Development of the skull in the postnatal period. Development of the skull Embryonic development of the skull of its stages
The secondary bones of the human skull include: the occipital (except for the upper part of the scales), the sphenoid (without the internal plate of the pterygoid process), the ethmoid and conchae, the pyramid and mastoid process of the temporal, the auditory ossicles (malleus, incus, stapes) and the body of the hyoid bone.
The skull develops partly on the basis of the pre-existing cranial part of the dorsal chord and its derivative, partly from derivatives of the gill arches. The bony skull is formed after the appearance of the brain, nerves and blood vessels and is formed around them. This is the reason for the formation of a large number of holes and channels in the skull, which serve for the passage of blood vessels and nerves.
Development of the brain part of the skull. The formation of the skull in mammalian embryos begins with the accumulation of mesenchyme around the dorsal chord (notochord) at the level of the hindbrain, from where it spreads under the anterior and superior parts of the brain, forming the base for the developing brain and its roof. This primary mesenchymal cover of the skull later turns into membranous connective tissue, desmocranium (membranous stage of skull development). Parts of the membranous skull are preserved in separate places after birth in the form of fontanelles. At the 2nd - 4th month of development, a number of cartilages appear around the anterior end of the dorsal chord: parachordal, cartilagines parachordales (occipital, cartilago occipitalis, wedge-shaped, cartilagines sphenoidalis, etc.), as well as cartilaginous cases, containers for the organs of smell, vision and hearing: nasal , visual and auditory capsules.
Figure: Development of the skull.
1 - nasal capsule; 2 - visual capsule; 3 - auditory capsule; 4 - parachordal cartilage; 5 - dorsal string (chord); 6 - cranial crossbars.
Parachordal cartilages penetrate to the location of the future pituitary gland. The above individual cartilages merge with each other as they develop, as well as with the nasal, optic and auditory capsules. As a result, a continuous cartilaginous plate of the base of the skull, chondrocranium, is formed, with a median opening for the pituitary gland. At this stage (the second half of the 3rd month), the skull is a formation in which there is a cartilaginous base in the form of a narrow groove. The rest of the skull is connective tissue (cartilaginous or primary skull).
At the next stage of skull development, ossification of the cartilaginous base and membranous roof occurs and the formation of the bone skull, osteocranium. The process of development and formation of the bones of the skull, like the rest of the bones of the skeleton, occurs in a certain sequence. According to certain periods of intrauterine development of the fetus, ossification nuclei appear in the connective tissue and cartilaginous anlages of future bones. Spreading in depth and along the surface, the ossification nuclei merge with each other, forming the outer and inner plates of the compact bone substance and the spongy substance located between them.
Not all cartilaginous formations undergo ossification. A number of cartilages remain in adults (cartilages of the wings of the nose, the cartilaginous part of the nasal septum and small cartilages of the base of the skull).
Different parts of some bones develop differently: some - in place of cartilage, others - in place of connective tissue (for example, the squama of the occipital bone develops as a primary bone, the remaining parts - as secondary bones). With age, parts of bones and individual bones fuse with each other, causing the total number of skull bones to decrease.
Development of the facial part of the skull. The facial part of the skull develops mainly from the gill arches. In aquatic vertebrates, gill arches are located metamerically in the spaces between the gill slits through which water passes to the gills - the respiratory organs of these animals.
In vertebrates that live on land, gill slits are present only in the embryonic period. The number of gill arches varies in different aquatic animals: in terrestrial vertebrates they are formed in the amount of 6; a person develops 5 arches, with the 5th arch being poorly developed (rudimentary). The 1st (upper) is called the mandibular, or mandibular, arch. The 2nd - by the hyoid, or hyoid, arch, and the rest - by the 3-5th gill arches, respectively.
The development of the facial skull involves the 1st-3rd gill arches and the frontal process, which limits the oral bay, the future oral cavity, from above. The 1st branchial arch on each side forms two processes - maxillary and mandibular, which limit the oral bay from below and from the sides.
Figure: Diagram of the relationship between the derivatives of the gill arches. Cartilaginous and bone elements arising in humans from the branchial arches: the lower jaw, the hyoid apparatus and some cartilages of the larynx and windpipe.
1 - 1st gill arch; 2 - 3rd gill arch; 3 - 4th gill arch; 4 - 5th gill arch; 5 - 2nd gill arch.
The maxillary processes are separated from each other by the frontal process, which during development is divided into three parts: unpaired (middle) and paired (lateral). The organ of vision is located between the maxillary process and the lateral part of the frontal process. Between the lateral parts of the frontal and maxillary processes there is a tear groove. The mandibular processes of the right and left arches are fused.
The formation of the upper and lower jaws occurs around the cartilaginous rudiments of the mandibular arch, one of which is called dorsal, cartilago dorsalis, and the second is called ventral, cartilago ventralis. In lower fish, these two sections of the mandibular arch serve as jaws. In vertebrates, these cartilages are models around which ossifying mesenchyme grows, forming the upper and lower jaws. The maxillary process gives rise to the upper jaw (with the exception of the part corresponding to the area of the incisors of the premaxillary bone), the zygomatic bone, the palatine, the medial plate of the pterygoid process, and the sphenoid bone. The mandibular process will give rise to the lower jaw, which develops periosteally around the disappearing Meckel's cartilage. The middle part of the frontal process forms the vomer, the perpendicular plate of the ethmoid bone and the premaxillary bone. The lateral part of the frontal process serves to form the labyrinth of the ethmoid bone, nasal and lacrimal bones. In addition to these bones, the 1st branchial arch gives rise to the malleus and incus, the 2nd branchial arch forms the stapes, styloid process, small horns of the hyoid bone, the 3rd branchial arch forms the body and large horns of the hyoid bone.
Features of the structure of the newborn’s skull. The skull of a newborn has the following characteristic features:
· the shape and size of the skull, the ratio of its parts differ significantly from the skull of an adult;
· the number of bones is greater than that of an adult;
· between the bones of the roof and base of the skull there are significant layers of membranous connective tissue and cartilage.
The skull of a newborn is very elastic, since numerous parts of the bones are connected to one another by layers of connective tissue. This feature undoubtedly facilitates the adaptation of the fetal head to the osteofibrous ring of the woman’s small pelvis during childbirth, when the edges of the parietal bones overlap each other along the midline, as well as the scales of the frontal and occipital bones onto the parietal bones. As a result, the interparietal and anteroposterior diameters decrease, and the longitudinal size of the head increases. The head circumference is 34 cm, the volume for boys is 375-380 cm 3, for girls it is 350-360 cm 3.
