The ethmoid bone is a small bone in the skull that separates the nasal cavity from the brain. It is lightweight due to its spongy, air-filled construction and is located at the roof of the nose and between the two orbits. The ethmoid bone forms the medial wall of the orbit, the roof of the nasal cavity, and due to its central location it articulates with numerous bones of the viscerocranium.
Inside the neurocranium it articulates with the frontal and sphenoid bones. The frontal bone borders two other neurocranial bones—the parietal bones through the coronal sutures and the sphenoid bone through the sphenofrontal suture. It also articulates with the zygomatic and nasal bones and the maxilla. The viscerocranium face includes these bones: vomer, 2 inferior nasal conchae, 2 nasals, maxilla, mandible, palatine, 2 zygomatics, and 2 lacrimals.
The viscerocranium or facial bones supports the soft tissue of the face. The viscerocranium consists of 14 individual bones that fuse together. However, the hyoid bone, ethmoid bone, and sphenoid bones are sometimes included in the viscerocranium.
The two zygomatic bones form the cheeks and contribute to the orbits. They articulate with the frontal, temporal, maxilla, and sphenoid bones. The two lacrimal bones form the medial wall of the orbit and articulate with the frontal, ethmoid, maxilla, and inferior nasal conchae. The lacrimal bones are the two smallest bones located in the face. The two slender nasal bones located in the midline of the face fuse to form the bridge of the noise and also articulate with the frontal, ethmoid and maxilla bones.
The inferior nasal conchae are located within the nasal cavity. They are spongy and curled in shape; their primary function is to increase the surface area of the nasal cavity, which also increases the amount of air that contacts the mucous membranes and cilia of the nose, thus filtering, warming, and humidifying the air before it enters the lungs.
At the base of the nasal cavity is the small vomer bone which forms the nasal septum. The maxilla bones fuse in the midline and form the upper jaw. They provide the bed for the upper teeth, the floor of the nose, and the base of the orbits. The maxilla articulates with the zygomatic, nasal, lacrimal, and palatine bones.
The palatine bones fuse in the midline to form the palatine, located at the back of the nasal cavity that forms the roof of the mouth and the floor of the orbit. Finally, the mandible forms the lower jaw of the skull. The joint between the mandible and the temporal bones of the neurocranium, known as the temporomandibular joint, forms the only non-sutured joint in the skull. Facial bones : There are fourteen facial bones.
Some, like the lacrimal and nasal bones, are paired. Others, like the mandible and vomer, are singular. The orbit, or eye socket, is the cavity located in the skull in which the eye and its associated appendages are housed.
The orbits are conical, sometimes described as four-sided pyramidal, cavities that open in the midline of the face and point backwards. To the rear of the orbit, the optic foramen opens into the optical canal through which the optic nerve and ophthalmic artery pass.
The primary functions of the orbit include protection of its delicate contents and, through muscle attachment and a smooth coating fascia, to also promote the smooth, delicate movements of the eye. The orbital cavity is formed from seven bones. The frontal bone forms the superior border of the orbital rim and also the superior wall roof of the orbital surface. The zygomatic bone forms the lateral and half of the basal border of the orbital rim, and also the lateral wall of the orbital surface—this is the thickest region of the orbit as it is most exposed to external trauma.
Completing the basal and medial border of the orbital rim is the maxillary bone, which also forms the inferior wall floor of the orbital surface. The lacrimal and ethmoid bones contribute to the medial wall of the orbit and also to the medial wall of the orbital canal. The small palatine bone contributes to the floor of the orbit. Finally, the sphenoid bone forms the posterior wall of the orbit and also contributes to the formation of the optic canal.
The human skull has numerous holes known as foramina through which cranial nerves, arteries, veins, and other structures pass. Base of the skull upper surface : This image details the foramina of the skull. In anatomy, a foramen is any opening.
Foramina inside the body of humans and other animals typically allow muscles, nerves, arteries, veins, or other structures to connect one part of the body with another. The human skull has numerous foramina through which cranial nerves, arteries, veins, and other structures pass. The skull bones that contain foramina include the frontal, ethmoid, sphenoid, maxilla, palatine, temporal, and occipital lobes.
A suture is a type of fibrous joint or synarthrosis that only occurs in the skull or cranium. A suture is a type of fibrous joint or synarthrosis that only occurs in the skull. A small amount of movement is permitted through these sutures that contributes to the compliance and elasticity of the skull. The joint between the mandible and the cranium, known as the temporomandibular joint, forms the only non-sutured joint in the skull.
Most sutures are named for the bones that they articulate. At birth, many of the bones of the skull remain unfused to the soft spots described as fontanelle. The bones fuse relatively rapidly through a process known as craniosynotosis, although the relative positions of the bones can continue to change through life.
In old age the cranial sutures may ossify completely, reducing the amount of elasticity present in the skull. As such, the degree of ossification can be a useful tool in determining age postmortem.
Lateral view of a skull showing sutures : The dotted red lines indicate the location of skull sutures. The paranasal sinuses four, paired, air-filled spaces surround the nasal cavity, and are located above and between the eyes, and behind the ethmoids.
Skull Sinuses : This image shows the position of the sinuses in the human skull. Paranasal sinuses are a group of four, paired, air-filled spaces that surround the nasal cavity maxillary sinuses , above the eyes frontal sinuses , between the eyes ethmoid sinuses , and behind the eyes sphenoid sinuses.
The sinuses are named for the facial bones that they are located behind. Log In. Sign Up. Become a Gold Supporter and see no ads. Log in Sign up. Articles Cases Courses Quiz. About Recent Edits Go ad-free. Edit article. View revision history Report problem with Article.
Citation, DOI and article data. Wong, A. Occipital bone. Reference article, Radiopaedia. URL of Article. On this page:. Quiz questions. The neurocranium consists of the occipital bone, two temporal bones, two parietal bones, the sphenoid, ethmoid, and frontal bones—all are joined together with sutures. Evolutionary,it is the expansion of the neurocranium that has facilitated the expansion of the brain and its associated developments.
Neurocranium : A lateral view showing the bones that structure the neurocranium. The occipital bone forms the base of the skull at the rear of the cranium. It articulates with the first vertebra of the spinal cord and also contains the foramen magnum, the large opening of the skill through which the spinal cord passes as it enters the vertebral column.
The occipital bone borders the parietal bones through the heavily serrated lambdoidal suture, and also the temporal bones through occipitomastoid suture.
The temporal bones are situated at the base and sides of the skull, lateral to the temporal lobes of the brain. The temporal bones consist of four regions the squamous, mastoid, petrous and tympanic regions. The squamous region is the largest and most superior region. Inferior to the squamous is the mastoid region, and fused between the squamous and mastoid regions is the petrous region.
Finally, the small and inferior tympanic region lies anteriorly to the mastoid. The two large parietal bones are connected and make up part of the roof and sides of the human skull.
The two bones articulate to form the sagittal suture. In the front, the parietal bones form the coronal suture with the frontal bone, and in the rear, the lambdoid suture is formed by the occipital bone. Finally, the squamosal suture separates the parietal and temporal bones. The sphenoid bone is situated in the middle of the skull towards the front and forms the rear of the orbit.
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