Animals. As we know, the origin of the class of mammals is closely related to ancient reptiles; evidence of this was the fossil remains of beast-toothed lizards. Over a long period of time, mammals developed, and the structure of their bodies, organs, and brain improved, and they acquired new abilities they needed to survive.

The main features of modern mammals are hair, mammary glands, and warm-bloodedness, which played an important role in the struggle for survival and a new way of developing offspring - bearing children in the womb. Therefore, mammals have taken a dominant position in the world.

The class mammals includes a huge number of animals, total number which exceeds 4.5 thousand. By appearance All mammals differ from each other, but in terms of internal structure, almost all representatives are the same, as a result, two subclasses of mammals are distinguished:

Primordial subclass– this group includes primitive vertebrates, their structure is very similar to reptiles, for example, the ability to lay eggs and the presence of coracoid bones remain, while in real mammals, this bone is presented in the form of a regular outgrowth. There are about 40 species of these animals.

Subclass real animals– this group includes the bulk of mammals inhabiting our planet, which are divided into two infraclasses: lower and higher animals.

External structure of mammals. The body of all mammals can be divided into four sections: the head, the torso, two pairs of limbs and the tail, and the first pair of limbs may be underdeveloped. The head consists of the upper and lower jaws, eye and ear sockets, as well as at the front end of the muzzle, slit-like nostrils. The eyes have an upper and lower eyelid, with cilia located on their edges. Most mammals have special hair or whiskers that serve as a sense of touch. The olfactory nerves are developed in the nasal cavity. There are fingers at the end of the front and back pairs of limbs. At the bottom of the body, there are nipples that open the ducts to the mammary glands.

Cover of mammals

The entire body of mammals is covered with dense hair. In some representatives on certain parts of the body, instead of hairline, formed horny scales, mainly characteristic of reptiles and fish. All mammals have varied hair and can be in the form of long or short hair, rough, thick, fluffy, soft, hard, etc. Just like birds, mammals are capable of molting, shedding old hair and gradually replacing it with new, thicker hair. Hair consists of a horny substance that is deepened into the skin of the animal. The recess is called the hair follicle, at the base of which the hair follicle is located. To prevent hair from drying out, it is lubricated with fat secreted by the sebaceous glands.

Internal structure of mammals. The entire body of these animals is covered with a layer of muscles. The muscles of mammals are very well developed, as a result they become agile, fast, sharp animals. For all mammals, the typical muscle is the diaphragm, presented in the form of a muscular partition between the thoracic and abdominal cavities of the body.

Skeleton of mammals

Typically the skeleton consists of the skull, spinal column, pelvic girdle, femur, chest, legs, feet, hands, forearm, humerus and shoulder blades. Unlike birds, the bones of mammals are not hollow inside, but filled with a special fatty substance (bone marrow). Also in mammals, the cranial bones are connected to each other using sutures, and not, like in birds, fused. The skull is connected to the spinal column thanks to two articulated processes. The spinal column can be divided into five sections: cervical, thoracic, lumbar, sacral and caudal. The number of vertebrae is different for all representatives of this class. The breastbone and ribs, which form the rib cage, are connected to thoracic vertebrae. The sacral vertebrae, which have a triangular shape, are connected to the bones of the pelvic girdle. The mammalian limb skeleton mainly consists of three parts: the foot, leg and thigh.

It would seem that the question is not at all difficult and we all covered this topic at the beginning of studying biology in school years. However, most adults cannot immediately answer this question. In this article we will look at both types in detail and compare them, so that after reading you will never be able to confuse how animals differ from mammals!

What do we know about animals?

First, let's try to define each of these concepts and then draw a parallel. So, animals are a classically distinguished fraction of living organisms, part of the biological kingdom. All animals, without exception, are studied by zoologists and divided into categories, types and subtypes. They are eukaryotes, which means that their cells have nuclei. They can move actively, are divided into wild and domestic, and much more.

Modern classifications of the animal world

Modern zoologists put forward many theories on the classification and typification of animals. The most famous of them are divided into:

• Types.
• Classes.
• Squads.
• Families.
• Childbirth.
• Kinds.