Skull dimensions of a newborn:
The distance between the tubercles of the parietal bones is 9.5 cm
The distance between the external auditory canals is 8 cm
Occipito-frontal size – 11.5 cm
Occipito-mental size – 16 cm
From these dimensions it follows that during childbirth the head should not pass the occipitomental size through the birth canal, otherwise complications arise (Prives M.G., Lysenkov N.K., Bushkovich V.I., 2000; Tegako L. I., Marfina O.V., 2003).
When examining the skull of a newborn from the front, there is a significant development of the cerebral part of the skull compared to the facial part, which accounts for 65% of the length of the head. The facial skull is short and wide, with well-developed eye sockets. This is due to the fact that the eyeball and the auxiliary apparatus of the eye are well developed and prepared to perceive light stimuli. The upper jaw, which has the rudiment of the air sinus and lacks the alveolar process, is small in size. This in turn affects the size of the nasal cavity and nasopharynx, which are presented in the form of a narrow slit. Only with the inclusion of the act of sucking and breathing does muscle function increase, which, together with food and air, has a formative effect on the bones of the skull.
The cranial cavities differ markedly from the cavities of the adult skull. The bone tissue of the external auditory canal is absent and the tympanic cavity with auditory ossicles enclosed in connective tissue is located under the skin (Alekseev V.P., Debets G.F., 1964).
The orbit has the shape of a quadrangular pyramid with a rounded entrance, its diameter is 25-27 mm (in an adult 35-40 mm). The superior and inferior orbital fissures are wide open. Between the bones that form the eye socket are noticeable layers of connective tissue. Due to the poor development of the orbital plate of the ethmoid bone, the medial wall is poorly expressed.
The nasal cavity is represented by a gap 18 mm high and 7 mm wide at the level of the lower nasal meatus; at the upper level - width 3 mm (for an adult, 54, 15 and 10 mm, respectively). The rudiment of the air sinus of the upper jaw communicates with the middle meatus. Other sinuses and cells of the ethmoid bone are absent.
The pterygopalatine fossa is well expressed and communicates with five wide canals.
The temporal fossa is bounded on the medial side by the squama of the temporal bone and the greater wing of the sphenoid bone. The depth of the fossa at the level of the zygomatic process is 12 mm, in an adult it is 2 times greater, although other dimensions of the adult’s skull are several times greater than the dimensions of the skull of a newborn. This indirectly indicates that the masticatory temporal muscle is already quite large and well developed.
Many of the bones of a newborn's skull, which appear as one bone in an adult, consist of separate parts. This feature can be explained not only by the fact that such a mosaic skull adapts more easily to the shape of the birth canal, but also by the fact that it repeats its phylogenetic development. All animals lower than humans have a larger number of bones in the skull.
Rice. 51. Permanent and non-permanent fontanelles (Speransky V.S., 1988)
1 – anterior fontanelle; 2 – posterior: 3 – mastoid; 4 – wedge-shaped; 5 – glabellar; 6 – metopic; 7 – parietal; 8 – cerebellar.
Between individual bones and their parts there are large layers of membranous connective tissue called fontanelles. The layers between the bones at the base of the skull are filled with cartilage.
A newborn has six fontanelles. On the outside, they are covered with skin and the aponeurosis of the head; on the side of the cranial cavity, the dura mater adjoins them. In the area of the fontanelles, the pulsation of the arteries of the brain and membranes is felt, which is why these areas are called pulsating, gushing. The size and size of the fontanelles are subject to significant fluctuations, depending on the rate of ossification of the skull bones. By the time the fontanels close, one can judge mineral metabolism and assess the physical development of the child.
The anterior fontanel is unpaired, usually diamond-shaped, measuring 3.5x2.5 cm. It is bounded by the scales of the frontal bone and two parietal bones. Replaced by bone at the beginning of the 2nd year of life.
The posterior fontanel is unpaired, located between the scales of the occipital bone and the angles of the parietal bones, has a triangular shape with a length of 1 cm. Final closure is observed by the end of the 2nd month after birth.
The sphenoid fontanelle is paired, irregularly rectangular in shape, measuring 0.8x1.2 cm. It is limited by the edge of the anterior lower corner of the parietal bone, the scales of the frontal and temporal bones, and the greater wing of the sphenoid bone.
The mastoid fontanel is paired, somewhat smaller than the previous one. Unlike other fontanelles, it is closed by cartilage. It is located between the lower posterior angle of the parietal bone, the squama of the temporal and occipital bones. The sphenoid and mastoid fontanelles previously closed in the 3rd month after birth. Now, due to the acceleration phenomenon, they are increasingly present in the skull only in immature or premature newborns. In addition, there were additional fontanels that closed in the first days after birth (Fig. 51).
At the base of the newborn’s skull, layers filled with cartilage (synchondrosis) are distinguished between the bones:
· fibrous synchondrosis (paired), limited to the pyramid of the temporal bone and the lateral parts of the occipital bone;
· synchondrosis (paired), located between the apex of the pyramid and the body of the sphenoid bone;
· synchondrosis (paired) between the body of the sphenoid and occipital bones, resulting in the formation of a slope;
· synchondrosis between individual parts of the occipital bone.
The skull undergoes great changes from the moment a child is born until the end of life. These rearrangements are associated with those features of the reaction of connective tissue, in particular bones, that are observed at different age periods of a person’s life. We are primarily interested not in the change in the internal structure of the bones of the skull, but in the transformation of its external shape, although this occurs under the influence of a restructuring of the architecture of the bone.
Changes in the skull can be roughly divided into five age periods.
First period(maximum active growth) covers the age from birth to 7 years. It is characterized by active growth of the skull. In the first 6 months after birth, the volume of the brain skull doubles, and the cranial fossae deepen. In this regard, the occipital region protrudes. Due to the growth of the upper jaw, the nasal cavity also increases in height to 22 mm. In the first year of life, the cartilage in the occipital bone and the membranous tissue of the cranial vault disappear. The formation of seams is planned.
From 1 to 2 years, the volume of the cranium triples, and up to 5 years it reaches 3/4 of the volume of the adult skull. There is a uniform growth of the brain and facial skull, the head becomes wider. The base of the skull reaches the same shape as that of an adult. The diameter of the foramen magnum is finally formed. Due to the growth of teeth and alveolar processes, the height of the upper and lower jaws increases, which is reflected in the shape of the face, oral and nasal cavities. An important point is the formation of sutures, which not only fasten the individual bones of the skull, but also serve as a place for their growth in width.
