Internal structure of a chicken. Chicken reproductive organs: anatomy and physiology Chicken anatomy description of organs

Compared to other vertebrates, the anatomy and physiology of the body of birds has some features that show many unusual adaptations, mainly to facilitate flight.

The skeleton consists of very light bones. They have large air cavities (called pneumatic cavities) that connect to the respiratory system. The bones of the skull in adults are fused and do not show cranial sutures. The orbits are large and separated by a bony septum. The spine has cervical, thoracic, lumbar and caudal sections, the number of vertebrae of the neck varies greatly and is especially flexible, but movement is reduced in the thoracic spine and is absent in subsequent sections of the spine. The vertebrae of the pelvis are fused to form a complex sacrum. The ribs are flat and the muscles of flight are attached to the sternum, with the exception of non-flying birds. The forelimbs are modified into wings.

Like reptiles, birds' kidneys extract nitrogenous waste from their blood and excrete it as uric acid, instead of urea or ammonia, through the ureters into the intestines. Birds do not have a bladder or external urethra and (with the exception of the ostrich) uric acid is excreted from the body in the feces as a semi-solid waste. However, birds such as hummingbirds can excrete most of the nitrogenous waste as ammonia. In addition, they secrete creatine rather than creatinine like mammals. This material, as well as the intestinal output, exits the bird through the cloaca. The opening of the cloaca is multi-purpose: feces are excreted through it, most birds mate through it, and females lay eggs through it. Males of ratites (except kiwi), Anseriformes (except screamers), and in a rudimentary form of Galliformes (but fully developed in Crax) have a penis, which is never present in neopalatines. Length is believed to be related to sperm count. When not copulating, it is hidden in the proctodeum compartment in the cloaca, just inside the vent. Birds' digestive system is unique, with a stomach that contains ingested stones for grinding food to compensate for the lack of teeth. Most birds are highly adapted for fast digestion, which facilitates flight. Some have adapted to use protein from many parts of their bodies, including protein from the intestines, as extra energy during pregnancy.

They have one of the most complex respiratory systems of all animal groups. When you inhale, 75% of the fresh air bypasses the lungs and flows directly into the posterior air sac, which extends from the lungs and connects to the air spaces in the bones and fills them with air. The remaining 25% of the air enters directly into the lungs. When a bird exhales, this air leaves the lungs and stored fresh air from the posterior air sac simultaneously passes through the lungs. Thus, the bird’s lungs receive a constant flow of fresh air both during inhalation and exhalation. Sound is produced by the fistula, a muscular chamber containing several eardrums that radiate from the lower end of the trachea, elongated in some species, increasing the volume of vocalizations and the perception of bird size. The bird's heart consists of four chambers, like the heart of mammals. In birds, the main arteries that receive blood from the heart come from the right aortic arch. The inferior vena cava receives blood from the extremities using the renal portal system. Unlike mammals, circulating red blood cells in birds retain their nucleus.

The nervous system is large relative to bird size. The most developed part of the brain is the one that controls flight functions, while the cerebellum coordinates movement and the cerebrum controls behavior patterns, navigation, mating and nesting. Most birds have a poor sense of smell with exceptions including kiwis and vultures. Bird vision is usually well developed. Waterfowl have special flexible lenses that allow them to see clearly in the air and water. The bird's eye absorbs ultraviolet rays well. The bird's eyelids are not used when blinking. The eyes are lubricated by a nictitating membrane, the third eyelid, which moves horizontally. The nictitating membrane also covers the eye and acts as a contact lens in many waterfowl. Most birds cannot move with their eyes, although there are exceptions such as the Great Cormorant. Birds with eyes on the sides of their heads have a wide field of view, while birds with eyes on the front of their heads, like , have binocular vision and can judge depth of field. A bird's ear does not have external feathers but is covered with feathers, although in some birds, such as ostriches, these feathers form tufts that resemble ears. The inner ear has a cochlea, but it is not a spiral like in mammals.

Several species may use chemical defenses against predators. Some can spit out a nasty oil against an aggressor, and some species of blackbird flycatcher from New Guinea have a powerful neurotoxin in their skin and feathers.

Chromosomes.

Birds have two sexes: male and female. The sex of a bird is determined by the Z and W sex chromosomes, and not the X and Y chromosomes present in the body of mammals. Male birds have two Z chromosomes (ZZ), while female birds have a W chromosome and a Z chromosome (WZ).

In almost all bird species, the sex of an individual is determined at fertilization. However, one recent study suggests that sex may be affected by temperature.

Knowing chicken anatomy, skeletal structure, and the functioning of organs when raising poultry is useful for the correct slaughtering and processing process. This knowledge will be useful in treating poultry from all sorts of diseases. The structure of a chicken has features that distinguish it from other birds.

The anatomy of chickens differs from mammals in that they have specific organs that only birds have. Different parts of the body of poultry have specific functioning features. Internal organs are represented by several systems.

Digestive system

The laying hen's food digestion system begins with the beak, which receives unprocessed food. After passing through the stomach and intestines, undigested residues are excreted through the cloaca.

In the crop, food is moistened and processed. The chicken does not have teeth, so food is processed only in the beak.

Process of food digestion:

1. After moving through the esophagus, the food ends up in the bird's stomach. Here it is affected by gastric juice. Food undergoes fermentation. To clean it, laying hens swallow small stones. When processing carcasses, they are found in the stomach.
2. The food is then sent to the hen's small intestine. In this department, beneficial compounds are absorbed from food.
3. The resulting mass is sent to the large intestine. This is where feces are formed.