Unfortunately, within the framework of this article we will not comprehensively cover this topic. After all, our goal is to find out what the difference is between animals and mammals, and not to delve into zoology. To understand the topic, we need to consider in detail only the classes of animals, which include mammals. That is, looking ahead, it becomes clear what the main difference between these two concepts is.

The difference between animals and mammals is that the second concept is narrower and is included in the first. But for complete understanding, let's deal with everything in order.

There are only eight units in the animal classes. This:

1. Crustaceans.
2. Arachnids.
3. Insects.
4. Birds.
5. Reptiles.
6. Amphibians.
7. Fish.

What are mammals?

So we get to the second definition, what are mammals?

As we have already found out, mammals are a separate class of animals. All mammals, without exception, are vertebrates. The main one distinctive feature(as you can already guess from the name) - they feed their young with milk. As you might guess, not all animals can do this (for example, fish or insects, everyone knows, do not do this). Moreover, they are all quadrupeds. Knowing these basics, it is not difficult to learn to distinguish mammals from other animals.

But as far as external data is concerned, mammals are a very diverse class. Representatives of the class of mammals are moles, hedgehogs, squirrels, beavers, mice, wolves, foxes, bears, seals, walruses, whales, dolphins, giraffes, elephants and all domestic animals (goats, cows). They are also divided into subclasses. Their features are hair, skin glands, constant body temperature, warm-bloodedness, viviparity, looking after offspring, and complexity of behavior. In general, they are all easily distinguished from other representatives of the fauna world.

Let's sum it up

Now that we have familiarized ourselves in detail with each of the terms presented and learned (or, rather, remembered) about each of them, it’s time to answer the basic questions of this article. How do animals differ from mammals?

1. As it turns out, mammals are those who feed their young with milk. Other animals don't do this. If you ever forget about it, the name of this class will always tell you. In order to feed the baby, female mammals have mammary glands.
2. They are viviparous - that is, before birth, the fetus develops inside the female (many animals, for example, lay eggs), this is another difference from other animals.
3. Some individuals can fly. These are, for example, bats or flying dogs (this happens too!). While other animals, with the exception of the class of birds, crawl or swim.
4. They take care of their offspring (unlike many other representatives of the animal world). Cubs after birth for a long time, and sometimes all their lives, are with their flocks. They are taught to hunt, get food, and even play with them.
5. All of them are four-legged (as opposed to reptiles, fish, birds and other animals).

Here are the main differences inherent in the class of mammals. In this article, we answered the question of how animals differ from mammals, identified them as a separate class and provided basic concepts on the topic. Now you can easily distinguish a mammal from another animal or explain to your child what is the difference between them.

Animals or mammals are the most highly organized. A developed nervous system, feeding their young with milk, viviparity, and warm-blooding allowed them to spread widely throughout the planet and occupy a wide variety of habitats. Mammals are animals that live in forests (wild boars, moose, hares, foxes, wolves), mountains (rams, steppes and semi-deserts (jerboas, hamsters, ground squirrels, saigas), soil (mole rats and moles), oceans and seas ( dolphins, whales). Some of them (for example, bats) spend a significant part of their active life in the air. Today, the existence of more than 4 thousand species of animals is known. Orders of mammals, as well as characteristics, inherent in animals - we will talk about all this in this article. Let's start with a description of their structure.

External structure

The body of these animals is covered with hair (even whales have its remains). There are coarse straight hairs (hair) and fine curly hairs (undercoat). The undercoat protects the hair from contamination and matting. The coat of mammals can consist only of awns (for example, in deer) or from undercoat (as in moles). These animals shed periodically. In mammals, this changes the thickness of the fur, and sometimes the color. The skin of animals contains hair follicles, sweat and sebaceous glands and their modifications (mammary and odorous glands), horny scales (as on the tail of beavers and rats), as well as other horny formations found on the skin (horns, hooves, nails, claws). Considering the structure of mammals, we note that their legs are located under the body and provide these animals with more advanced movement.