Early closure of the three main sutures of the skull roof (coronoid, lambdoid and sagittal) leads to the formation of a conical head shape.
Second period(from 8 to 13-14 years) is characterized by a relative slowdown in the growth of the skull bones, although there is a significant increase in the nasal cavity, upper jaw and orbit.
Third period lasts from the beginning of puberty (14-16 years) to 20-25 years, when skeletal growth ends. At this age, the development of the skull is complete. The facial skull grows more intensively relative to the brain, especially in men. The base of the skull increases not only in the transverse, but also in the anteroposterior direction. The air sinuses, tubercles, protrusions, glabella and grooves are formed.
Fourth period(26-45 years) is most stable when there is no change in the size of the skull. Usually during this period, ossification of the sutures occurs. In men, the posterior part of the sagittal suture is closed first, in women - the coronal suture. The mastoid-occipital and lambdoid sutures are then closed. The last thing to disappear is the scaly seam. In dolichocephals, obliteration of sutures occurs earlier than in brachycephals (Khrisanfova E.N., Perevozchikov I.V., 1999).
Fifth period lasts from the moment of suture fusion (45 years) until old age. It is characterized by a noticeable transformation of the facial skull associated with tooth loss. The absence of part or all teeth leads to atrophy of the bone substance of the alveolar processes of the upper and lower jaws. In this case, the shape of the face somewhat resembles that of a newborn. Atrophy of the alveolar processes of bones is reflected in the restructuring of the hard palate, lower and upper jaws, articular fossa and tubercle of the temporal bone, zygomatic process and zygomatic bone. In old people, the thickness of the compact plate and cancellous bone decreases, the skull becomes light in many bones (lacrimal, ethmoid, large wings of the sphenoid bone, tympanic part of the temporal bones); Additional cavities are revealed due to bone resorption. On the contrary, the scales of the frontal bone, against the background of atrophy of other skull bones, are often preserved and are thicker. The chemical composition of bone tissue in older people is significantly different compared to young people. With significant resorption of organic substances, restructuring of architectonics and an increase in the content of mineral salts in the bones, they become more fragile, break and crack with less force compared to the bones of a young person (Alekseev V.P., 1966; Nikityuk B.A., 2000; Tegako L., Kmetinsky E., 2004).
The main reasons for the formative processes of the skull in phylogenesis are the progressive development of the brain, sensory organs and the restructuring of the gill apparatus surrounding the initial sections of the digestive and respiratory systems. Thus, in the lancelet, the rudimentary brain is surrounded by a connective tissue membrane (membranous skull), in cyclostomes the base of the skull is cartilaginous and the roof is connective tissue, in cartilaginous fish there is a cartilaginous skull, in sturgeon fish the cartilage is partially replaced by bone tissue. In the process of evolution, cartilage tissue is gradually replaced by bone tissue, resulting in the formation of a bony skull. There are 7 pairs of gill arches in the visceral skull.
The sense organs and chewing apparatus progress in their development, which have a modeling effect on the formation of the skull.
In terrestrial animals, the gills are reduced, replaced by respiratory organs - the lungs, and the material of the gill arches goes to the formation of the visceral skull.
Thus, the base of the skull in phylogenesis goes through three successive stages of development: connective tissue (membranous), cartilaginous and bone; and the vault (roof) of the skull goes through two stages of development: membranous (connective tissue) and bone. The visceral skull and individual bones of the brain skull develop on the basis of the membranous skull, bypassing the cartilaginous stage. In phylogenesis, the number of skull bones decreases significantly: some disappear completely, others grow together.
The bones of the facial and brain skull develop from various embryonic rudiments. The base and roof of the cranium also have different sources of development.
Development of the brain skull. The brain skull is formed simultaneously with the development of the brain from the sclerotomes of the cephalic somites, which are formed around the cranial end of the notochord.
In the first month of embryogenesis, a webbed skull develops. It consists exclusively of connective tissue, the source of which is the mesenchyme, covering the brain in the form of a case. The roof of the skull is formed from these structures (the frontal, parietal bone, squama and tympanic part of the temporal bone, the upper part of the squama of the occipital bone are of connective tissue origin).
At the beginning of 2 months, a cartilaginous base appears. Parachordal plates are formed near the head end of the notochord, and prechordal cartilaginous plates are formed in front of them.
At the end of 2 months, the cartilaginous base of the skull is formed, and the cartilaginous regions are formed: ethmoid, orbital, labyrinth and occipital. From the ethmoidal region the ethmoid bone and the inferior turbinate are formed. Most of the sphenoid bone develops from the orbital region. The labyrinthine region is the cartilaginous basis for the development of the petrous part and mastoid process of the temporal bone. From the basilar region the basilar, lateral parts and the lower part of the squama of the occipital bone develop.
Development of the facial skull. The facial skull develops from the mesenchyme adjacent to the cranial part of the primitive gut. Gill arches form in the mesenchyme between the gill pouches. The first arch is called the mandibular arch, and the second is called the hyoid arch. These two arches are called visceral, and the rest are called gills.
From the first visceral arch, two auditory ossicles develop: the malleus and the incus, and the formation of the lower jaw also occurs.
The second visceral arch in its middle part is reduced, turning into the stylohyoid ligament.
The remaining bones of the facial skull are endesmal. They develop from buds in the mesenchyme located on the sides and in front of the nasal capsules. An exception is the inferior turbinate, which develops from remnants of cartilage in the area of the nasal capsule.
Consequently, the bones of the facial skull, except for the hyoid bone, inferior turbinate, coronoid and condylar processes of the mandible, are primary.
7. Development of the brain part of the skull. Variants and anomalies of its development.
Brain section of the skull develops from the mesenchyme surrounding the rapidly growing brain. The mesenchymal cover turns into a connective tissue membrane - the stage of the membranous skull. In the area of the arch, this shell is subsequently replaced by bone. Cartilaginous tissue appears only at the base of the skull, near the anterior section of the notochord, which ends dorsal to the pharynx, posterior to the future pituitary stalk. The areas of cartilage lying next to the notochord are called perichordal (parachordal) cartilages, and in front of the notochord are the prechordal plates and cranial crossbars. Subsequently, the cartilage at the base of the skull is replaced by bone, with the exception of small areas (synchondrosis), which persist in adults until a certain age.
Thus, in humans, the vault (roof) of the skull goes through two stages in its development: membranous (connective tissue) and bone, and the base of the skull goes through three stages: membranous, cartilaginous and bone.
Frontal bone. In approximately 10% of cases, the frontal bone consists of two parts, with a frontal suture remaining between them, sutura frontlis (sutura metopica). The size of the frontal sinus varies, very rarely the sinus is absent.
