Modern horses and related forms of single-hoofed animals belong to the class of mammals, the superorder of ungulates (Ungulata), the order of odd-toed ungulates (Perissodactyla), the family of horses (Equidae), and the genus of horses (Equus). The genus of horses is in turn divided into four subgenera:
1) the subgenus of horses proper (Equus), which includes modern species of domestic horses, a species of wild Przewalski's horse (E. Przewalskii R.), as well as the previously existing tarpan (E. c. Cmelini);
2) subgenus of zebras (E. hippotigris), with species: N. zebra, H. Quagga, N. grevii, etc.;
3) subgenus of donkeys (Asinus) with modern species of African donkeys, common in Africa, Asia and other countries of the world.
Some scientists (V. Gromova) distinguish Asian half-donkeys from the subgenus of donkeys (Asinus) into an independent fourth subgenus (E. Hemionus), which includes modern wild forms: kulans, onagers, kiangs. This was confirmed by hybridization experiments conducted by V. A. Shchekin and A. V. Shkurgin (1933-1950).
In elucidating the history of the evolution of ungulates, the works of the outstanding Russian scientist V. O. Kovalevsky (1842-1883) played a vital role. His monographs on Anchytheria (an ancient representative of equids from the Lower Miocene), on Hyopotamus (from ancient artiodactyls) and other works were of great importance for the development of evolutionary theory and dealt a crushing blow to idealistic views in paleontology about the immutability of species
V. O. Kovalevsky is the founder of modern evolutionary paleontology. In his works on anchytheria (1873), he proved the existence of transitional forms of fossil single-hoofed animals, which Cuvier denied, and formulated the basic laws of evolution of this group of animals.
Anchiterium, according to Kovalevsky, is one of the intermediate genera in the genealogical line of equids. Kovalevsky wrote the following about him: “... anchiterium in the structure of its skeleton is such an intermediate, transitional genus that if the theory of transmutation had not already been firmly substantiated, it could have been one of its most important supports” *.
* (V. O. Kovalevsky, Paleontology of horses, ed. Academy of Sciences of the USSR, 1948, p. 15.)
The works of V. O. Kovalevsky not only clarify the direction and main stages of the evolution of the ancestors of ungulates, but also establish that this evolution was influenced by changed conditions of existence - a gradual transition from a forest lifestyle to life in open spaces.
Adaptation to changing conditions caused a gradual change in the function and structure of animals, especially clearly manifested in the structure of the limbs and dental apparatus.
Life in open spaces and denser soils developed the ability to run quickly and caused the reduction (loss) of the lateral fingers, and the transition to tougher herbaceous food led to changes and complication of the dental apparatus.
The ancestors of horses are found in both Europe and North America, dating back to the earliest layers of the Tertiary period. Due to the fact that North America was connected to Asia by land and many fossil forms were common to both parts of the world, most Soviet scientists consider the evolution of horses in the Tertiary period in general terms, including both forms discovered in Europe and intermediate forms, found in North America.
The conclusion of a number of scientists that the main line of evolution of horses in the Tertiary period took place in North America (where many intermediate forms are known), and only certain genera migrated to Eurasia from America and settled, raises objections, since Tertiary deposits in Asia and Europe are still insufficiently studied; in the future, missing intermediate links can be found here.
The earliest ancestors of the horse were forest animals that lived in tropical rainforests, widespread in the first half of the Tertiary period (in the Eocene and Oligocene) * in the temperate latitudes of the Old and New Worlds. They were adapted to life in the forest on moist and loose soils and fed on lush forest vegetation. The evolution of the most ancient representatives of the horse's ancestors during this period moved towards larger sizes, more complex dental apparatus and the development of the ability to quickly move on loose and viscous forest soil. Simultaneously with the lengthening of the limbs, their adaptation to rectilinear movement occurred, accompanied by strengthening of the trochlear joints and partial reduction of the lateral fingers while maintaining support on three fingers. At the same time, the middle finger acquired large sizes and bore the main load, while the lateral fingers became smaller and shortened, retaining the role of additional support, allowing movement on loose soil.
