Skull, head, cranial vault, dome, noodle, and thinker are all words that are used to describe the same thing: the cranium. The skull is part of the axial skeleton and is divided into the two sections: the facial bones and the cranium. It is comprised of the cranium, which is round and houses the brain, and the facial bones which form the upper and lower jaws, the nose, orbits, and other facial structures. The adult skull is made up of 22 bones; 21 of them are immovable and the 22nd one is the mandible, the lower jaw, and is the only moveable bone of the skull. The cranial bones form the cranial cavity which holds and protects the brain.
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The cranium is composed of eight bones: the frontal bone, two parietal bones, two temporal bones, the occipital bone, the sphenoid bone, and the ethmoid bone. A suture is an synarthrosis joint, an immoveable joint, between the bones and is how the bones of the cranium are connected. They are fibrous joints. There are four major sutures that connect the bones of the cranium together: the frontal or coronal, the sagittal, the lambdoid, and the squamous. The frontal suture connects the frontal bone to the two parietal bones. The sagittal suture connects the two parietal bones. The lambdoid connects the two parietal bones to the occipital bone. The squamous sutures connect the parietal bones to the temporal bones.
The Frontal Bone
The frontal bone, as seen below in pink, is the anterior roof of the skull, the bone of the forehead, and extends down to be the superior portion of the orbits, the top of the eye sockets. It articulates (is connected to) with the parietal, sphenoid, ethmoid, nasal, lacrimal, maxillary, and zygomatic bones. The shape of the frontal bone plays a big part in the visual identity of a person. The supra-orbital margin is the superior, upper, rim of the eye socket. It has supra-orbital foramina, sometimes a notch, above each supra-orbital margin that allow blood vessels and nerves to reach the eyebrows, eyelids, and frontal sinuses. Supra meaning superior, orbital meaning eye socket, and foramen meaning hole; the name of the describes what it is and where it is. The smooth part above and between your eyebrows has a name and is called the glabella. The zygomatic process of the frontal bone connects with the frontal process of the zygomatic bone which help form the cheekbone.
An anterior view of the skull
The Parietal Bone
The parietal bones, the right parietal bone highlighted in green below, make the roof of the cranium. It forms the upper lateral side of the skull. The parietal bones articulate with one another, and with the frontal, sphenoid, temporal, and occipital. The superior and inferior temporal lines are low ridges that mark the attachment sites of the temporalis muscle.
Lateral view of the right parietal bone
The Temporal Bone
The temporal bones are the lower lateral sides of the skull as seen below in green. They are the bones one’s ears sit upon. There are many features of the temporal bones. First, there is the zygomatic process. It connects to the temporal process of the zygomatic bone. Together these form the zygomatic arch, the cheekbone. Next, there is the mastoid process. It is a pyramidal projection at the back of the temporal bone. It can easily be felt on the side of one’s head, behind the earlobe. It is a site of muscle attachment for muscles including sternocleidomastoid, splenius capitis, and longissimus capitis. The mandibular fossa of the temporal bone is a depression that articulates with the mandible; they form the temporomandibular joint. This allows for the opening and closing of the jaw. The temporal fossa is a depression in the temporal region. It is one of the largest landmarks of the skull. The frontal bone, sphenoid bone, parietal bone, and temporal bone all contribute to the concavity of the fossa. The temporal lines are the superior border and the zygomatic arch is the inferior border. It is a site of muscle attachment for temporalis, a mastication (chewing) muscle. Next, there is the styloid process. It is posterior to the mandibular fossa. It is a pointy, stylus like process that is just below the ear. It is an attachment point for muscles and tendons of the neck and tongue. The external auditory or acoustic, meatus or canal, is the canal the funnels sound into the eardrum. It is the large opening on the lateral side of the skull often associated with the ear. It is a tube running from outer ear to the middle ear. The internal auditor, or acoustic, meatus or canal is a bony canal within the petrosal portion of the temporal bone that allows nerves and vessels from within the posterior cranial fossa to the brain. It connects the middle and inner ear cavities to the temporal bone.
Lateral view of the skullThe Occipital Bone
The occipital bone, highlighted in green below, is the bone the makes up the posterior and base portion of the cranium. The large oval opening in the base is the foramen magnum. It is where the spinal cord exits the skull. There are two oval shaped occipital condyles, one on each side of the foramen magnum. These are where the skull connects to the first cervical vertebrae of the vertebral column, atlas. At the midline of the bone, there is a protrusion called the external occipital protuberance, the tip of it is referred to as the inion. It is easy to find and palpate. This can vary in size in people. It is a site of attachment for a ligament of the posterior neck. Lateral to either side of the protrusion is the superior nuchal line. This is the most superior site for muscle attachment, with only the scalp covering the skull above the lines. Just inferior to the external occipital protuberance there is the inferior nuchal line, also a site of muscle attachment.