Sphenoid bone. Failure of fusion of the anterior and posterior halves of the body of the sphenoid bone leads to the formation of a narrow, so-called craniopharyngeal canal, in the center of the sella turcica. The foramen ovale and foramen spinosum sometimes merge into one common foramen; the foramen spinosum may be absent.
Occipital bone. The upper part of the occipital squama, in whole or in part, can be separated from the rest of the occipital bone by a transverse suture. As a result, a special triangular bone is identified - the interparietal bone, os in- terparietdle.
Ethmoid bone. The shape and size of the cells of the ethmoid bone are very variable. The highest nasal concha is often found, concha nasdlis suprema.
Parietal bone. Due to the fact that the ossification points do not merge, each parietal bone can consist of an upper and lower halves.
Temporal bone. The jugular notch of the temporal bone can be divided into two parts by the interjugular process. If there is the same process in the jugular notch of the occipital bone, a double jugular foramen is formed. The styloid process of the temporal bone may be absent, but more often it is long, and can even reach the hyoid bone in the case of ossification of the stylohyoid ligament.
8. Development of the facial part of the skull. The first and second visceral arches, their derivatives.
Facial part of the skull develops from the mesenchyme adjacent to the initial part of the primary intestine.
The facial part of the skull develops from the mesenchyme adjacent to the initial part of the primary intestine. In the mesenchyme between the gill pouches, cartilaginous gill arches are formed. The first two of them are of particular importance - the visceral arches, on the basis of which the visceral skull develops.
First visceral arch (maxillary) in humans, it gives rise to two auditory ossicles (the malleus and the incus) and the so-called Meckel’s cartilage, on the basis of which the lower jaw develops from the mesenchyme.
Second visceral arch (hyoid) consists of two parts - upper and lower. From the upper part develop the auditory ossicle - the stapes and the styloid process of the temporal bone. The lower part goes to the formation of the small horns of the hyoid bone. The large horns and body of the hyoid bone are formed from the third visceral (I branchial) arch.
Thus, on the basis of the visceral arches from the connective tissue, the small bones of the facial part of the skull and the lower jaw develop.
| Parameter name | Meaning |
| Article topic: | SKULL DEVELOPMENT |
| Rubric (thematic category) | Education |
The skull goes through 3 stages of development: membranous, cartilaginous and bony. The membranous and cartilaginous stages are temporary for higher mammals and humans. Οʜᴎ transform into one another and to some extent correspond to constant forms in phylogeny. The membranous stage in humans begins at the end of the 2nd week of the embryonic period, the cartilaginous stage - from the 2nd month. The date of the beginning of the bone stage and, therefore, the end of both the membrane-
that and the cartilaginous stage in different parts of the skull are different. Thus, in the lower jaw, the ossification point appears on the 39th day, and in the basilar part of the occipital bone - on the 65th day of intrauterine development. In the brain skull, the bones or parts of bones involved in the formation of the base of the skull go through 3 stages of development. In the bones of the calvarium, the bony stage immediately follows the membranous stage. Most of the bones of the facial skull also bypass the cartilaginous stage, and only a few of them go through all 3 stages of development. Based on their origin, all skull bones are divided into primary, developing from connective tissue, and secondary, arising on the basis of the cartilaginous bone model.
Primary bones: the upper part of the occipital scales, the squamosal and tympanic parts of the temporal bone, the parietal and frontal bones, the medial plate of the pterygoid process of the sphenoid bone, the palatine bone, the vomer, the nasal, lacrimal, zygomatic bones, the upper and lower jaws. Secondary bones: occipital (except for the upper part of the occipital squama), sphenoid (without the medial plate of the pterygoid process), ethmoid bones, inferior turbinates, pyramid and mastoid process of the temporal bone, auditory ossicles (malleus, incus, stirrup) and body of the hyoid bone.
The skull develops on the basis of the cranial part of the notochord and the mesenchyme surrounding it and the rudiment of the brain, as well as from derivatives of the branchial ducts. The membranous skull contains a series of openings and canals for the passage of nerves and blood vessels, and the future occipital bone contains a large opening for the spinal cord. As the brain, nerves and blood vessels further develop, the bone skull is formed around them, due to which many holes and channels are formed in it, serving for the passage of blood vessels and nerves (Table 1).
The development and formation of the bones of the skull, like other bones of the skeleton, occur in a certain sequence. In the membranous and cartilaginous anlages of future bones, centers (points) of ossification appear at appropriate times. Spreading over the surface and in depth, they merge with each other and form the outer and inner plates of the compact bone substance and the spongy substance located between them. Not all cartilaginous formations of the skull undergo ossification. In adults, the cartilage of the wings of the nose, the cartilaginous parts of the nasal septum and the small cartilages of the base of the skull are preserved.
Table 1. Timing of the appearance of ossification centers in the bones of the skull (according to B.M. Patten, 1959)
There are more skull bones in a fetus and a newborn than in an adult. The number of bones decreases as a result of the fusion of several bones into one. The newly formed bone may consist of parts of different origins, ᴛ.ᴇ. Primary bones are connected to secondary bones. For example, the squama of the occipital bone develops as a primary bone, the remaining parts as secondary bones.
Development of the brain skull
The formation of the skull begins with the accumulation of mesenchyme around the notochord at the level of the hindbrain. From here the mesenchyme spreads beneath the anterior and superior parts of the brain, forming the base and vault of the receptacle for the developing brain. This primary mesenchymal cover later develops into the membranous skull (leptocranium). After birth, areas of the membranous skull are preserved in the form of fontanelles. The cartilaginous stage begins at the 2-4th month of intrauterine development, when parachordal and prechordal cartilaginous crossbars appear around the anterior end of the chord, as well as cartilaginous cases - containers for the organs of smell, vision, hearing (nasal, visual and auditory capsules) (Fig. 7) . Parachordal
Rice. 7. Development of the skull (2-3rd month of embryogenesis):
a - top view: 1 - nasal capsule; 2 - visual capsule; 3 - prechordal cartilage; 4 - auditory capsule; 5 - parachordal cartilages; 6 - chord; b - left view: 1 - pituitary fossa; 2 - parachordal cartilage; 3 - chord; 4 - III cervical vertebra; 5 - body of the II cervical vertebra; 6 - anterior arch of the 1st cervical vertebra
Rice. 8. Development of the brain skull; cartilaginous skull (second half of the 3rd month): 1 - cartilaginous skull
cartilage penetrates to the location of the future pituitary gland. As development progresses, individual cartilages merge with each other, as well as with the nasal, optic and auditory capsules, due to which a continuous cartilaginous plate with a median opening for the pituitary gland is formed at the base of the skull (Fig. 8). During this period (the second half of the 3rd month), the skull has a cartilaginous base and a membranous vault - the so-called cartilaginous skull (chondrocranium) is formed. At the next stage of skull development, ossification of the membranous vault and cartilaginous base and the formation of the bone skull, osteocranium, occur (Fig. 9-11).