Interesting: Chicken intestines reach a length of 180 cm, which is 6 times the length of the bird’s body. But since food is digested quickly, laying hens are constantly looking for food.

Respiratory

It is impossible to describe in detail the structure of domestic birds without taking into account the respiratory organs. They begin with the nostrils, through which air masses enter the larynx, and are directed through the trachea to the bronchi.

At the point where the trachea diverges, the lower larynx is located. It plays the role of sound production. The bronchi are in contact with many air sacs located in the body of laying hens.

They are responsible for heat and gas exchange. The lungs of birds do not transform radically.

Important: The internal organs of a chicken grow rapidly, like the bird itself, so it is profitable to keep it in a small farm and on a large farm.

Nervous

Farm birds have well-developed nervous processes. This system includes the spinal cord and brain, as well as a network of processes that conduct nerve impulses.

The latter pass through the chicken's body, a few minutes after death. This explains the ability of birds to run around with their heads cut off.

Peculiarities:

1. The chicken brain consists of the cerebellum, forebrain, midbrain and diencephalon. These areas are homologous to human ones, that is, they are in the same position relative to each other, and are responsible for the same functions.
2. The hemispheres are small, and there are very few convolutions in them. Their functions are instinct control and orientation.
3. The cerebellum is responsible for motor function.

It is easy to distinguish these anatomical regions in a photo of a laying hen's brain.

excretory

Features of the excretory system of chickens:

1. It consists of large kidneys that open into the cloaca. As a result of the work of these organs, uric acid is released.
2. The structure of chickens does not provide for a bladder.
3. Birds have regular bowel movements, which allows them to lighten their weight for flight.

Thanks to these features of the excretory system, birds quickly gain weight.

You can examine the chicken in cross-section when opening it.

Blood

In laying hens it is represented by a heart with four chambers and two circles of blood circulation, separated from each other.

Pulmonary circulation:

1. Venous blood accumulates in the right atrium.
2. As a result of cardiac contraction, it enters the right ventricle.
3. Blood leaves the pulmonary artery and goes to the lungs, where it is oxygenated.
4. After this, it ends up in the left atrium.

Big circle:

1. Its origin is in the left ventricle.
2. The blood is then sent to the aorta.
3. After saturation with oxygen, it is transported to organs through the smallest vessels.

The hen's heart is under significant stress. Poultry have high blood pressure with a rapid heart rate (170–460 beats/min). This is due to accelerated metabolism and elevated body temperature – 41–42 degrees.

Reproductive

Birds reproduce by laying fertilized eggs. They then hatch into chicks. Roosters have symmetrical reproductive organs - testes.

They exit into the vas deferens, which flows into the seminal vesicle. Sperm are produced here.

The chicken's body is designed in the best way for egg production.

Gestation process:

1. The embryo is sent from the ovary to the facial tube. As it passes, it builds up protein.
2. After 4 hours, the egg takes shape and enters the hen’s oviduct. This is where its shell is formed.
3. Shell growth lasts about a day.
4. The egg exits through the cloaca.

Important: Males do not have a reproductive organ. The egg is fertilized after the cloaca of the rooster and the laying hen come into contact. The egg is formed in the bird's body in a minimum of 12 and a maximum of 48 hours.

The reproductive organs are represented by the oviduct and the left ovary. The right one atrophies as it gets older. The eggs are produced in the left ovary.

The oviduct resembles a long tube, ranging from 35 to 86 cm in length. It stores sperm from the moment of copulation until fertilization. This is where egg formation occurs.

The female's oviduct consists of five parts:

1. The funnel is placed on top and opens into the belly.
2. The protein part is up to 37 cm long. When the yolk passes through it, protein production occurs.
3. The isthmus connects the protein part with the infundibulum.
4. Uterus. This is the name of the muscular organ, a wide area of ​​the oviduct in which the shell is formed.
5. The vagina reaches a length of 5 cm.

The reproductive system of laying hens is similar to the reproductive system of humans, but with a simpler fertilization pattern.

Features of growth

Ancient reptiles were the ancestors of birds and mammals. A careful examination of the laying hen’s legs clearly shows that there are scales on the distal parts - they were inherited from a distant “relative”.

Distinctive features of birds:

1. Birds have a pronounced ability to fly. This feature determines the structure of the chicken.
2. Due to the short length of the large intestine, food is digested faster.
3. The metabolic rate of birds is 50 times higher than that of humans.
4. Presence of goiter and carina.

In other aspects, the bird is similar in structure to other species.

The chicken skeleton develops rapidly during the first 60 days. During this time, the chicken gains 70% of the adult mass. Bone growth slows down by the 130th day of life.

The skeletal features of birds are determined by their ability to fly:

1. Bones account for 10% of the mass of an adult.
2. There are air sinuses in the spine. Due to them, the bones are lightened.
3. Bone marrow makes up 2% of body weight. In humans it is represented by 4.5%.

These growth features of birds distinguish them from mammals.

Skeletal structure

Chickens fly rarely and for short periods of time, although they have many hollow bones. The chicken skeleton, regardless of breed, is similar to the skeleton of birds that fly well.

Important: The anatomy of chickens is different from the body structure of roosters. Laying hens have medullary bone, which influences the shape of the shell.

Other features of the skeletal structure of laying hens:

• The skull contains 10 bones;
• The large wing is represented by the clavicles, coracoid bone, scapulae and the movable part of the wing;
• The cervical vertebral column in chickens includes 13–14 parts;
• The chest zone contains 7 elements;
• The caudal region is represented by 5–6 vertebrae.

