The ethmoid bone is a bone of very spongy substance, somewhat irregularly cubical in shape, lying at the root of the nose, between the two orbits or eye-sockets, and forming part of the bony wall of both. The segment of the ethmoid bone which forms part of the inner wall of the orbital cavity is called the orbital plate, while another segment, forming the roof and back part of the septum of the nasal cavity is called the perpendicular plate. Two irregularly shaped, shell-like projections from the ethmoid bone are called the superior and middle turbinate (conchae), and form ledges on the inside wall of the nasal cavity. Research Ethmoid Bone
The frontal bone is one of the flat cranial bones that forms the forehead and roof of the orbits. The frontal bone also forms the upper part of the nasal cavity as well as forming the floor of the skull, where the brain is housed. Two cavities, the frontal sinuses, lie within the frontal bone, just behind the spots above each orbit. The frontal bone is attached to the parietal bones by the coronal suture, and is also connected by sutures to the sphenoid, ethmoid bone, maxillary, nasal, lachrymal, and zygomatic bones. In the center of the front of the frontal bone, just between and slightly above the orbits, is a raised portion of the bone, called the glabella. The frontal bone also features two foramina. one just above each orbit. Research Frontal Bone
The maxilla is one of the primary facial bones and defines much of the face below the orbits and above the jawbone. The maxilla (with the ethmoid bone, frontal bone, and zygomatic bones) forms much of the lateral walls of the nasal cavity, the orbital cavity, and part of the cheek. The
maxilla also mounts the top row of teeth in a non-movable foundation, so that chewing is enabled by moving the mandibular teeth against them. The outer wings of the maxilla, where it meets the zygomatic bones, are called the zygomatic processes. The upper part of the
maxilla, which forms the lower, inner surface of the orbit cavity, is called the orbital surface of the
maxilla, while the exterior surface, just between the orbit and the nasal cavity, is called the frontal process of the
maxilla. The roof of the mouth is formed by the palatine bone, which is attached to the maxilla just behind the teeth. Research Maxilla
The nasal cavity is in the middle of the face and is formed by a number of bones. The nasalbone forms the roof, while the sides are formed by the ethmoid bone and maxillary bones. Within the
nasal cavity is a vertical plate, or septum which divides the cavity into two halves. The top and front of the septum is made of the vertical plate of the ethmoid bone, while the bottom and back of the septum is formed by the vomer. Each side of the nasal cavity features three curved ledges, called turbinates or conchae. The superior and middle turbinates are protrusions from the ethmoid bone, while the inferior turbinate is attached to the maxillary bone. The back of the
nasal cavity opens just behind the palatine bone. Research Nasal Cavity
The orbit, or eye socket, is formed by the juncture of a number of bones. Of these, the sections of the ethmoid bone are located between the orbits, forming part of the inner wall of each orbital cavity (called the orbital plate) and lateral wall and part of the roof of the nasal cavity. The frontal bone forms most of the upper surfaces, while the maxilla and zygomatic bone form the lower and outer surfaces. The lachrymal bone also forms part of the inner surface, in conjunction with the ethmoid bone. Research Orbit
The palatine bones consist of a vertical part and a horizontal plate and make up part of the orbital floor, the nasal cavity, and the back part of the palate. The two palatine bones are joined at the palate at the median palatine suture. Each bone is pierced by one greater palatine foramen and two lesser palatine foramina. Each palatine bone is also articulated with the vomer, and the conjunction of these bones forms the posterior nasal spine. The vertical portions of each palatine bone articulate with the inferior nasalconcha and the ethmoid bone. The horizontal plates of the palatine bones also join the two palatine processes of the maxilla bones, at the transverse palatine suture. Research Palatine Bones
The large pterygoid processes of the sphenoid bone are located at the rear of the posterior nasalaperture. Each pterygoid process features a hamulus (at the tip of a flat protrusion called the medial pterygoid plate) and a pterygoid fossa, within which is located the pteygoid fissure. The pterygoid process of the sphenoid is located in a critical area, articulating with twelve other bones, including the frontal, occipital, ethmoid bone, vomer, temporals, parietals, palatines, and zygomatics. Research Pterygoid Processes
The skull is one of the principle groups of bones in the human anatomy. The skull consists of twenty-six bones: eight bones form the skull, which houses the brain and ear ossicles, plus fourteen facial bones, which form the front of the face, jaw, nose, orbits, and the roof of the mouth, three more bones make up the inner ear ossicles, and one more, the hyoid bone, is in the neck and is attached to the temporal bone by ligaments and anchors the tongue. The skull also contains a dental arcade of teeth, which are technically not bones, though they do share some of the compositional characteristics of bonetissue. Children may grow twenty deciduousteeth, which will eventually fall out and be replaced by the permanent teeth.