Rice. 9. Ossification of the cranial vault:
1 - brain vesicles; 2 - ossification point of the squama of the occipital bone; 3 - cartilaginous skull; 4 - ossification point of the frontal scales
Rice. 10. The next stage of ossification of the cranial vault:
1 - primary bones of the cranial vault;
2 - cartilaginous skull
Rice. 11. Ossification centers of the occipital (a, b), sphenoid (c) and temporal (d) bones
Development of the facial skull
The bones of the facial skull develop from the gill arches and the frontal process, which bounds the oral bay on top - the future oral cavity. In aquatic vertebrates, gill arches are located metamerically in the spaces between the gill slits through which water passes, washing the gills - the respiratory organs. In vertebrates living on land, in the embryonic period, gill arches (accumulations of mesenchyme) are formed, and instead of gill slits, gill pouches are formed between them. Terrestrial vertebrates have 6 gill arches, humans have 5, and the 5th gill arch is poorly developed (vestigial). The 1st gill arch is usually called the mandibular arch, and the rest are called the 2-5 gill arches, respectively. The 1st-3rd ones take part in the development of the facial skull
gill arches (Fig. 12). The gill pouch between the 1st and 2nd gill arches in humans differentiates into the middle ear cavity and the auditory tube.
Rice. 12. Initial stage of facial development; embryo 5-6 weeks:
a - side view: 1 - frontal tubercle; 2 - eye rudiment; 3 - mandibular (1st) gill arch; 4 - auditory vesicle; 5 - 2nd (hyoid) gill arch; 6 - 3rd and 4th gill arches; 7 - first gill pouch; 8 - cardiac protrusion; 9 - mouth bay;
b - front view: 1 - frontal tubercle; 2 - medial nasal process; 3 - lateral nasal process; 4 - maxillary process of the 1st branchial arch; 5 - mandibular process of the 1st branchial arch; 6 - mouth bay; 7 - 3rd and 4th gill arches; 8 - 2nd gill arch; 9 - 1st gill pouch; 10 - nasolacrimal groove; 11 - eye rudiment; 12 - olfactory fossa.
The mandibular gill arch on each side forms 2 processes - maxillary and mandibular, which limit the oral bay from below and from the sides. Between the maxillary processes there is a frontal process, which, during the formation of the olfactory fossae, is divided into 5 parts: the unpaired frontal process and the paired lateral imedial nasal processes. The medial nasal process forms the vomer, the perpendicular plate of the ethmoid bone, and the premaxillary bone (usually existing as a separate bone before birth). The lateral nasal process is the source of the formation of the labyrinth of the ethmoid bone, nasal and lacrimal bones. The maxillary and lateral nasal processes limit the orbital cavity,
which continues downward and medially into the nasolacrimal groove, connecting to the olfactory fossa. Subsequently, the nasolacrimal groove closes, forming a nasolacrimal canal on each side (Fig. 13). From the maxillary process the upper jaw (with the exception of the area corresponding to the incisors), palatine and zygomatic bones, and the medial plate of the pterygoid process of the sphenoid bone develop. The palatine processes extend from the medial surfaces of the maxillary processes. Οʜᴎ connect with each other and with the septum of the nasal cavity, forming the palate (Fig. 14).
Rice. 13. Further stages of facial formation in embryogenesis:
a - 7 weeks of embryonic development, front view; b - the same, right view;
c - 8 weeks of embryonic development, front view; d - the same, right view
Rice. 14. Development of the palate, ventral view:
a - 6-7th week: 1 - frontal tubercle;
2 - medial nasal process; 3 - lateral nasal process; 4 - nasolacrimal groove; 5 - maxillary process of the mandibular branchial arch; 6 - palatine process of the maxillary process; 7 - base of the skull - roof of the oral bay; 8 - growing septum of the nasal cavity; b - 7-8th week: 1 - filtrum - place of fusion of the medial nasal processes; 2 - place of fusion of the medial nasal and maxillary processes;
3 - primary palate; 4 - primary choanae; 5 - palatine processes of the maxillary processes; 6 - growing septum of the nasal cavity;
c - 8-10th week: 1 - upper lip; 2 - gums; 3 - secondary palate
From the mandibular process, the lower jaw develops periosteally (Fig. 15). The 1st branchial arch also gives rise to the malleus and incus, the 2nd branchial arch gives rise to the stapes, the styloid process of the temporal bone, the lesser horns of the hyoid bone, the 3rd branchial arch gives rise to the body and greater horns of the hyoid bone (see Fig. 15).
Rice. 15. Development of the lower jaw, auditory ossicles and laryngeal cartilage:
1 - hammer; 2 - anvil; 3 - stirrup; 4 - styloid process of the temporal bone; 5 - stylomandibular ligament; 6 - large horns of the hyoid bone; 7 - thyroid cartilage of the larynx; 8 - arytenoid cartilages of the larynx; 9 - cricoid cartilage of the larynx; 10 - small horns of the hyoid bone;
11 - chin bone; 12 - lower jaw
The individual ossifications from which the bones of the skull develop continue to fuse with each other only after birth.
Particularly significant are the remains of the connective tissue membranous skull in the walls of the brain skull where several bones meet. Here, the newborn’s soft areas of the skull are felt, which are called fontanelles. There are six of them: two unpaired and two paired on each side.
The largest - front– a diamond-shaped fontanel; otherwise it is called a large fontanel. It is located where the right and left halves of the frontal bone and the right and left parietal bones meet. Another unpaired one - ask- the fontanelle is placed where the right and maiden parietal bones and the occipital bone meet.
On the left and right sides there are lateral paired fontanelles. The front one is wedge-shaped- is located where the frontal, parietal bones and the greater wing of the sphenoid bone meet. Posterior lateral (or mastoid) the fontanel is located in the place where the occipital, parietal bones and the mastoid process of the temporal bone converge.
After birth, as a result of the growth of the edges of the cranial bones, cranial sutures are formed: in the area of the facial skull - smooth with smooth edges, in the area of the brain skull - jagged, between the temporal and parietal bones - a scaly suture. When sutures are formed between the smooth, jagged and scaly edges of the cranial bones, fibrous connective tissue containing bone-forming elements is preserved. The main role of the cranial sutures is that bone growth occurs here along the edges.