The thoracic region of birds has a keel. This is a protrusion that serves as an attachment point for the largest pectoral muscles. They are easy to palpate to assess the fatness of the chicken.

The forelimbs are represented by wings. Laying hens have 4 toes on their feet. Roosters have spurs. The legs consist of the tibia, the tarsus (located between the toes and the tibia) and the femur. These chicken body parts are of great value.

It is important to know the anatomy of birds for the treatment of diseases, slaughter and processing. By understanding the life functions of laying hens, the poultry farmer is able to achieve optimal egg production and growth.

Chicken entrails, like its meat, are valuable agricultural products.

The structure of a chicken must be presented to every novice poultry farmer and experienced farmer in order to promptly notice various ailments of the livestock and apply this knowledge when slaughtering and processing meat. In addition, understanding the anatomy of chickens is useful for those who want to improve egg production and growth of young animals.

The internal parts and the chicken carcass itself are sources of a variety of food products and are very popular among the average consumer.

This material examines the body systems that function in the bird’s body and provides general descriptions of activities and internal processes.

The main feature of the bird's anatomy is the bones, which are empty inside. This is explained by the fact that, like all other birds, theoretically a chicken can fly, but in practice this is not done regularly. Chickens rise in height briefly and infrequently, but at the same time their skeletal system resembles those who are quite active in this regard. Due to the air sinuses, the weight of the bones decreases.

In the first 2 months, the main growth of the chicken skeleton occurs and this continues until the individual reaches six months of age. Most of the body weight (up to 70%) is also gained in the first 60 days.

The total weight of the skeletal system rarely exceeds a tenth of the total mass.

The second distinguishing feature of the chicken skeleton is the absence of teeth. They are replaced by a dense beak, which is a standard horny process. This is the difference between chickens and humans and mammals.

Also, animals and people have an increased bone marrow mass (about 5% of the total) compared to chicken - its bone marrow accounts for 2 percent of body weight.

It is believed that the ancestors of birds and mammals were reptiles that lived during the era of dinosaurs. If you carefully examine the appearance of laying hens, you will notice characteristic scales on their legs, characteristic of an extinct group of living creatures.

The internal structure of birds is simple

Skeletal system

The skeletal system combines the head, trunk and limbs. Sometimes it seems that the head looks disproportionate against the background of a more voluminous body, but this is a feature of the skeleton.

The cervical region includes 13 or 14 vertebrae, the thoracic region - 7 pieces, the tail consists of 5-6 movable vertebral parts. In the thoracic spine there is a specific component called the keel. The largest pectoral muscles in the chicken’s body are attached to it, which can be easily felt when assessing the fatness of the bird.

1. The coracoid system.
2. Scapular region.
3. Collarbone.
4. That area of ​​the wing that is free and combines several sections - radial, humeral, ulnar.

Chicken wings do not perform the function of frequent flights, but are still necessary
The wings are the forelimbs, which include:

From the back, the legs of chickens are paws with claws. Roosters additionally have structures such as spurs. The paws are in close contact with the pelvic region and include the lower legs, the tibia and tibia, as well as the thighs and that part of the body that is commonly called the tarsus. The latter is located between the fingers and ankle. Most chickens have four toes, but there are also breeds with more.

Young, growing laying hens have medullary bone, which is not characteristic of roosters. It is involved in the formation of the shell around eggs and begins to function at puberty.

Features of bones

Chicken bones mainly contain the following microelements: calcium, phosphorus (99% and 90%, respectively - poultry bones are storage reservoirs). In addition, they include thin collagenous fibrous elements closely intertwined with each other. The skeleton of a chicken is as reliable as a human one, and this is due to its structural features.

It is important for poultry to receive vitamin D. This brings the chicken skeleton into proper shape and condition. If, as a result of vitamin deficiency, calcium ceases to be absorbed, the egg shells will become soft or stop forming altogether.

The extreme stage of lack of the “sunshine vitamin” is manifested in the suspension of laying.

If we are talking about cellular metabolism, then calcium also manifests itself in a deficient form. Characteristic signs are osteoporosis, muscle weakness and related disorders, including paralysis. To cure a bird, you need to plant it on the ground and give it dietary calcium as a dietary supplement.

There are two types of bones in a chicken's body.

Table 1. Types of chicken bones

It must be said that the neck and spinal column of a chicken are quite flexible. The latter includes 39 bone elements. And the neck is long enough to search for food everywhere.

The largest bone in the system is the sternum, which covers half the body. The wings are attached to the sternum by special muscles.

The legs of laying hens and roosters are similar in structure to the legs of people. The only difference is that the human hip is in close connection with the spine. Thanks to this, it is securely and rigidly attached. This position strengthens the powerful muscle corset.

Internal anatomy of a domestic chicken

In comparison with the usual scheme relevant for mammals, the anatomy of chickens has a number of specific features.

Digestive tract

Food ends up in the bird's beak. The intermediate link of movement is the goiter, and the final section of the digestive system is the cloaca.

The bird takes food into its beak, swallowing it; the crop is needed for primary fermentation, since birds do not have teeth. This is due to the fact that teeth would weigh down the skeletal structure and make the bird's structure more bulky.

The crop is a “stop” where the nutrient mass accumulates and from where it enters the stomach, gradually moving forward for digestion in the glandular and muscular parts.

The chicken esophagus is a long muscular tube. During the movement of food particles along it, they are not fermented and are not affected by juices. The glandular part of the stomach begins digestion, since it is in this section that the acids and enzymes necessary for digestion are secreted.