Skeleton

They have a highly developed braincase in their skull. In mammals, teeth are located in the cells of the jaws. They are usually divided into molars, canines and incisors. The cervical spine in almost all animals consists of seven vertebrae. They are movably connected to each other, except for the sacral and two caudal ones, which, fused, form the sacrum - a single bone. The ribs articulate with the thoracic vertebrae, which are usually from 12 to 15. In most mammals, the girdle of the forelimbs is formed by paired shoulder blades and clavicles. Only a small part of the animals have crow bones preserved. The pelvis consists of two pelvic bones fused to the sacrum. The skeleton of the limbs is made of the same bones and sections as those of other representatives of four-legged vertebrates.

What sense organs do mammals have?

Mammals are animals that have ears that help them detect odors and also determine their direction. Their eyes have eyelids and eyelashes. On the limbs, belly, and head there are vibrissae - long, coarse hairs. With their help, animals sense even the slightest touch of objects.

Origin of mammals

Just like birds, mammals are descendants of ancient reptiles. This is evidenced by the similarity of modern animals with modern reptiles. It is especially evident in the early stages of embryonic development. An even greater number of similarities were found in them with wild-toothed lizards, which became extinct many years ago. Also, the relationship with reptiles is evidenced by the fact that there are animals that lay eggs containing many nutrients. Some of these animals have cloaca, developed crow bones and other signs indicating low organization. It's about about the primal beasts (oviparous). Let's tell you more about them.

Primordial beasts

This is a subclass of the most primitive mammals alive today. Along with the signs already mentioned, it should be noted that they do not have a constant body temperature. The mammary glands of primal beasts do not have nipples. The cubs, hatched from the eggs, lick the milk from the mother's fur.

In this subclass, one order is distinguished - Monotremes. It includes 2 species: the echidna and the platypus. These animals can today be found in Australia, as well as on the islands adjacent to it. The platypus is a medium-sized animal. It prefers to settle along the banks of rivers and leads a semi-aquatic lifestyle here. He spends most of his time in a hole he dug in a steep bank. In the spring, the female platypus lays eggs (usually two of them) in a special burrow equipped with a nesting chamber. Echidnas are burrowing animals. Their body is covered with hard hair and spines. The females of these animals lay one egg, which they place in a pouch, a fold of skin located on the abdomen. The baby hatched from it remains in the pouch until needles appear on its body.

Marsupials

The order Marsupials includes animals that give birth to immature cubs, after which they carry them to term in a special pouch. Their placenta is poorly developed or does not form at all. Marsupials are distributed mainly in Australia, as well as on the islands adjacent to it. The most famous of them are the marsupial and the giant kangaroo.

Insectivores

Insectivores are an order that unites ancient placental primitive animals: hedgehogs, shrews, moles, muskrats. They have an elongated muzzle and an elongated proboscis. Insectivores have small teeth and five-toed feet. Many of them have scent glands near the root of the tail or on the sides of the body.

Shrews are the smallest representatives of insectivores. They live in meadows, bushes, and dense forests. These animals are voracious and attack small animals. IN winter time they make passages under the snow and find insects.

Moles are animals that lead an underground lifestyle. They dig numerous holes with their front legs. The mole's eyes are poorly developed and appear as black dots. The ears are in their infancy. The short, thick coat does not have a specific direction and lies tightly to the body when moving. Moles are active all year round.

Chiroptera

Squad The bats or Chiroptera includes animals of medium and small sizes that are capable of long flight. In the subtropics and tropics they are especially numerous. These type of teeth. The most common in our country are earflaps, leather boots, and vechnitsy. They settle in the attics of houses, in tree hollows, and in caves. During the day they prefer to sleep in their shelters, and at dusk they go out to catch insects.

Rodents

This order unites a third of the mammal species inhabiting our planet today. These include squirrels, gophers, rats, mice and other animals of medium and small size. Rodents for the most part are herbivorous animals. They have highly developed incisors (two in each jaw), molars with a flat chewing surface. Rodent incisors have no roots. They constantly grow, self-sharpen and wear off when eating food. Most rodents have a long intestine with a cecum. Rodents lead an arboreal lifestyle (dormouse, flying squirrels, squirrels), as well as a semi-aquatic (muskrat, nutria, beaver) and semi-subterranean (gophers, rats, mice). These are fertile animals. Most of them have cubs born blind and naked. This usually occurs in nests, hollows and burrows.