Simultaneously with the formation of sutures, ĸᴏᴛᴏᴩᴏᴇ ends in the 3-5th year of life, the fontanelles close. In this case, the angles of the parietal bone are formed. Earlier than others, in the 2nd month of life, the mastoid fontanel closes. Later - only by the age of 3 - the wedge-shaped fontanelle finally closes. The anterior fontanel, which closes by the age of 1.5 years, is of greatest practical importance. It is this fontanel that is for pediatricians an indicator of the progress of ossification of the skull and skeleton as a whole. Non-closure of the anterior fontanel after 1.5 - 2 years of life indicates a delay in ossification of the skull, and therefore the entire skeleton.
Not only in structure, but also in shape, the skull of a newborn differs from the skull of an adult. The proportions and ratio of the cerebral and facial skulls in an adult and a newborn are different. The newborn has a relatively large brain and a relatively small facial skull. In an adult, the facial skull is relatively larger. In terms of mass and volume, the brain is 8 times larger in a newborn than the facial, in an adult - only 2 times.
However, in intrauterine life the cerebral skull grows more intensively than the facial skull; after birth the reverse situation is observed. This is explained by the fact that the growth and formation of the brain skull are determined first and foremost by the growth and development of the brain. In higher mammals and humans, brain development already in the early stages is characterized by progressive growth of the anterior region. Active growth of the brain also determines the progressive growth of the cerebral skull in comparison with the facial skull.
In a newborn, the upper part of the facial skull is most developed, since during the prenatal period the eyeball grows very vigorously. The eyeball is a derivative of the brain. The lower part of the facial skull in uterine life lags behind in growth, since its formation is associated with the respiratory and chewing functions, which, naturally, have a formative influence only after birth. These functions come into effect only after birth. Naturally, the facial skull grows and forms mainly after birth.
If we return from the individual development of the skull in humans to the evolution of the skull in vertebrates, it should be noted that in the course of evolution the cerebral skull recedes into the background. In amphibians, the facial skull is located directly anterior to the cranium. The facial and cerebral skulls occupy the same position relative to each other in most mammals. Only in higher mammals does the facial skull seem to retreat back and move under the brain skull. This can be seen on the skull of a baboon and even better on the skull of great apes (chimpanzees, gorillas).
In modern humans, the brain skull is 2 times larger than the facial skull.
During the prenatal period, the cerebral skull grows more rapidly than the facial skull, and, in addition, has a relatively larger size than the skull of an adult. After birth, the brain skull lags behind the facial skull in growth. The facial skull, which in a newborn is, so to speak, hidden under the brain skull, protrudes anteriorly after birth - prognathism increases. The facial angle decreases after birth. This shows that in the ontogenesis of the skull, which generally repeats evolution, the course of development shifts in time based on the formative influences that the function has on the developing organism and its individual parts. Since the respiratory and chewing functions are not realized in uterine life, the facial skull in this period lags behind in growth. When these functions come into play after birth, the facial skull is ahead of the brain skull in development. This leads to a change in the proportions of the skull in the postnatal period. Thus, ontogeny does not blindly repeat phylogeny. Development is determined by the conditions of existence of the organism, the functions of organs, and the entire organism of the embryo or growing animal as a whole.
After birth, growth occurs unevenly not only in the area of the facial and cerebral skull, but also in different parts of the cerebral and facial skull, as well as over time.
Three periods of skull growth can be distinguished: 1) a period of vigorous active growth - from birth to 7 years, 2) a period of slow growth - from 7 years to puberty, i.e. 14-16 years, 3) a new period of active growth of the skull - from the age of puberty to 25-26 years, when the growth of the entire skeleton ends.
The first period of vigorous growth of the skull is in turn divided into three segments. During the 1st year of life, the skull grows more or less evenly in all directions. From 1 to 3 years, the skull grows especially actively at the back. The occipital part of the skull is formed; at the 2nd - 3rd year of life, the back of the head becomes convex. At the same time, that part of the skull that is located posterior to the foramen magnum increases, and the foramen itself changes its position. If in a newborn the foramen magnum is located in the transverse plane of the body, then in the 2nd - 3rd year of life it seems to be open downward and forward and is located obliquely, as if open downward and forward, its anterior edge becomes higher than the posterior one.
The strong growth of the occipital part of the skull and a change in the position of the foramen magnum are associated with the child’s transition to upright posture in the 2nd year of life. To a certain extent, this repeats the course of evolution of the skull. In four-legged mammals, the head is suspended from the vertebral column in front and is supported by powerful occipital muscles and ligaments: the foramen magnum is directed posteriorly. In primates, due to the fact that they lead an arboreal lifestyle and sometimes assume a vertical position, the skull begins to take a new position in order to maintain balance. Simultaneously, in monkeys, with an increase in the relative size of the brain skull, the foramen magnum rotates downward and gradually becomes established, as seen in anthropomorphic monkeys (chimpanzees, gorillas), obliquely, openly downward and posteriorly. The continuation of this process of formation of the occipital part of the skull and the movement of the foramen magnum to the lower surface of the skull occurred in human ancestors, in particular in Pithecanthropus. In an upright person, the skull balances in balance at the upper end of the spinal column and the foramen magnum is located so that it is open not only downwards, but also anteriorly. Changes in the phylogeny of the location of the foramen magnum seem to be repeated in individual human development.
In the 2nd - 3rd year of life, due to the eruption of baby teeth, the growth of the facial skull in height and width significantly increases, which also affects the development of the initial part of the respiratory tract, i.e., the nasal cavity. At this age, the parietal bones actively grow. The crown, which is flat in a newborn, becomes convex; from the end of the 3rd year, sutures will form.
During the third segment of the first period of skull growth - from 3 to 7 years - the growth of the entire skull continues with particularly active growth of its base. By the age of 7, the growth of the base of the skull in length is basically complete. The base of the skull reaches almost the same size as that of an adult.
In the second period of skull development - from 7 years to puberty (14 - 16 years) - skull growth slows down; It is mainly the cranial vault that grows.
In the third period - from puberty to 25-26 years - the frontal section of the brain skull expands and deepens, and the facial skull also actively grows. During this period, sexual characteristics of the skull appear: in boys, the facial skull grows in length more than in girls; the face lengthens. If before puberty boys and girls have rounded faces, then after puberty in women the face retains its characteristic roundness, while in men, as a rule, it becomes elongated.