After gastric digestion, food enters the duodenum. Then the resulting mass goes further into the thin section. In both, it begins to be absorbed, providing the organs and systems with complete nutrition with vitamins and microelements. Untreated residues enter the environment in the form of feces through the cloaca. The large intestine is responsible for timely bowel movements.

Digestion in chickens is rapid. The only exception is the coarse parts of the grain, which may take longer to digest.

An interesting fact is that chicken intestines are 180 centimeters long. This figure is 6 times greater than the same figure for the body. Due to the fact that digestion takes place quickly, laying hens are in an eternal search for food.

In general, a young bird digests food in about 4 hours. When a clutch is observed, the process takes 8 hours; brood hens digest and absorb nutrients for 12 hours.

Respiratory system

When flying, an ordinary bird consumes a lot of oxygen. This is due to the atypical structure of the respiratory system. Chickens are no exception, although they fly in exceptional cases. The first link is the nostrils. After getting inside, the air passes through the nasal cavity, then along the laryngeal part and, finally, into the trachea, in order to divide into streams and go to the bronchi.

In this place, where the trachea is divided into parts, the characteristic vocal “accompaniment” of each bird, including chickens, is formed

It is noteworthy that in birds, including domestic chickens, the bronchi continue outside the lungs and are tightly connected to the air sacs, which are located directly in the body. This property unites them with ancient reptiles that went extinct millions of years ago. According to scientists, dinosaurs breathed using similar air sacs, where up to 75% of the inhaled air could settle.

Chicken lungs hardly change in volume when breathing, since they do not have the ability to stretch, like mammals. There are no valves in this system of the avian body. Any movement occurring inside it is subject to thermodynamic laws. Additional functions of the respiratory organs are thermoregulation and gas exchange.

Circulatory organs

The chicken circulatory system includes organs:

1. Heart system with 4 chambers.
2. Pulmonary circulatory system.
3. Systemic circulatory system.

Both circles are disconnected. This means that venous blood always moves through the vessels separately from arterial blood. The first collects in the right side of the heart muscle, called the atrium, to then enter the ventricle on the right side. The enriched blood then passes through the lung into the left atrium. So it moves in a small circle.

As for the large circle of motion, it looks like this:

1. This part of the circulatory system originates in the left side of the heart - the ventricle.
2. Next, from the aorta, blood fluid is supplied to organs and systems through a network of small blood vessels.

The heart muscle of a chicken is quite large if you compare it as a whole with the dimensions of a bird. Externally it is asymmetrical. This is due to the functional work of the organ, the left side of which pumps more blood.

High heart rates and blood pressure are considered normal in chickens. Thanks to this, the chicken’s body has a fast metabolism, as well as a high temperature.

Table 2. Norms of heart rate and body temperature

Excretory organs of chickens

The excretory system combines paired kidneys, as well as ureters, which connect the main organs to the cloaca. This is how urine is released.

Birds do not have a bladder, like in humans and animals. Water, saturating the body, is processed and exits directly into the cloaca.

This is associated with the atypical appearance of chicken urine. It is thick and resembles a mushy substance. It is not so easy to distinguish the liquid secretions of chickens from their feces. In addition, a chicken urinates much more often than a mammal - urination occurs as often as stool.

Nature has provided birds with ease of movement, including through a unique system for removing fluid from the body and forming feces.

Reproductive organs and reproductive system

Like other birds, chickens reproduce by laying and incubating eggs. Their body is perfectly adapted for this.

Males fertilize females with the help of testes located near the kidneys, from where, during the breeding season, sperm enter the chicken’s body through the spermatic ducts. Chickens do not have external genitalia - the process occurs directly when the cloacas come into contact.

During the breeding season, the testes reach more impressive sizes.

As for females, only their left ovary has proper development. The right one atrophies by the time the chicken reaches adulthood. It is located in the area of ​​the kidneys, like the testes of roosters. Then it passes into the left oviduct. The structure of the chicken's reproductive system is completed by an expanded funnel. It, in turn, turns into a twisted thick-walled pipe, which has an outlet into the cloaca.

Eggs, like those in humans and mammals, appear in the ovary. The peculiarity of reproduction is that only the left ovary has this function. Eggs are a very valuable product, as they contain all the essential nutrients needed for the process of gestation and birth of chicks.

The oviduct is divided into sections in its structure. The first of these is the fallopian tube, followed by the uterus. In many ways, the system resembles the human and animal reproduction systems. The length of the oviduct is from 35 to 86 centimeters.

If oviposition occurs intensively and for a long time, the ovary reacts immediately and externally becomes 10 times larger.

The pattern of birth of offspring in chickens is more primitive compared to humans and animals.

From the time the egg is released into the oviduct, from half a day to two days will pass. The oviduct performs another important function - the egg itself is formed in it.

The breeding scheme is as follows:

1. Before becoming a real egg, the embryo moves from the ovary and gradually builds up protein.
2. Then, after four hours, the egg becomes its usual shape and then enters the oviduct. The appearance of a dense shell of the egg occurs here. This happens within 24 hours or a little less time.

A baby chicken can move independently and stand almost immediately after birth.

When mating occurs, the hen can store the rooster's sperm in the pockets of the oviduct and remove them from there if necessary. Sperm viability is 1 month. It can be used to fertilize eggs within the specified period.

Organs of the nervous system

Chickens have a brain and a spinal cord. Their nervous system also includes special processes and fibers that allow nerve impulses to travel throughout the body.

The body of chickens is designed in such a way that nerve impulses can travel through the internal organs and systems for some time after the death of the bird.