* (The Tertiary period is the first, most ancient period of the last - Cenozoic - era (the era of mammals and humans). It is divided into five eras: Paleocene (the oldest, which began more than 50 million years ago), Eocene, Oligocene, Miocene and Pliocene. The Pliocene was followed by the Quaternary period.)
The oldest ancestors of equid animals were found in the lower (most ancient) sediments of the Tertiary period of Europe and North America. These animals, belonging to the genus Phenacodus, had five-fingered limbs, resting on three middle splayed fingers, of which the most developed was the middle one, covered with a wide hoof. There was no longer a clavicle in the anterior girdle, the elbow joint was straightened, like in higher single-hoofed animals (this indicates the loss of grasping function and adaptation to rapid movement). The tuberous structure of the teeth indicated their adaptation to soft, juicy plant foods.
One of the species of the genus Phenacodus - tetraclaenodon puercensis S. (from the Lower Eocene), identified by some scientists as an independent genus, is placed at the base of the equine family *.
* (See prof. M. V. Pavlova, Paleozoology, part II, 1929, p. 233.)
The next step in the evolution of equid animals is chiracotherium(Hyracotherium), found in the lower and middle Eocene of Europe and eohippus, who lived in North America during the same period.
Hyracotherium is still a small (30-50 cm) animal with thinner and longer limbs than those of the fenacoda, of which the front ones have four fingers, and the hind ones have three. The traces of the first toe on the front legs have disappeared; on the hind legs, the rudiments of the two outer toes in the form of slate bones have been preserved. The head of Chiracotherium is relatively larger than that of Fenacoda, with an elongated and narrow snout and somewhat more complex, but still typically tuberculate teeth *.
* (See A. Borisyak, Course of paleontology, part II, 1906, p. 297.)
Eohippus had limbs with four toes on the front legs and three on the hind legs and somewhat more complex teeth.
In the Oligocene there lived a form of ancient equids, characterized by further reduction of the digits and some complication of the dental apparatus. It was Mesohippus(Mesohippus), the size of a small shepherd, and a larger one myohippus. Judging by the structure of their teeth, they fed on soft vegetation in the forests; had three-fingered limbs with longer metapodia; spread fingers made it possible to move on loose soil. From the fourth outer toe of the front leg there remains a rudiment of its metacarpal bone; The middle finger was somewhat larger in size than the others, but all three undoubtedly reached the ground. The tail has shortened. The teeth were more complex and stronger than those of Hyracotherium. The complication of the dental apparatus of this form is manifested in the formation of ridges and sockets on the surface of the molars; the premolar teeth are similar in structure to the molars *.
* (See A. S. Romer, Vertebrate Paleontology, translation, ed. L. Sh. Davitashvili. GONTI, 1939.)
At the end of the Oligocene and the beginning of the Miocene, it became widespread in Europe and America. anchytherium(Anchitherium), studied in detail by V. O. Kovalevsky. This rather large animal, reaching the size of a pony, had three-fingered limbs with a more massive and longer middle finger; the outer fingers were shorter and thinner than the middle one, but still reached the ground. Although the teeth of Anchytherium were somewhat more complex than those of previous forms, they still remained low-crowned and did not have constant growth, which indicated the consumption of soft food and life in the forests. According to some scientists, Anchytherium is not in the direct line of horse ancestors.
Studying the dental apparatus of fossil forms of ungulates, V.O. Kovalevsky established that in the middle of the Miocene there was a radical change in the structure of this apparatus, which could only be caused by the transition of ungulates to a new, tougher food. This conclusion was brilliantly confirmed by the work of botanists who established previously unknown herbaceous vegetation in the Miocene *.
* (A. A. Borisyak, V. O. Kovalevsky, his life and scientific works, 1928, p. 110.)
The gradual cooling and decrease in climate humidity entailed changes in vegetation and living conditions for animals. Tropical forests in Europe by the end of the Tertiary period are pushed out of the middle zone to the far south. In their place, coniferous and mixed forests develop in the northern zone, and to the south of these forests - hot savannas and dry steppes. In the Miocene, on the vast plains, herbaceous vegetation developed lushly, which became food and the most important condition for the prosperity of the herbivores that inhabited the plains.