There is a large literature on the issue of differences between male and female skulls. A number of features have been put forward that distinguish male and female skulls. Today it is generally accepted that the characteristics of the male and female skulls consist, firstly, in gender differences in the size of the skull: the male skull, due to the large overall size of the body, is larger than the female one. The capacity of the skull in men is 1559 cubic meters. cm, for women 1347 cc. see, ᴛ.ᴇ. on average for men 212 cc. cm more than women. Moreover, if we calculate the relative capacity of the skull per 1 cm of body length, it turns out that in women it is larger; than men.
If we compare the development of the cerebral and facial skulls, it turns out that the cerebral skull is relatively highly developed in women, and the facial skull is more developed in men. The female skull seems to retain to a greater extent the features of the children's skull of our ancestors. For women, a smaller protrusion anterior to the facial skull is typical; the female skull is less prognathic than the male one. This is related to the features of the profile line of the male and female skull. In men, the facial skull protrudes relatively more forward; the profile line of the forehead, rising gently upward, passes into the convex crown and continues with the convex line of the back of the head. In women, the facial skull protrudes slightly anteriorly, and therefore the profile line of the forehead is directed vertically upward. It, bending sharply, passes into the flat line of the crown, and the latter, with a sharp bend, into the profile line of the flattened nape falling down. As a rule, the male skull is distinguished by a more pronounced relief of muscle attachments; in women, the relief of the skull is less pronounced.
So, the growth of the skull after birth continues unevenly in its individual parts and in certain periods of postnatal life. Starting from the period of puberty, the sexual characteristics of the formation of the skull are determined. What are the mechanisms of skull growth?
The bones of the skull, like the entire skeleton, grow through apposition, i.e., the application of new layers of bone plates to an existing bone. Cranial bones grow through the apposition of new bone substance to the surface of the bones, as well as at cranial sutures and synchodrosis. Naturally, after the growth of the cranial bones ends, the function of the cranial sutures ceases and they close, that is, they become overgrown with bone tissue. It starts at 25 - 40, most often at 30 years old.
The sutures of the skull are overgrown with bone tissue in a certain sequence. First, the cranial sutures close from the inside of the cranial cavity, i.e., the internal compact plates of bones grow together, and later the sutures close from the outside. At the age of 22 - 35 years, the sagittal suture closes, at 24 - 38 years - the coronal suture in the middle part, at 26 - 41 years - in its lower part, at 26 - 42 years the lambdoid suture. Later than others, the mastoid-occipital (from 30 years old) and scaly (from 37 years old) sutures are closed.
The time and order of fusion of cranial sutures are individually variable. If intracranial pressure is increased for one reason or another, the healing of sutures is delayed until old age. Thus, it is known that the famous philosopher of the second half of the 18th century, Kant, had cranial sutures that did not heal until he was 80 years old.
If we compare, for example, the lower jaw of a newborn and an adult, it becomes clear that if the lower jaw grew only by uniformly applying bone substance over its entire surface, then the jaw of an adult could never emerge from the jaw of a newborn. During the process of growth, the cranial bones, like other skeletal bones, not only increase in size, but also change shape. On the other hand, comparing the skulls of a newborn and an adult, one can notice that the skull of a newborn fits freely into the cranial cavity of an adult. If the growth of the skull consisted only in the fact that new bone substance was superimposed on its bones, then the cranial cavity could not increase. Measuring the shape of bones and enlarging the cranial cavity is possible only because during the growth of the skull, on the one hand, new bone substance is applied by apposition, and on the other hand, previously formed bone tissue is destroyed. During the growth of the skull, contradictory processes of new formation and destruction of bone tissue are intertwined.
Microscopic studies show that, for example, the parietal bone grows in such a way that on its outer surface and along its edges in the sutures, osteoblasts form ever new rows of bone plates, and on the inner surface of the bone, osteoclasts destroy bone tissue. A microscopic examination of the growing lower jaw revealed that simultaneously with the application of new bone substance along the posterior edge of the jaw ramus, the bone substance is destroyed at the anterior edge of the lower jaw ramus. Using the example of the lower jaw, you can see how the shape of the bone changes as the skull grows. In the fetus, the body and branch of the lower jaw are on the same straight line, i.e. they form an angle of 180 degrees. In a newborn, they are also located almost in one straight line and form an angle of 150°. The structure of the lower jaw is such that most of the bone body is occupied by bone cells in which the dental sacs are located, but there are no alveoli or sockets yet. Only when teeth erupt does the alveolar process form and the alveolar margin is formed. Taking into account the dependence of the action of the masticatory muscles on the lower jaw, the body of the lower jaw grows and becomes taller. In connection with the eruption of teeth and changes in the relationship between the upper and lower jaws, the mechanical conditions of movement in the mandibular joint, the direction of the bundles of masticatory muscles and the traction of the masticatory muscles change. In this regard, the angle between the body and the ramus of the lower jaw decreases and in an adult it ranges from 120 to 130°.
In old age, the shape of the lower jaw changes again. After teeth fall out, the alveolar process resolves and only a narrow arch of the body of the lower jaw remains. The chewing function gradually fades away and the muscles weaken. With the weakening of muscle traction, their formative influence on the bone is lost.
Taking into account the dependence of teeth falling out, disruption of the relationship between the upper and lower jaws, and changes in the masticatory muscles, the shape of the lower jaw changes again. The angle between the body and the arch of the lower jaw increases again and reaches 140°. The lower jaw seems to return to the shape characteristic of a newborn. But this impression is erroneous; the similarity in the shape of the lower jaw of a child and an old man is purely external. In a newborn, the entire lower jaw is filled with dental sacs, and in old people, the alveolar process completely disappears and only a narrow arch of the jaw body remains.
Senile changes are found not only in the lower jaw, but throughout the entire skull. Due to the fact that the muscles weaken, the relief of the skull is smoothed out, the bumps and roughness resolve. The skull becomes lighter. Partial resorption of the spongy substance occurs, especially of the flat cranial bones. The crown is somewhat flattened, as the outer and inner plates of the compact substance of the parietal bones come closer together. At the same time, the elasticity of the skull decreases and it becomes fragile. In an adult, the skull is elastic; when compressed in the transverse direction, its width can decrease by 1 cm. Old anatomists performed the following experiment in front of an audience of students: they threw the skull of a young man onto a stone floor, and it, having elasticity, bounced like a ball; then they threw the old man's skull, and it crumbled into pieces.
So, throughout a person’s entire life (in the uterine period and after birth until old age), the shape and structure, strength and elasticity of the skull continuously change. The continuous change in the shape and structure of the skull is determined by the continuous change in its functions as support and protection for the soft parts of the head and face.
