The ethmoid bone of the skull. Paired and unpaired skull bones

Paired and unpaired bones of the skull form the skeleton of the head. Some elements have a spongy structure, others are mixed and flat. Next, consider what the skull consists of. The name of the bones, their location will also be described in the article.

General information

Two sections are distinguished in the skull. They are different in their functions and development. The bones of the child’s skull have their own characteristics. The brain section forms a cavity for the brain and for a number of sensory organs. It contains the bones of the cranial vault and its base. In the second (front) department, almost all the senses are located. The initial segments of the digestive and respiratory systems are also present here.

Brain

It has eight bones. Two of them are paired. These are temporal and parietal elements. The remaining bones are unpaired. The brain has some features. The bones of the cranial vault are represented by the outer and inner plates of the compact substance and the spongy structure located between them. The latter is called "diploe". This substance penetrate the channels in which diploic veins are present.

The outer plate has a smooth surface. It is covered by the periosteum. The segment of the same name of the inner plate is represented by the hard shell of the brain. It is thin and includes a large number of organic and inorganic compounds. In this regard, this element is brittle and brittle. With cranial injuries, his fracture occurs more often than damage to the outer plate.

The periosteum has a strong fusion with the bones in the joints. The rest of the length of the connection is quite loose. The periosteum limits the cellular space within the borders of one bone. In this area, the formation of hematomas and ulcers is likely.

The inner surface of the brain

There are impressions and elevations in it. They correspond to the furrows and convolutions of the brain. Here, the areas of fit of the sinuses and vessels of the hard shell are also distinguished. Holes are present in some areas of the skull. They are intended for emissory veins, which connect the venous sinuses of the membrane, external and diploic vessels. The largest openings are considered mastoid and parietal. Some segments, such as the frontal bone of the skull, contain cavities. They are lined with mucous membranes and filled with air. The same structure is characteristic of the ethmoid, temporal and sphenoid bones, as well as the upper jaw. These elements are called airborne.

Skull frontal bone

She is involved in the formation of the roof and base, surfaces of the nasal cavity and orbits. In adults, this is an unpaired skull bone. It distinguishes between the scales and the nose. It also includes the orbital region. Elongated zygomatic processes are present laterally in the lower parts of the bone. Upward from each of them lies the temporal line. It delimits the surface of the temple from the front of the frontal scales. The processes from the segment are connected with similar ones extending from the cheekbones.

Scales

This is the largest bone site. Scales are formed from two halves. Parts are connected through the frontal suture. By the age of five, he usually overgrows. In some cases, the suture is maintained, and the frontal segment remains divided. In scales distinguish between external and internal surfaces. The first is smooth, has a convex shape. On both sides of the seam, a frontal tubercle (paired) is visible. Under it, on both sides, there is a crescent-shaped roller (superciliary arch). Its shape and size depend on the individual structural features of the skeleton of the head. Between the superciliary arches and tubercles a smooth surface is formed - the glabella.

The outer side of the scales is separated from the orbital region by the infraorbital margin (paired). Approximately in its center there is a notch. Inside it is a frontal groove. In some cases, this notch goes into the hole. A nerve and blood vessels run through it. The inside of the scale is concave. Arterial grooves pass on the surface, in the center - a crest. There are also impressions of convolutions. The frontal crest passes into the sulphuric superior sine groove. At the beginning of the elevation from below there is a blind hole. Granulation pits from the arachnoid membrane are located on the sides of the furrow.

Orbital region

It is represented by a bone plate of a quadrangular irregular shape. It distinguishes between the lower (orbital) and upper (cerebral) surfaces. The first - smooth - is oriented to the orbit. In its anterolateral zone, the dimple of the lacrimal gland is located, medially and in front, a block recess. The brain part, directed into the cranial cavity, contains impressions of the convolutions and elevations between them.

Nose section

This part is located between the orbital zones. It is represented by a bone site, which borders the lattice notch on the sides and front. The lateral and posterior edges are articulated with the edge of the plate, and the front side is with the nasal elements and the maxillary process. In this place there is an acute spine of the nose. She is involved in the formation of the septum. In the rear sections of the bow are cells. They come in contact with similar openings in the ethmoid bone. As a result, their roof is formed.

On each side between the edge of the ethmoid notch and the nasal spine there is a sinus aperture. It leads into the left and right halves of the hole. In adults, the size of the sinus is different. It is lined with mucous membranes. The frontal sinus opens into the middle nasal passage.

Ossification

The development of the frontal bone comes from two centers. They form by the end of the second month of the prenatal period near the infraorbital margin. The frontal bone of the newborn includes two separate elements. They connect to the second year of the postpartum period. Up to five years, a seam between the halves usually remains noticeable.

The ethmoid bone of the skull

It consists of two plates. One is horizontal, the other is perpendicular. Also, this unpaired skull bone includes a maze. This formation is represented by air cells. The labyrinth is a paired segment. The cells on each side are adjacent to the plate and communicate with each other, as well as with the nasal cavity. The ethmoid bone of the skull is in the notch. The plate of the element belongs to the brain. The remaining parts that make up the ethmoid bone of the skull are involved in the formation of the medial sides of the orbits and the walls of the nasal cavity.

The horizontal plate at the back is articulated with a wedge-shaped element. Front and sides, it is attached to the frontal bone. There are many holes in the plate. They are intended for the passage of processes of the olfactory nerves. In the central line from the plate, the so-called cockscomb extends upward. The front end of the cerebral sickle joins it. In front of the ridge lies a paired process - the wing. The perpendicular plate has a hexagonal irregular shape. It forms the anterior region of the septum of the nose.

Maze

Its cells are divided into three groups. They are separated from each other, but fuzzy. Allocate the back, front and middle groups. From the lateral side, they are covered by a thin orbital plate. It is oriented into the cavity of the orbit with its free surface. From the inside, only an insignificant part of the cells is covered by bone plates. Most of them remain open. They are covered by the adjacent frontal, palatine, lacrimal and sphenoid bones, as well as the upper jaw.

The medial side of the labyrinth limits the upper region of the nasal cavity. It has two thin plates - shells (middle and upper). There is also a hook-shaped process. There is a gap between the sinks - this is the upper nasal passage. In some cases, one more is found behind and slightly above the upper recess - the highest. The shells, which include the lattice of the skull, vary in shape and size, determining the different lengths and depths of the corresponding nasal passages.

The skeleton of the head

The cranial vault in the anterior section has a frontal bulge. On it there are elevations: superciliary arches and tubercle. The back of the roof is formed by the scales of the occipital bone. On its sides parietal elements close it. From the zygomatic process in the frontal bone, the temporal arcuate line runs along the roof. From above, it limits the fossa, which, in turn, is separated by the infratemporal crest from the eponymous groove.

Connection of elements

The bones of the skull articulate (the table below briefly shows the types of accession) continuously for the most part. The main types of adjunction are synchondrosis and syndesmosis. The lower jaw is attached by the temporomandibular joint, and the sublingual element is attached through muscle fibers. Syndesmoses are fibrous joints in the form of a variety of sutures. As a rule, their names are formed according to the connected bones. However, there are also seams that have their own names. For example, the articulation of the parietal bones is carried out by means of the sagittal, parietal and frontal - coronary suture and so on.

Synchondrosis is presented as cartilage. They are found mainly on the skull base. Syndesmosis of newborns is also represented by connective tissue membranes. They are called fontanels.