Lagomorpha

This order unites various pikas and pikas - animals that are similar in many ways to rodents. Main hallmark lagomorphs have a specific dental system. They have 2 small incisors behind the 2 large upper ones. Hares (hares, hare) feed on the bark of bushes and young trees, and grass. They come out to feed at dusk and at night. Their cubs are born sighted, with thick fur. Unlike hares, rabbits dig deep holes. Before giving birth to naked and blind cubs, the female makes a nest from the fluff that she pulls out of her chest, as well as from dry grass.

Predatory

Representatives of this order (bears, stoats, martens, lynxes, arctic foxes, foxes, wolves) usually feed on birds and other animals. The predatory mammal actively pursues its prey. The teeth of these animals are divided into incisors, molars and canines. The most developed are the canines, as well as 4 molars. Representatives of this order have a short intestine. This is due to the fact that the predatory mammal eats easily digestible and high-calorie food.

Pinnipeds

Let's move on to the consideration of pinnipeds. Their representatives (walruses, seals) are large predatory marine mammals. The body of most of them is covered with sparse coarse hair. The limbs of these animals are modified into flippers. A thick layer of fat is deposited under their skin. The nostrils open only during inhalation and exhalation. When diving, the ear openings close.

Cetaceans

True marine mammals - whales and dolphins - are included in this order. Their body is fish-shaped. These marine mammals for the most part do not have hair on their bodies - they are preserved only around the mouth. The forelimbs have been transformed into flippers, but the hind limbs are missing. In the movement of cetaceans great importance has a powerful tail that ends in a caudal fin. It is incorrect to say that marine mammals are fish. These are animals, although in appearance they resemble fish. Representatives of cetaceans are the most large mammals. The blue whale reaches a length of 30 meters.

Artiodactyls

This order includes medium-sized and large omnivorous and herbivorous animals. Their legs have 2 or 4 toes, most of them are covered with hooves. Based on the structural features of the stomach and methods of feeding, they are divided into non-ruminant and ruminant animals. The latter (rams, goats, deer) have incisors only on the lower jaw, and the molars have a wide chewing surface. Non-ruminants have a single-chamber stomach, and their teeth are divided into molars, canines and incisors.

Odd-toed ungulates

Let us continue to describe the orders of mammals. Even-toed ungulates are animals such as horses, zebras, donkeys, tapirs, and rhinoceroses. Most of them have developed toes on their feet, on which there are massive hooves. Today, only Przewalski's horse has survived.

Primates

These are the most highly developed mammals. The order includes prosimians and apes. They have grasping five-fingered limbs, with the thumb opposed to the rest. Almost all primates have a tail. The vast majority of them live in the subtropics and tropics. They inhabit mainly forests, where they live in small family groups or herds.

Mammals, birds, reptiles, amphibians - all of them can be described for a very long time. We have only briefly described the animals and described the existing units. The mammal family is diverse and numerous, as you have just seen. We hope that getting to know him was useful to you.

Class Mammals (Mammalia) is the highest class of vertebrates, crowning the entire system of the animal world. The most important features of the general organization of mammals are:

· high level development nervous system, providing complex and advanced forms of adaptive response to influences external environment and a coherent system of interaction between various organs of the body;

· viviparity, combined (unlike other viviparous vertebrates, such as fish and reptiles) with feeding the young with milk. It ensures better safety of young animals and the possibility of reproduction in a very diverse environment;

· a perfect heat regulation system, thanks to which the body has a relatively constant temperature, i.e. constancy of the internal environment of the body. It is easy to imagine the enormous significance this has for the distribution of mammals in a variety of living conditions.

All this contributes to the almost universal distribution of mammals across the Earth, in which they populate all living environments: air-ground, water and soil-ground. The following can be noted in the structure of mammals. Their body is covered with hair or wool (there are rare exceptions of a secondary nature). The skin is rich in glands that have diverse and very important functional significance. Particularly characteristic are the mammary (mammary) glands, which are not even hinted at in other vertebrates. The lower jaw consists of only one (dentary) bone. In the middle ear cavity there are three (and not one, as in amphibians, reptiles and birds) auditory ossicles: the malleus, the incus and the stapes. The teeth are differentiated into incisors, canines and molars; sit in the alveoli. The heart, like that of birds, is four-chambered, with one (left) aortic arch. Red blood cells are without nuclei, which increases their oxygen capacity.