In the brain, the system is represented by the anterior, intermediate sections, as well as the middle section and the cerebellum. Chicken hemispheres are not large in size. They are responsible for orientation in space, as well as the implementation of the bird’s basic instincts. In the cerebellum, impulses are processed properly, turning into coordinated movements.

An interesting feature is that the parts of the brain are located relative to each other like humans. Their functionality is also identical, despite the minimal number of convolutions in the hemispheres.

Conclusion

Chickens are important objects in the economic and production part. Their meat is extremely popular, but few people understand how poultry's body systems work and how it affects performance. To do this, it is necessary to expand knowledge about the internal structure and delve a little deeper into the anatomical component.

Video - How a chicken egg is formed

Video - Opening a chicken

Introduction

The class of birds is divided into ratites and keels. The latter include the orders Anseriformes and Galliniformes.
The structure of the body in representatives of the class of birds is associated with their peculiarity of movement, which is their adaptation to flight. For example, changes in the structure of the thoracic limbs, lightening of most organ systems, the presence of feathers, the presence of large air sacs, etc.

Skeleton.
The skeleton of birds is particularly light due to pneumatic bones (i.e. containing air cavities), as well as structural features. The spinal column, as in mammals, is represented by the cervical, thoracic, lumbar, sacral and caudal sections.
The cervical region is represented by a larger number of vertebrae than in mammals (chickens 13-14, ducks 14-15, swans 23-25, geese 17-18, ostrich 18-20), and is S-shaped. The spinous processes are poorly developed or completely absent, the ventral ridges are well defined, and rudiments of ribs directed caudally are visible on the transverse processes. The intertransverse foramina form the cervical canal, in which the artery, vein and sympathetic nerve pass. The vertebral bodies are connected by saddle-shaped joints to cartilaginous layers, which ensures high mobility of the cervical spine.
The thoracic region is formed by 7 (chickens) or 9 (ducks and geese) sections. The second to fifth vertebrae are fused into a single whole. The first 1-3 ribs in birds are asternal, i.e. do not reach the sternum. Each complete rib is divided into vertebral and sternal bony sections. The vertebral portions of the ribs are carried along the uncinate process (processus uncinatus), which is directed caudally and joins the subsequent rib, which provides strength to the chest. The lower ends of the vertebral sections are connected to the sternal ones through joints, located almost at a right angle. The sternum is very strongly developed, its inner surface is concave, and its outer convex surface has a massive keel, or sternum crest (carina s. crista sterni) on the sagittal plane. The pectoral muscles are attached to it, thanks to which flight is carried out. Running birds do not have a crest. The posterior edge of the sternum has a paired notch of varying length in different species.
The pelvic region consists of 11-14 segments that fuse into one lumbosacral bone.
The caudal section consists of 5 (chickens) or 7 (ducks, geese) vertebrae, to which the coccyx, or pygostil, is attached at the very end, but to which the steering wings are strengthened.
The bird skull consists of the facial and brain sections. The brain section consists of early fused bones. The occipital bone has only one occipital tubercle for articulation with the atlas, the sphenoid bone has only temporal wings, and in the temporal bone the petrous bone and scales are fused. The interparietal bone is absent. Ethmoid bone without a developed labyrinth. The orbits are wide, deep, separated from each other by an interorbital bone plate.
The facial part of the skull is more complex, but its volume is relatively small. Its lightness is ensured by the absence of teeth and the special structure of the upper jaw, which has merged into a whole formation, movable in relation to the brain. The mandibular bone consists of two sections: cranial (dentary bone - os dentale) and caudal (articulated bone - os articulare). The square bone (os quadratum) is located inside the jaw joint, so the complex jaw joint and the system of movable bones of the skull create a mechanism for wide opening of the oral cavity.