The transition to life in open spaces, with the replacement of soft and succulent forest food by hard and drier grassy ones, caused very important changes in the lifestyle and skeletal structure of equid animals and determined the next decisive stage in their evolution to modern single-hoofed forms. “When the three-toed Anchitherium,” wrote V. O. Kovalevsky, “went to the large dry meadows of the ancient Miocene, then the legs were needed only for support on dry, hard, loose soil; the development of the horse and the predominance of one toe and the Gebiss adaptation began” ( teeth) to herbivory *..."
* (V. O. Kovalevsky, Horse Paleontology, ed. Academy of Sciences of the USSR, 1948, p. 297.)
With the transition to grassy food in the ancestors of horses, as well as in most other ungulates, the dental apparatus becomes more complex, the strength of grinding surfaces increases (the development of folds of enamel and cement), the teeth acquire high crowns and the ability to constantly grow (as they are worn, they move out from the jaw). This compensates for the rapid abrasion of the tooth surface caused by hard herbaceous food, often captured along with soil and sand.
V. O. Kovalevsky shows in fossil turtles how, due to the complication of the dental apparatus, the structure of the jaws also changes, the bones of which became more massive and lengthened, as a result of which the eye socket and cranium moved back during evolution, and the facial part of the skull lengthened.
Life on the open plains developed the ability to run quickly. The denser soil of the plains provides sufficient support for the middle finger, and the side fingers, previously necessary for movement on the loose, viscous soil of the forests, become an unnecessary burden in the new conditions.
During this period, the ancestors of the horse complete the reduction of the lateral toes, and single-hoofed forms with long and slender limbs are formed. The trochlear joints of the legs acquire greater strength as a result of the formation of ridges that fit into the grooves of the opposing bones, which strengthens the joints and protects them from dislocations *.
* (See V. O. Kovalevsky, Horse Paleontology, p. 210.)
This period of evolution is represented by a number of transitional fossil forms.
Remains discovered in the Miocene of North America parahippus(Parahippus) and derived from it merigippusa(Meryhippus) appear to be a transitional form from ancient forest animals to newer forms of animals that lived in open spaces. They were characterized by an even greater reduction of the lateral fingers than their predecessors. Their lateral toes were so shortened that during fast running they probably no longer touched the ground. The teeth were distinguished by a greater complexity of pattern and greater length, but did not yet have constant growth *.
* (See A. S. Romer, Vertebrate Paleontology, 1939.)
In the Upper Miocene and Pliocene of the Old World and North America, the three-toed form of the horse, described under the name hipparion. Hipparion was considered for a long time (including by V.O. Kovalevsky) the direct predecessor of the horse, but later research and discoveries of other forms, closer to the horse, that lived simultaneously with hipparion, forced us to recognize hipparion as a side branch that left no subsequent forms.
In terms of the development of teeth and a more complex and unique pattern of tooth enamel, the hipparion seemed to have overtaken the evolution of the main line of horses of its time, but in terms of the structure of its legs it lagged behind it, retaining primitive three-toed limbs.
Horses modern to Hipparion were already a completely one-toed form with rudimentary bones instead of lateral toes. By the end of the Pliocene, Hipparion became extinct everywhere.
The forms of the main line of mono-ungulates that follow the described ones already show in their skeleton signs of adaptation to life on the plains and the consumption of hard food. These forms stand very close to modern horses. These include the widespread in the Pliocene pliohippus(Pliohippus). This is already a fairly large animal, with even more reduced lateral fingers. Of the lateral fingers of a number of forms, only rudiments in the form of slate-shaped bones remained. The molars had constant growth, were highly crowned, with more complex folds than on the teeth of proto-hippus *.
* (See prof. M. V. Pavlova, Paleozoology, part II, 1929.)
In the Upper Pliocene and in the era transitional from the Pliocene to the Quaternary period *, single-toed forms of ancient horses had already become widespread in the vast steppe territories of Europe, Asia and the continents of North America and Africa then still connected to them by the isthmuses of the continents, often found together with the hipparion. This was a period of increasing cooling and decreasing humidity and climate, characterized by the development of specific steppe flora and fauna in the steppe zone. It was during this period that the hipparion, a resident of the savannas, was replaced by a one-toed horse, a resident of the dry steppes..