There are about 4,500 species of living mammals. Modern science about mammals involves not only knowledge of the patterns of their organization and life activity, but also the study of the biological foundations of fauna management. The appearance of mammals is diverse. This is explained by the amazing diversity of their living environment - ground surface, tree crowns, soil, water, air. The body sizes of mammals also vary greatly: from 2 cm with a mass of 1.5 g in the pygmy shrew to 30 m and even more with a mass of about 150 tons. blue whale, which corresponds to the mass of 30 elephants or 150 bulls. The skin, like that of other vertebrates, consists of two layers: the outer - epidermis and the inner - cutis, or the skin itself. The epidermis, in turn, is divided into two layers: the deep, germinal (otherwise known as malpighian), consisting of living, dividing cells, and the outer, represented by cells that gradually die off due to horny degeneration. The most superficially located cells become completely keratinized and slough off in the form of small dandruff or whole flaps (in some seals). Due to the activity of the epidermis in mammals, such derivatives as hair, nails, claws, hooves, antlers (except for deer), horny scales and skin glands arise. The skin itself is highly developed and consists mainly of fibrous tissue. The lower part of this layer is loose, and fat is deposited in it - this is the so-called subcutaneous fatty tissue. The skin itself is especially strongly developed in aquatic animals - seals and whales, in which it plays a thermal insulating role and reduces body density. The overall thickness of the skin varies among different mammal species. As a rule, terrestrial inhabitants of cold countries with luxuriant hair have less hair. There is also a difference in the strength of the leather. A kind of cutaneous tail autotomy occurs in mice, jerboas, and especially in dormouse. Their skin caudal sheath easily breaks off and slides off the caudal vertebrae, which allows the animal grabbed by the tail to escape from the enemy. The same biological significance The skin of hares is also very thin, fragile and poor in blood vessels. The skin of mammals has significant thermoregulatory significance. The role of the fur is clear, but it is also necessary to point out the importance of the skin blood vessels. With the expansion of their lumens, which are regulated by neuroreflex mechanisms, heat transfer increases sharply. In some species of mammals, the evaporation of sweat secreted by the glands of the same name from the surface of the skin is also essential. Skin glands in mammals, unlike reptiles and birds, are abundant and diverse. Sweat glands are tubular, their deep parts look like a ball. These glands secrete mainly water in which urea and salts are dissolved. Not all mammalian species have the same development of sweat glands. There are few of them in dogs and cats; many rodents have them only on their paws, groin area and lips. There are no sweat glands at all in cetaceans, lizards and some others. The sebaceous glands are grape-shaped, and their ducts open into the hair follicle. The secretion of these glands lubricates the surface of the epidermis and hair, protecting it from wear and wetting. In addition, secretions of the sebaceous and sweat glands give the animal and its tracks a specific odor and thereby facilitate communication between individuals of the same species and between different types. The odorant glands of mammals are a modification of the sebaceous or sweat glands, and sometimes a combination of both. The significance of the glands is varied. Their secretions help to recognize individuals of different sexes, serve to mark occupied territory, promote sexual arousal, and serve as a means of protection from enemies. These are the musk glands of musk deer, muskrats, shrews, muskrats, the anal glands of carnivores, the ungulate and horn glands of goats, chamois and other artiodactyls. The anal glands of the skunk are well known, the secretion of which is extremely caustic and serves to protect against enemies. The mammary glands arose as a modification of the sweat glands. In lower monotreme mammals, they retain a simple tubular structure, and their ducts open on a certain area of ​​the skin of the abdominal surface. In this case there are no nipples. In marsupials and placentals, the mammary glands are cluster-shaped, and their ducts open on the nipples. The location of the glands and nipples varies. U bats and in monkeys they are located on the chest, and there is one pair of nipples. In most ungulates, the nipples, like the glands themselves, are located in the groin area. In other animals, the mammary glands and nipples are located on the belly and chest. The number of nipples is to a certain extent related to the fertility of the species. The maximum number of them is 24 (possums from marsupials, tenrecs from insectivores).