The thoracic limb is greatly modified compared to mammals and is called a wing. The shoulder girdle is represented by the scapula, clavicle and coracoid. Thanks to this, the bird can make large and strong swings of the free part of the wing when flying. The scapula is devoid of scapular cartilage and has the appearance of a narrow plate. The coracoid bone (os coracoideum) is the most powerful, it connects to the scapula, humerus and clavicle. The clavicles are fused by the distal bones to form a fork or arch (furula). On the medial surface of the humeral wing there is a pneumatic opening leading to the air cavity of the bone (foramen pneumaticum). The ulna is more developed than the radius, and there is a significant interosseous space between them. The bones of the hand are reduced. The wrist is represented by the carpal radius and ulna bones. The metacarpus is reduced to three segments, merging into one formation, to which the distal row of the wrist is attached. The phalanges of the fingers are reduced, only the third finger with two phalanges is clearly preserved.
The ilium fuses with the lumbosacral region and extends over the ends of the last ribs on the thoracic limb. The pubic bones do not fuse together; the ventral wall of the pelvic cavity consists of muscles, connective tissue and skin. The femur is shorter than the tibia bones and has one trochanter. The body of the bone is curved dorsally. The tibia is long, and the proximal tarsus fuses with its distal section to form the tibiotarsus. The fibula is greatly reduced and fused with the tibia. The tarsal bones fuse with the 2nd, 3rd, and 4th metatarsal bones, forming the tarsometatarsal joint, or tarsus. The first metatarsal is small and articulates with the first toe. Proximal to it, roosters have a calcarine process. The skeleton of the fingers has 4 rays. The number and size of phalanges varies among different species.
Musculature.
In flightless birds or those that fly with difficulty, which include chickens, the muscles are pale, there are fewer red blood vessels in it, less myoglobin, glycolytic enzymes predominate, due to which they contract quickly, but fatigue sets in quite quickly.
The skin muscles are well developed, as some of them end on the feather sheaths. There are no facial muscles, but the masticatory muscles are well developed. The dorsal muscles of the thoracic and lumbar spine are very poorly developed due to the immobility of these sections. The abdominal muscles are represented by thin and weak layers. The neck muscles of birds are well developed and differentiated. The muscles of the wing and pelvic limbs are quite complex, the thigh muscles are especially massive.
Skin and its derivatives.
The skin of birds consists of the epidermis, the base of the skin and the subcutaneous layer. The skin does not contain sweat and sebaceous glands, the epidermis constantly peels off. Above the last sacral vertebrae there is a coccygeal gland (glandula uropigii), which functions like a sebaceous gland and serves to lubricate the feather cover (using the beak). Feathers are of great importance during flight and for thermoregulation, touch, protection and sexual demorphism. In poultry, there are contour (integumentary), filamentous, down and tassel feathers.
Molting in birds is juvenile (once in a lifetime) and seasonal (once a year). During the molting period, egg production stops in poultry.
Digestive organs.
The oropharynx of birds consists of the oral cavity and pharynx. The oral cavity lacks teeth, gums, cheeks and lips. The jaws are covered with a horny sheath - a beak, which consists of a mandible and a mandible.
The esophagus has a wide lumen and passes into the goiter (ingluves), which in chickens is represented before the entrance to the thoracic region by a unilateral protrusion of the esophagus on the right side. Accumulation and maceration of solid nutrient material occurs in it.
The stomach consists of glandular and muscular parts. The glandular part is located between the lobes of the liver as a continuation of the esophagus and contains glands. Tapering, it turns into a muscular, more pronounced in granivores, rounded large part. Its walls are formed by four large muscles of smooth muscle tissue. Shiny white tendon mirrors are visible on the outer surfaces. This part is functionally correlated with goiter. The tubular glands of the gizzard of many birds form the cuticle: a hard keratin shell that also helps mechanically process food (grind).
The duodenum emerges from the right side of the cranial edge of the muscular part of the stomach, forming a loop, between the knees of which the pancreas is located, secured by the pancreatic-duodenal ligament. The gland has two (ducks, geese) or three (chickens) lobes, from which a corresponding number of ducts arise.
Next comes the jejunum, about 1 meter long. In chickens, on the intestinal wall there is a remnant of the former yolk sac in the form of a small diverticulum. In 50% of chickens it is invisible, but in most geese and ducks it persists. The ileum lies between the right and left cecum and ends in the large intestine.
The liver in birds is relatively large, divided into two lobes, and held in place by the falciform ligament. Most birds have a gall bladder on its right lobe. The hepatic duct begins from the left lobe, which from the right lobe goes into the gallbladder, from which the cystic duct goes into the duodenum.
The large intestine is separated from the small intestine by a fold of mucous membrane, behind which there are two cecums. Further under the spine is the rectum, which flows into the cloaca.
The cloaca is the final part of the digestive tract. By two folds it is divided into three sections: cranial (coprodeum), middle (urodeum) and final (proctodeum). The ureters and excretory tracts of the genital organs open into the middle section. Defecation and elimination occur simultaneously with the help of the muscles of the intestinal wall and the pressure of the air sacs.

Respiratory organs.
The lungs of birds do not contain alveoli, like those of mammals, but consist of millions of thin parabronchi connected at the ends with dorsobronchi and ventrobronchi. A capillary runs along each parabronchi. The blood in them and the air in the parabronchi move in opposite directions. Gas exchange occurs through the airborne barrier
Due to their lifestyle, the respiratory organs of birds have several characteristic features that allow birds to ventilate their respiratory organs during flight:
1) simplicity of the structure of the nasal cavity;
2) the presence of a singing larynx;
3) the peculiar structure of the lungs, which occupy a small volume in the chest;
4) complicated development of air sacs.
The nasal cavity is divided by a septum into two halves, each of which contains the superior and inferior turbinates. There is no labyrinth of the ethmoid bone. The nasal cavity communicates by a fissure with the infraorbital cavity, in the wall of which the nasolacrimal canal passes.
In birds, there is an upper cranial larynx and a lower sound (singing) larynx, located in the bifurcation area. The singing larynx consists of parts: a drum, a bridge with a semilunar membrane and tympanic membranes (external and internal). The entrance to the larynx is covered by a mucous fold that replaces the epiglottis.
The trachea in the neck lies ventral to the spine and enters the chest cavity between the clavicles. The tracheal rings are solid. The bifurcation is located above the base of the heart.
The lungs are light pink in color and have a specific structure. In the lung tissue, gas exchange occurs through the walls of the air capillaries. The main bronchi pass through the lungs and end in the air sacs: when you inhale, air enters the lungs and fills the chest and abdominal sacs; when you exhale, air from these sacs passes through the lungs into the cervical and subclavian sacs. In the pleural cavity of the lungs there are thin fibers of connective tissue that connect the surface of the lungs to the chest wall. There are also 6 types of bronchi: main bronchus, second-order bronchi (without cartilage in the walls), ectobronchi (pass into the air sacs), recurrent sac bronchi (leading back to the lungs), endobronchi (directed dorsally and laterally inside the lungs), parabronchi (from The respiratory portions of the lung branch off from them). A number of air-bearing bronchi open into air-sacs, represented by protrusions of the mucous membrane, tightly covered with the serous membrane. They give off branches that penetrate the bones (with the exception of the skull). There are nine of them in both lungs: the interclavicular (unpaired) sac (saccus interclaviculares), cervical (sacci cervicales), cranial and caudal thoracic, or intermediate (sacci thoracici craniales et caudales), abdominal sacs (sacci abdominales). The bags serve as additional reservoirs for air, and also improve the act of breathing itself: birds receive oxygen not only when inhaling, but also when exhaling, which significantly increases the level of metabolism. Also, the axillary diverticula of the interclavicular sacs during flight act as bellows, replacing the movements of the chest. They also play a role in making sounds, emptying the cloaca, when swimming, and, very importantly, protect the body from overheating during flight.