The brain plays a primary role in the development of the skull and its formation. Progressive development of the brain during the evolution of vertebrates causes changes in the ossification of the brain skull. In human ontogenesis, the early progressive development of the brain skull depends on the development of the brain in the early stages of uterine life. The influence of the brain on the formation of the skull determines many features of the relief of the inner surface of the cranium. For scoliosis, ᴛ.ᴇ. lateral curvatures of the spinal column, the right and left halves of the base of the skull bear an unequal load. On the side of the curvature of the spinal column, the imprints of the cerebral convolutions are deeper. This natural experiment reinforces the view that brain formation plays a decisive role in the growth and development of the skull.
Other organs and soft tissues of the head (eyeball, masticatory muscles, glands, contents of the nasal cavity, etc.) also affect the shape of the skull. Numerous experiments, in particular those conducted at the end of the last century by the famous Russian anatomist P. F. Lesgaft and his students, show that the growth and shape of the skull is determined by the influence of the soft parts of the head and face. The experimenters removed the eyeball and the entire contents of the orbit from young puppies. The puppies grew up, they were killed and the shape of the skull of the operated puppies was compared with the shape of the skull of the control puppies - normally growing puppies of the same litter. After removal of the contents of the orbit, the latter on the operated side decreased in size, and the shape of the bones involved in its construction changed. Moreover, the shape of the entire brain skull also changed: the corresponding half of the cranial cavity increased based on the preferential growth of the cerebral hemispheres in the direction of least resistance, i.e., on the side where the contents of the orbit were removed. The skull became asymmetrical. In the same way, the shape of the facial skull and the entire configuration of the head in puppies change after removal of the nasal turbinates. After such an operation, the shape of the skull of the puppies of a pointing dog changed so much that it began to resemble the skull characteristic of dogs of another breed - pugs.
The formation of the skull is greatly influenced by the muscles of mastication. Removal of the temporal muscle causes the development of asymmetry of the brain and facial skull.
The role of mechanical influences on the formation of the skull was studied by P.F. Lesgaft and his students. Οʜᴎ bandaged the skulls of puppies in different directions and obtained different shapes of the skull, incl. boat-shaped and tower.
The influence of the mechanical factor on the development of the skull is also proven by observations of people. In the middle of the last century, travelers noticed that some Indian tribes in the territory of modern Mexico believed that a man, in order to be a good hunter and winner in battles, must have a high, tower-shaped skull. In order to make their son a good hunter and warrior, the parents took measures to develop the tower shape of the skull. Already in infancy, the boy's head was placed not on a pillow, but on a log, which was placed under the back of the child's head. The skull only grew upward. Holding the child in her lap, the mother placed her hand on his forehead and held it so that it pressed on the skull.
In the vicinity of Toulouse (France), in the last centuries, a girl with a head stretched to the back of her head was considered beautiful. Parents bandaged the girls' heads in a transverse direction, thereby achieving the desired shape of the skull - the so-called Toulouse head. The back of the head stretched up and back: this was emphasized by a special hairstyle. This head shape was considered beautiful in this area.
The variety of internal and external factors that influence the growth and formation of the skull make it clear that the shape and size of the skull have very large individual differences. Individual differences in skull shape are studied by a special branch of anthropology called craniology. This science uses a method of direct observation of the skull - cranioscopy and a method of measuring the skull - craniometry. The skull is examined from above - in the vertical norm, from below - in the basilar norm, from the side - in the lateral norm, from behind - in the occipital norm and in the sagittal section, i.e. in the median norm. The contour of the skull in different norms determines individual differences in the shape of the brain and facial skull. For example, in the vertical norm, a rhomboid, spheroid, pentagonoid, etc. skull is distinguished by comparing the outlines of the skull with various figures. The average and extreme variants of the absolute value of certain dimensions of the skull are determined craniometrically. For example, it is known that on average, Russians inhabiting the middle zone of the European part of Russia have a maximum skull length of 175 mm, width of 142 mm, height of 133 mm.
Moreover, the shape of the skull is characterized not only by absolute sizes in different directions, but also, most importantly, by the ratio of these sizes. These relationships are expressed in numerous pointers or indices. The most common is the cephalic index. It represents the greatest width of the cranium, expressed as a percentage of the length. This index characterizes the ratio of the length and diameter of the skull. If the length of the skull is taken as 100, and the width is expressed as a percentage of the length, you get a relative number characterizing the shape of the skull. An index from 75 to 80 indicates the average value of the index - a medium-headed, mesocephalic skull, less than 75 - a long-headed, dolichocephalic skull, and more than 80 - a brachycephalic, short-headed skull. The cephalic index is one of the signs of physique, which together make it possible to distinguish between human races within humanity as a collective species.
For decades, fascist anthropologists sought to prove the superiority of the North Germanic - dolichocephalic race over the Slavic - brachycephalic (average cephalic index of the Slavic race is 81). They believed that the highest race was North Germanic, or Nordic. It was proven that only this race, characterized by a dolichocephalic skull, possesses the characteristics of the higher structure of the skull. Some English and American scientists preached the superiority of the Anglo-Saxon race over others. At the same time, anthropological studies show that this or that skull shape does not belong to any one race. A greater degree of long-headedness than in the North Germanic race is found among the Negroes. On the other hand, the head indicator varies over a significant period within one population. In all races of modern humanity, gradual brachycephalization occurs, the cephalic index changes towards brachycephaly (round-headedness). The shape of the head also changes based on the living conditions of the same person over a relatively short time. Using the example of immigrants from Italy and Poland to America, American anthropologists showed that the cephalic index changes under the influence of the external environment.
If blacks have a nose shape that is more similar to the shape of the nose of human ancestors, then the shape of their lips is more differentiated than that of Europeans. The white race retained more developed skin hair. Racial characteristics, incl. head index, have no adaptive significance.
However, it is wrong, when comparing the structure of the human skull with the structure of the skull of apes and other primates, to draw a conclusion about the higher or lower position of individual races on the ladder of evolution. Humanity is represented by one species - Homo sapiens.
Finally, it is completely unscientific to connect certain features of the shape of the head or different sizes of the capacity of the skull, or even different masses of the brain with the degree of development of higher nervous activity.
How great are individual differences in the shape and structure of the skull, how significant is the variability in the structure and shape of the skull, how untenable are attempts to connect intellectual development with the shape of the skull, is evidenced by the fact that even each individual person has
DEVELOPMENT OF THE SKULL - concept and types. Classification and features of the category "SKULL DEVELOPMENT" 2017, 2018.