Hair is the most characteristic epidermal formation of mammals. Its absence in some species (for example, cetaceans) is a secondary phenomenon. Although hair is a derivative of the epidermis, during development its rudiment - the hair follicle - penetrates deeply into the thickness of the skin itself, forming a hair follicle. The corium papilla with blood vessels and nerves protrudes into the bottom of the hair follicle. This is the so-called hair papilla. The formation and growth of hair occurs due to the reproduction and modification of cells of the bulb, and the hair shaft is already a dead formation, incapable of growth. There are three layers in the hair shaft: the outer skin, the cortex and the core. The top two layers consist of flat keratinized cells and, as a rule, contain a coloring pigment. The core consists of dried cells filled with air, which gives the wool low thermal conductivity. The hairline of mammals consists of different types of hair. Their main categories will be downy hair, awn and sensory hair, or vibrissae. In most species, downy hairs develop predominantly, forming the undercoat, or down. However, in some animals, such as deer, wild boars, and many seals, the undercoat is reduced, and the hair coat consists mainly of awns. On the contrary, underground mammals (mole, mole rat, zokor, etc.) have almost no guard hairs. In most species, the hair on the surface of the skin is distributed unevenly, collected in tufts consisting of guard hairs, around which there are several downy hairs (from two to two hundred). There is a periodic change of hair coat, or molting. In some species it occurs twice a year - in autumn and spring; such are squirrels, some hares, arctic foxes, and foxes. Moles also have a third, summer moult. Gophers and marmots molt once a year, in spring and summer. In northern mammals, the thickness of their fur changes with the seasons, and in some, their color. So, a squirrel has an average of 4200 hairs per 1 cm2 on its rump in summer, and 8100 in winter. For the winter, ermines, weasels, arctic foxes, white hares and some others turn white. Special category Hair is represented by vibrissae - very long, hard hair that performs a tactile function. They are located on the head, lower part of the neck, chest, and in some climbers (for example, squirrels) - on the belly. Modifications of hair are bristles and needles.

In addition to hair, there are horny scales on the skin of mammals. They are most strongly developed in lizards. Horny scales are also observed on the paws (mouse-like rodents) and on the tail (mouse-like rodents, beavers, muskrats, and some marsupials). The horny formations will be the hollow horns of ungulates, nails, claws, and hooves. Deer antlers are also skin appendages, but they develop from the cutis and consist of bone material.

The muscular system of mammals is highly differentiated due to the variety of body movements. There is a diaphragm - a dome-shaped muscle that separates the abdominal cavity from the chest cavity and has important during ventilation of the lungs. The subcutaneous muscles are well developed. In hedgehogs, lizards and some armadillos, it ensures the body curls into a ball. The same muscles determine the bristling of animals, the raising of quills in hedgehogs and porcupines, and the movement of whiskers. On the face these are facial muscles.

