal fossa, which houses the pituitary gland.

The foramen magnum is the largest foramen of the skull. It is found within the posterior cranial fossa. The junction between the brain stem and the spinal cord occurs at the foramen magnum.

The prominent jugular foramina are located at the junction of the occipital and temporal bones, slightly lateral and anterior to the foramen magnum. The internal jugular vein and the glossopharyngeal, vagus and accessory cranial nerves pass through each of these foramina.

The Facial Skeleton

The bony structure of the face is formed by six pairs of bones (maxillae, palatine, nasal, inferior nasal conchae, zygomatic, and lacrimal) and two singular bones (vomer and mandible).

Two of the most complex portions of the face are the orbits and the nasal complex.

The superciliary ridge (supraorbital ridge) of the frontal bone is usually palpable immediately superior to the orbit. These ridges are typically more prominent on the skull of a male than that of a female.

The Orbits

The orbits house and protect the eyes. However, these structures also house the muscles that move the eyes, blood vessels, nerves, the lacrimal glands, and adipose tissue.

The roof of each orbit is formed by the frontal bone, with most of the floor being formed by the maxilla. Moving from lateral to medial within the orbit one finds the lateral mass of the ethmoid (which articulates with the sphenoid and a small process of the palatine bone), the lacrimal, and the maxilla. Most of the posterior wall of the orbit is formed by the sphenoid.

Several foramina are associated with each orbit. Here is a listing of the structures that pass through those foramina:

The infra-orbital and the maxillary nerves, as well as the infra-orbital artery pass through the infra-orbital foramen.
The maxillary nerve passes through the infra-orbital fissure.
The oculomotor, trochlear, ophthalmic, and abducens nerves, and the ophthalmic vein pass through the superior orbital fissure.
The optic nerve and the ophthalmic artery pass through the optic canal (optic foramen).
The supra-orbital nerve, ophthalmic nerve and supra-orbital artery pass through the supra-orbital foramen (supra-orbital notch).

The Nasal Complex

The nasal complex, which encloses the nasal cavity and paranasal sinuses, is composed of cartilage and seven bones. The superior wall of the nasal cavity is composed of the frontal bone, sphenoid, and ethmoid. The bony portion of the nasal septum is composed of the vomer and the perpendicular plate of the ethmoid, while the lateral portion of the nasal cavity is composed of the maxillae, lacrimal bones, ethmoid, and the inferior nasal conchae. The bridge of the nose is supported by the nasal bones and maxillae.

The Mandible

The mandible, which forms the lower jaw, is the largest and heaviest bone of the face. It is composed of the body of the mandible and the ramus of the mandible on each side. The condylar processes of the mandible extend upward to the smooth head of the mandible, which articulates with the condylar fossa of the temporal bone. This articulation between the head of the mandible and the condylar fossa forms the temporomandibular joint (TMJ).

Several prominent foramina and fossae are seen on the mandible. The mental foramina penetrate the anterior surface of the body of the mandible. Sensory nerves pass through these foramina carrying sensory information from the lower lips and chin. The submandibular fossa, which is the site of the submandibular salivary gland, is found on the medial surface of the mandible. Finally, the mandibular foramen (mandibular fossa) leads to the mandibular canal, which carries blood vessels and nerves that serve the lower teeth.

Summary

Knowing and understanding the anatomy of a structure as complex as the brain can be managed if one breaks the many topics down into manageable groups. It is more important to have a solid knowledge of the skull as a whole, to know the way the bones of the skull fit together, and know the major foramina and which structures pass through these foramina than it is to have a detailed understanding of the anatomy of each bone of the skull.

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