* (The Quaternary period consists of the Pleistocene era (beginning about a million years ago) and the modern era. The Pleistocene, in turn, is divided by individual scientists into lower (the most ancient), middle and upper. The earliest epoch of the Quaternary period (transitional from the Tertiary) is also distinguished, called the Post-Pliocene.)
Ancient horses of the Upper Pliocene, the remains of which were found in many places in Europe, Asia, Africa, America, including on the Azov coast (Rütimeyer, V. Gromov, etc.), although they already had completely one-toed limbs, were still different from modern ones horses have a number of significant characteristics, in particular a more narrow-browed and long-muzzled shape of the skull, a more folded structure and smaller teeth and thin bones of long limbs.
This widespread form, the European and African remains of which are described under the name " horses Stenopa", was the progenitor of later forms (in America, representatives of a similar form are described under the name E. Plesippus).
The Pliocene Stenon horse was found in two varieties: a smaller, typical form - E. Stenonis tipicus and a larger one, approaching in height the largest heavy horses, but light in build and thin-legged, which is described under the name E. Stenonis major *.
* (See V. Gromova, Experience in studying the process of formation of forms in mammals (genus Equus horse). Proceedings of the Zoological Institute of the USSR Academy of Sciences, vol. VI, no. 4, 1941, p. 124.)
Close in composition to E. Stenonis was the Pliocene horse of China E. Sanmeniensis, as well as the form E. sivalensis found in India.
One of the best known and best studied is the phylogenetic series of modern single-toed ungulates. Multiple paleontological finds and identified transitional forms create a scientific evidence base for this series. The phylogenetic series of the horse, described by the Russian biologist Vladimir Onufrievich Kovalevsky back in 1873, remains an “icon” of evolutionary paleontology today.
Evolution through the centuries
In evolution, phylogenetic series are successively successive transitional forms that led to the formation of modern species. Based on the number of links, the series can be complete or partial, but the presence of successive transitional forms is a prerequisite for their description.
The phylogenetic series of the horse is considered evidence of evolution precisely due to the presence of such sequential forms that replace each other. The multiplicity of paleontological finds gives it a high degree of reliability.
Examples of phylogenetic series
The row of horses is not the only one among the examples described. The phylogenetic series of whales and birds has been well studied and has a high degree of reliability. And controversial in scientific circles and most used in various populist insinuations is the phylogenetic series of modern chimpanzees and humans. Disputes regarding the missing intermediate links here do not subside in the scientific community. But no matter how many points of view there are, the importance of phylogenetic series as evidence of the evolutionary adaptability of organisms to changing environmental conditions remains indisputable.
The connection between the evolution of horses and the environment
Multiple studies by paleontologists have confirmed the theory of O. V. Kovalevsky about the close relationship of changes in the skeleton of the ancestors of horses with changes in the environment. The changing climate led to a decrease in forest areas, and the ancestors of modern single-toed ungulates adapted to living conditions in the steppes. The need for rapid movement provoked modifications in the structure and number of fingers on the limbs, changes in the skeleton and teeth.
The first link in the chain
In the early Eocene, more than 65 million years ago, lived the first ancestor of the modern horse. This is a “low horse” or Eohippus, which was the size of a dog (up to 30 cm), rested on the entire foot of the limb, which had four (front) and three (back) fingers with small hooves. Eohippus fed on shoots and leaves and had tuberculate teeth. Brown coloring and sparse hair on a mobile tail - this is the distant ancestor of horses and zebras on Earth.
Intermediates
About 25 million years ago, the climate on the planet changed, and steppe expanses began to replace forests. In the Miocene (20 million years ago), mesohippus and parahippus appeared, more similar to modern horses. And the first herbivorous ancestor in the phylogenetic series of the horse is considered to be Merikhippus and Pliohippus, which entered the arena of life 2 million years ago. Hipparion - the last three-fingered link
This ancestor lived in the Miocene and Pliocene on the plains of North America, Asia and Africa. This three-toed horse, resembling a gazelle, did not yet have hooves, but could run fast, ate grass, and it was she who occupied vast territories.
