The cranium (skull) is the skeletal structure of the head that supports the face and protects the brain. It is subdivided into the facial bones and the cranial bones. The facial bones underlie the facial structures, form the nasal cavity, enclose the eyeballs, and support the teeth of the upper and lower jaws. The cranial bones surround and protect the brain and house the middle and inner ear structures.
In the adult, the skull consists of 22 individual bones, 21 of which are immobile and united into a single unit. The 22nd bone is the mandible (lower jaw), which is the only moveable bone of the skull.
The Facial Bones
The facial bones (facial skeleton or viscerocranium) consist of 14 individual bones. They underlie the facial structures, form the nasal cavity, enclose the eyeballs, and support the teeth of the upper and lower jaws.
- Inferior nasal conchae (2).
- A pair of curved bony plates that projects into the nasal cavity space from the lower lateral walls.
- Lacrimal bones (2).
- A pair of small, rectangular bones that form the anterior, medial wall of the orbits.
- Mandible (1).
- A U-shaped bone that forms the lower jaw.
- Maxilla (2).
- A pair of bones that together form the upper jaw, much of the hard palate, the medial floor of the orbit, and the lateral base of the nose.
- Nasal bones (2).
- A pair of small bones that form the bridge of the nose and support the lateral nasal cartilages.
- Palatine bones (2).
- L-shape bones that form parts of the orbits, nasal cavity, and the roof of the mouth (hard palate).
- Vomer (1).
- A triangular-shaped bone and that forms the posterior-inferior part of the nasal septum.
- Zygomatic bones (2).
- A pair of irregular-shape bones that form the prominence of the cheeks and much of the lateral walls and floor of the orbits.
The Cranial Bones
Eight cranial bones that form the braincase (neurocranium), which encloses and protects the brain.
- Ethmoid (1).
- A bone that 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. On the interior of the skull, the ethmoid also forms a portion of the floor of the anterior cranial cavity.
- Frontal (1).
- A bone that forms the anterior skull (forehead).
- Occipital (1).
- A bone that forms the posterior skull and posterior base of the braincase.
- Parietal (2).
- A pair of bones that form most of the upper lateral sides of the skull.
- Sphenoid (1).
- A bone that forms much of the base of the central skull and extends laterally to contribute to the sides of the skull.
- Temporal bone (2).
- A pair of bones that form the lower lateral sides of the skull.
The rounded top of the braincase is called the calvaria, and the floor is referred to as the base of the skull. The interior of the braincase is called the cranial cavity.
The skull base is a complex area that varies in-depth and has numerous openings for the passage of cranial nerves, blood vessels, and the spinal cord. The interior of the skull base is subdivided into three large spaces, called the anterior cranial fossa, middle cranial fossa, and posterior cranial fossa (fossa = “trench or ditch”). From anterior to posterior, the fossae increase in depth. The shape and depth of each fossa correspond to the shape and size of the brain region that each house.
CRANIAL BONES: SUPERIOR VIEW OF THE CALVARIA
CRANIAL BONES: SUPERIOR VIEW OF THE SKULL BAS
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Reference: “The Skull“
Wikipedia, the free encyclopedia
Reference 1: “Human Skull“
Reference 2: “Facial Skeleton“
Reference 3: “Neurocranium“