Urinary organs.
The system of excretory organs in birds is noticeably simpler than in mammals. The kidneys do not have renal cups, a pelvis, and there is not even a clear distinction between the urinary and excretory zones. They lie in the ventral recesses of the lumbosacral spine and ilium. The urinary tubules, approaching the ventral (medial) edge of the kidney, unite into short branches, which open into the ureter. The ureter passes along the medial edge backward and opens into the middle part of the cloaca. Birds do not have a bladder.

Male genitals.
The testes are bean-shaped or ovoid, their size depends on the sexual cycle. Anchored in the abdominal cavity by a short mesentery. There are small appendages on the medial surface. The vas deferens meander and lead to the middle section of the cloaca, where they open on a small papilla in roosters. The drake has an analogue of the external genitalia. Birds do not have accessory gonads.
Female genitals.
The right ovary is reduced during embryonic development. The deep layer of the ovary is the deep zone. With age, the ovary becomes more and more lumpy due to maturing follicles. The eggs grow unevenly, the most mature ones droop on the stalk-like outgrowths of the serous membrane. After the egg emerges, a hollow cup (calyix) remains on the stem for some time.
The oviduct consists of a funnel (fundibulum), a protein part, an isthmus (istmus), an avian uterus and a vagina, which opens into the middle section of the cloaca. In the process of passing through the oviduct, a proteinaceous, and then a leathery, and finally a calcareous shell is formed.

Blood and lymph circulatory system.
The heart of birds is four-chambered, completely divided into right and left halves. There are no papillary muscles in the right ventricle. The atrioventricular orifice has a double muscular plate that serves as the valve of this orifice.
The right aortic arch is preserved. Another feature is the presence of two cranial vena cavae.
Lymph nodes are rare and are located in two places: at the entrance to the chest at the end of the jugular veins and in the lumbar region above the spine. On the dorsal side of the cloaca there is the bursa of Fabricius, an organ that is significantly reduced in adult birds (starting from 8-9 months of age), but functions normally in young birds. The bursa of Fabricius produces lymphocytes and oxyphilic leukocytes.
The spleen is small, round in shape, lying on the right side of the stomach.

Endocrine apparatus.
Represented by the pituitary gland, pineal gland, thyroid gland, parathyroid glands, thymus, adrenal glands and ultimobronchial glands.

Nervous system.
The medulla oblongata is strongly convex.
The cerebellum consists of a well-developed vermis and small lobes.
The midbrain consists of a well-defined colliculus and a wide cavity. The diencephalon has small visual tubercles.
The large hemispheres are characterized by the fact that they do not have convolutions and fissures (except for the Sylvian). The corpus callosum is absent, there are no ammonal horns, the lateral ventricles are wide. All cranial nerves are present, but some are poorly developed due to underdeveloped facial and some other muscles.

Sense organs.
The eyeball is relatively large. The sclera contains a cartilaginous plate, ossified at the transition to the cornea, and bone tissue at the exit site of the optic nerve. On the choroid near the exit of the optic nerve there is a ridge in the form of a wedge-shaped protrusion, the apex of which is attached to the lens capsule. There is a cartilaginous plate in the lower eyelid. The third eyelid is developed. The lacrimal gland is small with one excretory duct. Between the orbit and periorbit lies the Harderian gland.

The outer ear does not have an auricle; the entrance hole is covered with a fold of skin and feathers. The eardrum is attached to a bone ring. There is only one auditory bone in the middle ear - the column. The cochlea contains the auditory papilla (analogous to the cortical organ).

The olfactory analyzer is represented by cells in the dorsal turbinate. There are no taste buds on the tongue. There are taste endings in the mucous membrane of the tongue of chickens and taste buds in ducks and geese. Chicks have more taste buds.
Skin analyzers are represented by free nerve endings in the skin. There are especially many of them in the cerome at the border of the beak and the scalp. In ducks and geese there are also a lot of them in the rhamphotheca plates and in the cere covering the surface of the beak.

Veterinarian Artem Arkadievich Kazakov

Features of the body structure of poultry

The skeletal bones of agricultural birds often contain voids that are filled with air, making them lightweight. In birds, the skeleton of the body and tail (cervical, thoracic, lumbosacral and caudal sections), the skeleton of the skull or head and the skeleton of the limbs are distinguished. The cervical spine consists of 13-14 vertebrae in chickens, 14-15 in ducks, and 17-18 vertebrae in geese. The thoracic region consists of 7 segments in chickens, and 9 segments in ducks and geese, while the seventh thoracic vertebra is immovably fused with the lumbosacral region (Fig.).