The bones of the skull include the frontal bone, the occipital bone, two parietal bones, and two temporal bones. The lower rearmost part of each temporal bone is called the mastoid process, but because it is separated from the temporal bone, proper, by a suture, it is often considered a separate bone. The sphenoid bone forms the central base of the skull and spans the skull from side to side, the greater wings forming side plates of the skull. The sections of the ethmoid bone are positioned between the orbits, forming the walls and roof of the nasal cavity, while the three middle ear ossicles (stapes, malleus, and incus) are located within the temporal bones on each side of the skull. The U-shaped hyoid bone is found in the neck, and is attached by ligaments to the temporal bones. In the face, the two maxillary bones form much of the orbits, nose, upper jaw and roof of the mouth, while the zygomatic bones form the cheeks. The lachrymal bones are located on the inner sides of the orbits and are attached to the ethmoid bone and maxillary bones. Within the nasal cavity, the vomer is located in the low center and forms the thin flat bone of the nasalseptum, while two inferior urbinates form the lower sides of the cavity and two palate bones form the floor of the nasal cavity as well as the roof of the mouth.
The mandible is the only movable part of the skull, forming the lower jaw and mounting the teeth. The bones of the skull, with the exception of the mandible, are held together by very thin sutures, or seams, in which the periosteum of the individual bones interweave with each other, and are cemented by a fibrous, connective tissue. In the newborn, these sutures are not yet developed, with the bones being attached by cartilage which ossifies over time as the bones of the skull fuse together. The most evident external sutures of the skull include the coronal suture, joining the frontal bone and parietal bone, the sagittal suture, joining the parietal bones to each other, the lambdoid suture, joining the occipital and parietal bones, the squamous suture, joining the temporal and sphenoid bones to the parietal bone on each side of the skull.
The pterion is the short segment of the suture joining the squamous and parietal bones. The bones of the skull also feature a number of sinuses and foramina. Four pairs of sinuses flank the nasal cavity. Two are found in the maxillary bone, and are called maxillary sinuses. The sphenoid bone forms two paranasal sinuses called the sphenoids, and the ethmoid bone forms the two paranasal sinuses called ethmoids. Additionally, the frontal sinuses are located in the frontal bone just behind the roof of each orbit. The foramen magnum is a large, round opening in the base of the skull which admits the spinal cord, while at the base of each temporal bone is the external auditory meatus, which serve as the auditory canals. Just above each orbit in the frontal bone is a small notch or hole, called a supraorbital foramen, and just below each orbit, in the maxillary bone, is an infraorbital foramen. Two more openings, one on each side of the skull, can be found in the frontal processes of the zygomatic bones, and are called zygomatofacial foramina.
On each side of the mandible, just below the lower canines, are the mental foramina. These facial foramina serve to admit blood vessels and nerves through and into the bone. The teeth are mounted in the maxillary bone and the mandible, and are brought together for chewing by the hinge-like motion of the mandible. An average adult will have thirty-two teeth, evenly arrayed on the maxilla and mandible. Research Skull
The vomer is the thin, flat bone which forms the bottom and back portion of the bony septum in the nasal cavity. The vomer supports the perpendicular plate of the ethmoid bone, which forms the upper portion of this septum. The vomer extends past the palatine bone in the back of the mouth cavity, where its rearmost section, the ala, connects to the pterigoid process of the sphenoid bones and the forward section of the occipital bone, just in front of its basilar part. Research Vomer
The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
Abbreviations
Research Ethmoid Bone