A posterior inferior view the the skullThe Sphenoid BoneA superior and posterior view of the sphenoid bone
The Sphenoid bone, above, is a cranial bone shaped like a butterfly. It is located in the anterior portion of the cranium, as seen below in green. It forms the base of the anterior skull and spreads laterally enough to contribute to the sides of the skull. It consists of a central body that is cubical-shaped and two sets of wing-shaped extensions that project laterally: the greater wings and the lesser wings. The sella turcica (Turkish saddle) is located at the midline of the middle cranial fossa. It is named for the resemblance to a horse’s saddle. The hypophyseal (pituitary) fossa is the depression of the base of the sella turcica and houses the pituitary gland. The greater wings, also known as Ala major, extend out laterally from the sella turcica to form the anterior floor of the middle cranial fossa. They are a pair of larger winged structures of the bone, curved upwards, backward and on the lateral sides. The lesser wings, also known as Ala minor, are a pair of the smaller projections that are flat, triangular structures situated anterior to the greater wings. Projecting inferiorly on the posterior side are the media pterygoid plate and lateral pterygoid plate. The right and left medial pterygoid plates form the posterior, lateral walls of the nasal cavity. The larger lateral pterygoid plates serve as attachment sites for chewing muscles.
An anterior lateral view of the skullThe Ethmoid BoneAn anterior view of the ethmoid bone
The ethmoid bone is located between the two orbits and at the roof of the nose. It forms the roof and lateral walls of the upper nasal cavity, the upper portion of the nasal septum, and contributes to the medial wall of the orbit. What makes it a cranial bone is that inferiorly it forms a portion of the anterior cranial floor. It separates the nasal cavity from the brain. It is made up of the perpendicular plate, the crista galli (rooster’s comb or crest), and the cribriform plate, as seen above. The perpendicular plate forms the superior portion of the nasal septum. The ethmoid bone also forms the lateral walls of the upper nasal cavity, extending from each lateral wall are the superior nasal concha and middle nasal concha, which are thin, curved projections that extend into the nasal cavity. The crista galli is a superior bony projection that serves as an attachment point for a covering layer of the brain. On either side of the crista galli is the cribriform plate. It forms the roof of the nasal cavity and contributes to the anterior cranial fossa. It is a small, flattened area with many small openings, olfactory foramina. Small nerve branches from the olfactory areas of the nasal cavity pass through these openings to enter the brain. You can see it highlighted in green below from a superior lateral view through the cranium.
A superior lateral view of the ethmoid boneCranial Cavity
The inner surface of the cranial cavity is divided into three distinct depressions. It is comprised of the anterior, middle, and posterior cranial fossae. Each fossa accommodates a different part of the brain. The anterior cranial fossa is the most shallow and superior of the three fossae. The fossa is comprised of the frontal bone, the ethmoid bone, and the body and lesser wings of the sphenoid bone. It houses the anteroinferior portion of the frontal lobe. The middle fossa is made up of the greater wings of the sphenoid bone and the temporal bone. It can be said to be butterfly shaped. It houses the pituitary gland and the two lateral parts of the fossa contain the temporal lobes. The posterior cranial fossa is made up of mainly the occipital bone and the posterior section of the temporal bones. It houses the brainstem and cerebellum as well as associated arteries and nerves.
A superior and lateral view of the inside of the cranium
A mnemonic to remember the bones of the cranium is PEST OF.
To see more about the bony landmarks of the skull which are used for radiological or anthropological skull measurements see: https://radiopaedia.org/articles/skull-landmarks
This video describes the bones of the cranium and face and shows them on a model. From 3:50 onward are the cranial bones. https://www.youtube.com/watch?v=0N20150qthA
HyoidThis horseshoe-shaped bone is used as a solid foundation for the tongue to move. This bone also has many areas for muscle attachment. The muscles above the hyoid are referred to as the suprahyoid muscles. The muscles below the hyoid are referred to as the infrahyoid muscles. For more information on these muscles, refer to the neck muscles section. There are 3 main parts of the hyoid: the body, the greater horn, and the lesser Horn. There is one major feature which is the tubercle of the greater horn.