I - incisor bone; 2 - nasal opening; 3- nasal bone; 4 - lacrimal bone; 5 - perpendicular plate of the ethmoid bone; 6 - dentary bone; 7 - palatine bone; 8 - quadratozygomatic bone; 9 - pterygoid bone; 10 - articular bone;

II - square bone; 12 - tympanic bone; 13 - atlas; 14 - cervical vertebrae; 15 - thoracic vertebrae; 16 - blade; 17 - ilium; 18 - caudal vertebrae; 19 - pygostyle; 20 - ischium; 21 - pubic bone; 22 - sciatic foramen; 23 - locked hole; 24 - femur; 25 - kneecap; 26-27 - fibula and tibia; 28 - metatarsus; 29 - first metatarsal bone; 30 - first finger; 31-32-33 - second, third and fourth fingers; 34 - sternum crest (keel); 35 - sternum; 36-37-38 - middle, lateral and costal processes of the sternum; 39-40 - sternal and vertebral sections of the ribs; 41 - uncinate process; 42 - collarbone; 43 - caracoid; 44 - humerus; 45-46 - radius and ulna bones; 47 and 48 - carpal and ulna bones; 49 - third metacarpal bone; 50, 51 and 52 - second, third and fourth fingers.

The breastbone is elongated, and on its surface there is a ridge called a keel. The lumbosacral region is represented by a monolith due to tightly fused lumbar and sacral vertebrae. The tail section in chickens consists of 5-6 and in ducks and geese, 7 vertebrae. They have some mobility.

The skeleton of the thoracic limbs consists of a narrow scapula, coracoid bone, clavicle and free wing skeleton (humerus, radius and ulna, two carpal bones, metacarpal bones and finger bones). The skeleton of the pelvic limbs consists of the pelvic girdle, which is fused with the lumbosacral spine and consists of the ilium, ischium and pubic bones. The free pelvic limb consists of the femur, tibia, tibia and fibula. There are no tarsal bones in adult birds, but the bones of the second, third and fourth metatarsals are fused and form the tarsus, or running bone. Roosters have a pshor process at the chic end of the tarsus. The pelvic limb ends with four fingers, with the first finger pointing backward, the second, third and fourth fingers pointing forward and having three, four and five phalanges, respectively.

Although birds are warm-blooded animals, there is still a lot of peculiarity in their structure. Thus, the head of birds is equipped with a beak, a crest, earrings, and sometimes a crest, sideburns and a beard (Fig. 9).

1 - comb; 2 - nostrils; 3 - beak; 4 - earrings; 5 - front neck feathers? 6 - chest; 7 - shoulder wing feathers; 8 - shin feathers; 9 - nail; 10 - finger; 11 - metatarsus; 12 - sole; 13 - spur; 14 - heel; 15 - wing coverts; 16 - flight feathers of the first order; 17 - khhlup and kochen; 18 - second-order flight feathers; 19 - small braids; 20 - tail feathers; 21 - large braids; 22-23 - tail coverts; 24 - base of the tail; 25 - lower back coverts; 26 - back; 27 - shoulder coverts; 28 - base of the neck; 29 - neck coverts; 30 - neck; 31 - earlobe; 32 - face; 33 - ear; 34 - eye.

A special feature of turkeys is the presence of skin growths called corals on the head and upper neck. Ducks and geese have webbed feet and other structural features.

The entire skeleton is covered with muscles. Muscles attach to bones and cause them to move. This type of muscle is called skeletal muscle. During work, muscles contract and relax, change their shape and length. According to the nature of their activity and the work they perform, they are divided into flexion and extension, elevation and descent, adduction and abduction, locking (sphincters), rotation, etc. The work of the muscular system is often built on the principle of antagonism. So, if there are flexor muscles located on the back surfaces of the limbs, then there are also extensor muscles lying on the front side of the limbs. Their work is strictly synchronized, and if the flexors contract, then at the same time the extensors relax. In total, there are up to 200-250 paired muscles and several unpaired muscles in the body. The combination of skeletal muscles with ligaments, muscle sheaths, blood vessels, nerves and bones forms the meat of the animal.

Peculiar musculature in poultry. It is divided into the red muscles of the legs and the white muscles of the wings and chest. The red color of muscle fibers is given by the protein myoglobin. These muscles differ not only in color, but also in fatigue. Thus, white muscle fibers are stronger, but they fatigue faster than red muscle fibers, while red muscle fibers are less strong, but they fatigue later than white fibers. In relation to carcass weight, muscle tissue in chickens is 42-45%, in ducks - 40-43%, in geese - 48-50% and in turkeys - 52-54%. Birds have a special device - a long tendon cord, with the help of which the toes are locked while the bird is sitting on a tree branch. This adaptation begins at the pelvic fusion as a slender muscle that quickly develops into a long tendon. The tendon passes through the kneecap, then moves to the back of the leg and fuses with the tendon that flexes the toes. When a bird sits on a branch, under the influence of the weight of the body, the knee and ankle-metatarsal joints bend and the bent fingers lock.

The skin protects the bird from exposure to many irritants and is a protective shell. In addition, it is a ventilation device, partially removing carbon dioxide, a number of salts, metabolic products and water from the body. The skin consists of three layers: the epidermis (or cuticle), which covers the outside of the skin, the base of the skin (or skin itself), represented by dense connective tissue, and the subcutaneous layer, which connects the animal's skin to its muscles. The subcutaneous layer is made of loose connective tissue.

The claws, pulps, hooves and hooves, as well as the horns of ruminants, are derivatives of the skin. Skin formations also include sebaceous glands, glands of the eyelids and foreskin, as well as sweat glands, which lie deeper in the skin than the sebaceous glands. In horses and sheep, these glands are found evenly throughout the skin; in cows, a larger number of them are located on the head; in dogs, there are relatively few sweat glands over the entire surface of the body, but there are a lot of them on the soft parts of the limbs. In cats, sweat glands are located only on the soft parts of the limbs.

I. Petrukhin “Home Veterinarian”