The human body in different periods of life has different proportions. The head, trunk, arms and legs are in constant proportions for each age. Of course, there are individual fluctuations (depending on gender, race, etc.), but the limits of these fluctuations are relatively small, so people of the same age, on average, have the same proportions of the body. And if this proportionality is violated, then it is perceived by us as a violation of harmony or an aesthetic flaw.
According to the general canons, in a properly folded human body, the length of the head is 8 times smaller than the length of the whole body and 3 times smaller than the length of the trunk. The length of the arms is 3.25, and the leg length is 4.25. The body of the child has completely different proportions. Thus, in a newborn the length of the head is only 4 times smaller than the length of its body, the length of the arms is 1.6, and the length of the legs is 2.5 times the length of the head. By the year these ratios are changing. The length of the head fits in the body length about 5 times, and the length of the arms is equal to the length of the legs. Thus, the child (in comparison with the adult) is a short-legged and short-armed creature with a large head and large eyes. (The eyes during the growth of a person - from childhood to adulthood - grow much slower than other parts of the body.) Therefore, the eyes are much larger in relation to the proportions of the head in children than in adults.)
This phenomenon is used by artists-animators. If they want their character to evoke tenderness, love and other pleasant emotions, then they portray him with the proportions of the child - a big head, huge eyes with long eyelashes, short paws (or pens and legs). And vice versa - an evil character is necessarily drawn in the proportions of an adult.
From proportions we pass to absolute values. After the child turns a year, the pace of his physical development is somewhat slowed down. The weight of his body increases on average only 30-50 g per week.
In a child at the age of one year, the head circumference reaches an average of 46.6 cm, by a year and a half it increases to 48 cm, and in two-year-olds to 49 cm. Thus, in the second year of life, the head circumference increases by 2 cm. Whether the child develops correctly, along with the mass and length of the body determine its proportionality. For example, it is believed that the child's circumference of the breast is greater than the circumference of the head by as many centimeters as the child's age.
The legs grow much longer than the arms. While the newborn's arms are somewhat longer than the legs, by the year the limbs become the same length, and the two-year-old has legs longer than the arms. Consider the skull of a child. It is divided into the facial and brain parts. The cerebral part of the skull is much larger than the cerebral part, especially in newborns. With age, the entire skull grows, but its facial part grows much faster than the brain. Especially important for the appearance is the growth of the lower jaw. This bone consists of the bony arch and branches that branch out from it. The angle formed by the branches and the arc varies with age) from the blunt to the straight. In women, the shape of the lower jaw (like the whole skull as a whole) in the adult state is very similar to that of the baby.
The weight of the child's body changes. During this period, it increases by about 200-250 g per month, which is about 2.5-3 kg per year. And the growth increases by 12 cm, and with each month it slows down. Sometimes it can even stop and stay unchanged for 1-3 months. This may depend on nutrition, the environment and other factors. However, both growth and body weight are more dependent on heredity.
Between the year and 18 months, as a rule, there are four premolars. And between the 16th and 24th months fangs erupt. The order of teething may be impaired, but on average, by the 25th month of life, the baby should have 20 milk teeth.
Sometimes teething may be accompanied by local pain, drooling, irritability, decreased appetite.
Despite the fact that a child at the age of one to one and a half years is already well worth and walks, the structure of his body does not yet fully correspond to the function of the erect, distinguishing man from higher animals.
The fact is that the feet of his short legs are still very small, and the head is big and heavy. The muscles of the neck, back, legs are not yet strong. All this makes it difficult to maintain balance. In addition, the child's vestibular apparatus is still insufficiently developed.
The spine of an adult man has several physiological curves that facilitate standing and walking. These bends are called lordosis and kyphosis. Lordosis is a bend anteriorly. Kyphosis - back. The adult has cervical lordosis, thoracic kyphosis, lumbar lordosis and sacrococcygeal kyphosis. Physiological bends serve as a kind of shock absorbers, softening the shaking of the body when walking, running and jumping.
In children, especially small children, the spine does not have all of these bends. In addition, he is not yet strong, his ligamentous apparatus is not fully formed and begins to ossify only towards the end of preschool age. And the bends of the spine are formed and fixed to an average of 13-15 years. And the formation of them is consistent. In a newborn, the spine has the shape of an almost straight post. When the baby starts to hold his head and neck muscles are turned on, cervical lordosis begins to form. Later, when the child starts to sit, there is a thoracic kyphosis. And after the child starts to stand and walk, the lumbar lordosis forms. But even at this time, when the child lies down, his spine straightens again, because he has not yet reached the necessary degree of ossification.
In general, the bones of a child reach full maturity only to the period of puberty. Until then, the superficial layer of the child's bone - the periosteum - is much thicker than in adults. Therefore, children often have fractures like "green twigs". Have you ever broken green young shoots of shrubs? Remember how it happened: inside the stem broke, and outside the thick juicy peel keeps it and is almost not broken. Such are the subperiosteal fractures in children. In addition, the bones of the hand and foot still have a cartilaginous base and ossify at a certain time.
Cardiovascular, respiratory and digestive systems for these six months (from year to year and a half) do not undergo any noticeable changes. Thus, the heart rate remains at about 120 per minute, the respiratory rate is at least 30 breaths per minute. As for the gastrointestinal tract, it continues to work the same way unless, of course, you have introduced a shish kebab, barbecue, lard with garlic and other meat products not provided for this age in the child's diet.
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