The skull is characterized by a relatively large braincase, which is naturally associated with a large brain volume. The bones of the skull in mammals fuse late, allowing the brain to grow larger as the animal grows. Characteristic is the fusion of a number of bones into complexes. Thus, the four occipital bones form one; fusion of the ear bones leads to the formation of a single petrous bone; The temporal and sphenoid bones have a complex origin. Specific feature is the structure of the lower jaw, consisting only of the dentary bone. The angular bone gives rise to the tympanic bone, characteristic only of mammals, located in the form of an ovoid swelling at the bottom of the brain part of the skull. The articular bone, which in reptiles was also part of the lower jaw, turns into one of the auditory ossicles of the middle ear - the malleus. The lower jaw is attached to the skull (to the temporal bone) directly, since the quadrate bone, to which the lower jaw is attached in reptiles and birds, has also been modified into the auditory ossicle - the anvil. The structure of the spinal column in mammals is characterized by flat articulating surfaces of the vertebrae and a clearly defined division of the spine into sections: cervical, thoracic, lumbar, sacral and caudal. The first two cervical vertebrae are transformed into the atlas and epistropheus, and the total number of cervical vertebrae is seven. Thus, the length of the neck in mammals, unlike birds, is determined not by the number of vertebrae, but by their length. The only exceptions are sloths and manatees, in which the number of cervical vertebrae varies from six to ten. There are two true sacral vertebrae, but usually two more caudal vertebrae are fused to them. The basis of the shoulder girdle is the scapula, to which a rudimentary coracoid grows, and only in monotremes the coracoid is represented by an independent bone. The clavicle is present in species whose forelimbs move in different planes, such as monkeys. Species that move these limbs in one plane, such as ungulates, do not have clavicles. The limbs of mammals are quite typical of terrestrial vertebrates, but the number of fingers varies from five to one. A reduction in the number of fingers or rudimentation of the outermost ones is observed in fast running species, such as ungulates and jerboas. Relatively slow-moving animals, such as bears and monkeys, rely on their entire palm and foot when walking (plantigrade species); fast runners, such as dogs, ungulates, rely only on their fingers (digitate species). The digestive tract is characterized by a large length and well-defined division into sections. It begins with the vestibule of the mouth, located between the fleshy lips (characteristic only of mammals) and the jaws. In some animals, expansion of the vestibule leads to the formation of large cheek pouches (hamsters, chipmunks, ground squirrels, and some monkeys). Monotremes and cetaceans do not have fleshy lips. The ducts of the salivary glands open into the oral cavity, the secretion of which not only moistens food, but also chemically acts (the enzyme ptyalin) on starch, converting it into sugar. The saliva of desmodes that feed on blood has an anticoagulant property, i.e. prevents blood clotting. In some insectivores, saliva is poisonous and is used to kill prey. The teeth of mammals are differentiated into groups, depending on the type of food. Weak differentiation is characteristic of poorly specialized insectivores (shrews). In toothed whales, differentiation of teeth disappeared for the second time. The stomach, which has numerous glands, has different volumes and internal structure. The stomach of ruminant ungulates is the most complex, absorbing a huge mass of low-calorie and indigestible feed. Lizards and anteaters have no teeth, and the stomach, like that of birds, consists of two sections: glandular and muscular. The similarity is strengthened by the fact that in the second, deliberately swallowed pebbles are found, which ensure the grinding of food. In addition to the small, large and rectal sections of the intestine, some mammals also have a blind section, in which food is subjected to bacterial fermentation. The cecum is especially strongly developed in those feeding on rough plant foods; its length reaches a third of the length of the intestine. The ducts of the liver and pancreas empty into the anterior part of the small intestines. The lungs have a complex cellular structure. The smallest pulmonary passages - bronchioles - end in vesicles - alveoli, in the walls of which the thinnest blood vessels branch. The number of alveoli even in sedentary animals (for example, sloths) is 6 million, and in very active carnivores it reaches 300–500 million. The breathing mechanism is determined by a change in the volume of the chest as a result of the movement of the intercostal muscles and the diaphragm. The number of respiratory movements in mammals depends on the size of the animal, which determines the different metabolic rates. It is (per 1 minute): for a horse – 8–16, for a black bear – 15–25, for a fox – 25–40, for a rat – 100–150, for a mouse – about 200. Ventilation of the lungs not only ensures gas exchange, but it also has thermoregulatory significance. As the temperature rises, the number of respirations increases, and at the same time the amount of heat removed from the body also increases. Thus, in a dog, the ratio of heat transfer during breathing to the total heat loss at an air temperature of 8 ° C is (in percent) 14, at 15 ° C - 22, at 30 ° C - 46. Circulatory system mammals are similar to those of birds. The heart is completely divided into two atria and two ventricles; One aortic arch departs from the left ventricle (but not the right one, like in birds, but the left one). The aortic arch sends the carotid arteries to the head and, bending around the heart, stretches under the spinal column, along the way directing branched vessels to the organ systems. The venous system is characterized by the absence of portal circulation in the kidneys, which is well developed in the liver, as in other vertebrates. The liver neutralizes toxic products of protein metabolism. The size of the heart varies depending on the size of the body, lifestyle, and ultimately due to the intensity of metabolism. The weight of the heart, expressed as a percentage of the total body weight, is: in toothless whales –0.6–1.0, in a wild rabbit –3.0, in a mole –6.0–7.0, in bats –9, 0–15.0. All these features provide mammals with a higher level of metabolism and general vital activity.