0.7 Skeletal sysyem module 8: the skull  (Page 4/101)

The two suture lines seen on the top of the skull are the coronal and sagittal sutures. The coronal suture    runs from side to side across the skull, within the coronal plane of section (see [link] ). It joins the frontal bone to the right and left parietal bones. The sagittal suture    extends posteriorly from the coronal suture, running along the midline at the top of the skull in the sagittal plane of section (see [link] ). It unites the right and left parietal bones. On the posterior skull, the sagittal suture terminates by joining the lambdoid suture. The lambdoid suture    extends downward and laterally to either side away from its junction with the sagittal suture. The lambdoid suture joins the occipital bone to the right and left parietal and temporal bones.

Facial bones of the skull

The facial bones of the skull form the upper and lower jaws, the nose, nasal cavity and nasal septum, and the orbit. The facial bones include 14 bones, with six paired bones and two unpaired bones. The paired bones are the maxilla, palatine, zygomatic, nasal, lacrimal, and inferior nasal conchae bones. The unpaired bones are the vomer and mandible bones. Although classified with the brain-case bones, the ethmoid bone also contributes to the nasal septum and the walls of the nasal cavity and orbit.

Maxillary bone

The maxillary bone    , often referred to simply as the maxilla (plural = maxillae), is one of a pair that together form the upper jaw, much of the hard palate, and the base of the nose (see [link] ). Each tooth is anchored into a deep socket called an alveolus. . The hard palate    is the bony plate that forms the roof of the mouth and floor of the nasal cavity, separating the oral and nasal cavities.

Maxillary bone

Zygomatic bone

The zygomatic bone    is also known as the cheekbone. Each of the paired zygomatic bones forms much of the wall of the orbit.

Nasal bone

The nasal bone    is one of two small bones that articulate (join) with each other to form the bony base (bridge) of the nose. They also support the cartilages that form the lateral walls of the nose (see [link] ). These are the bones that are damaged when the nose is broken.

Lacrimal bone

Each lacrimal bone    is a small, rectangular bone that forms the anterior, medial wall of the orbit This bone contains the nasalacrimal canal, through which tears pass.

Vomer bone

The unpaired vomer bone, often referred to simply as the vomer, is triangular-shaped and forms the lower part of the nasal septum (see [link] ).

Mandible

The mandible    forms the lower jaw and is the only moveable bone of the skull. At the time of birth, the mandible consists of paired right and left bones, but these fuse together during the first year to form the single U-shaped mandible of the adult skull.

Isolated mandible

Paranasal sinuses

The paranasal sinuses    are hollow, air-filled spaces located within certain bones of the skull ( [link] ). All of the sinuses communicate with the nasal cavity (paranasal = “next to nasal cavity”) and are lined with nasal mucosa. They serve to reduce bone mass and thus lighten the skull, and they also add resonance to the voice. This second feature is most obvious when you have a cold or sinus congestion. These produce swelling of the mucosa and excess mucus production, which can obstruct the narrow passageways between the sinuses and the nasal cavity, causing your voice to sound different to yourself and others. This blockage can also allow the sinuses to fill with fluid, with the resulting pressure producing pain and discomfort.

The paranasal sinuses are named for the skull bone that each occupies. The frontal sinus    is located just above the eyebrows, within the frontal bone (see [link] ). The largest sinus is the maxillary sinus    . These are paired and located within the right and left maxillary bones, where they occupy the area just below the orbits. The maxillary sinuses are most commonly involved during sinus infection because of their close connection to the nasal cavity. The sphenoid sinus    is a single, midline sinus. The ethmoid bone contains multiple small spaces separated by very thin bony walls. These are collectively called the ethmoid sinus .

Paranasal sinuses

Hyoid bone

The hyoid bone is an independent bone that does not contact any other bone and thus is not part of the skull ( [link] ). It is a small U-shaped bone located in the upper neck near the mandible, with the tips of the “U” pointing backwards. The hyoid serves as the base for the tongue above, and is attached to the larynx and the pharynx .

Hyoid bone

References

Centers for Disease Control and Prevention (US). Injury prevention and control: traumatic brain injury [Internet]. Atlanta, GA; [cited 2013 Mar 18]. Available from: (External Link) .