One-toed horse - pliohyppus
These one-toed representatives appear 5 million years ago in the same territories as hipparions. Environmental conditions are changing - they are becoming even drier, and the steppes are expanding significantly. This is where single-fingeredness turned out to be a more important sign for survival. These horses were up to 1.2 meters high at the withers, had 19 pairs of ribs and strong leg muscles. Their teeth acquire long crowns and folds of enamel with a developed cement layer.
A familiar horse
The modern horse, as the final stage of the phylogenetic series, appeared at the end of the Neogene, and at the end of the last ice age (about 10 thousand years ago), millions of wild horses were already grazing in Europe and Asia. Although the efforts of primitive hunters and the reduction of pastures made the wild horse a rarity already 4 thousand years ago. But two of its subspecies - the tarpan in Russia and the Przewalski's horse in Mongolia - managed to last much longer than all the others.
Wild horses
Today there are practically no real wild horses left. The Russian tarpan is considered an extinct species, and the Przewalski's horse does not occur in natural conditions. Herds of horses that graze freely are wild domesticated forms. Although such horses quickly return to wild life, they still differ from truly wild horses.
They have long manes and tails and are of different colors. Exclusively dun Przewalski's horses and mousey tarpans have trimmed bangs, manes and tails.
In Central and North America, wild horses were completely exterminated by the Indians and appeared there only after the arrival of Europeans in the 15th century. The feral descendants of the conquistadors' horses gave rise to numerous herds of mustangs, the numbers of which today are controlled by shooting.
In addition to mustangs, there are two species of wild island ponies in North America - on Assateague and Sable Islands. Semi-wild herds of Camargue horses are found in the south of France. Some wild ponies can also be found in the mountains and moors of Britain.
Our favorite horses
Man tamed the horse and bred more than 300 of its breeds. From heavyweights to miniature ponies and handsome racing horses. About 50 breeds of horses are bred in Russia. The most famous of them is the Oryol trotter. Exclusively white coat, excellent trot and agility - these qualities were so valued by Count Orlov, who is considered the founder of this breed.
A horse is a large animal that moves on four limbs. The front pair of limbs bears 65% of the load, while the hind limbs bear only 35%. During the process of evolution, the structure of the forelimbs of horses has undergone changes. The forelimbs now allow the horse to move quickly over difficult terrain and can withstand considerable strain. In this article we will look at the structure of the horse's forelimbs, their evolution, the mechanism of operation and common diseases of the limbs and hooves.
The ancestor of modern horses, Orohippus, had long, four-toed paws, each toe ending in small hooves. He did not know how to move quickly and hid from predators in mountainous areas, climbing steep slopes. His hooves began to harden, his middle fingers began to develop for better traction with the soil. The lateral fingers of Orohippus, on the contrary, shrank, moved higher and turned into rudiments. In modern horses, these toes are present in the form of thin subcutaneous bones on either side of the hoof.
Orohippus began to walk on the tips of its middle toes, thereby stimulating the development of its hooves. Along with the growth of its hooves, its speed also increased, and it migrated to steppe regions rich in plant food.
Important! If the foal's vestigial toes are overdeveloped, they must be removed so that the animal does not experience discomfort while running as an adult.
The structure of the forelimb of a horse
The forelimb of a horse is a complex system consisting of bones and muscles, which is designed to bear heavy loads and allows the animal to move quickly and maneuverably. 
The scapula is the flat base of the shoulder and is connected to the humerus through the shoulder joint. It is located just below the line where the withers and neck meet and is connected to the neck and spinal column through the collarbone.
The length of the shoulder blade affects the working qualities of the animal. Heavy draft horses have low withers and correspondingly small shoulder blades. This skeletal structure provides greater stability. 
Saddle horses have high withers and a long shoulder blade with a small angle between it and the humerus. The longer the shoulder blade and the smaller the angle of its inclination relative to the shoulder, the more elastic the animal’s movement and the wider its step. Depending on the angle of inclination, the scapula can be steep (large angle), oblique (small angle) and medium (normal angle). A developed long shoulder blade lengthens the front part of the body, which is typical for racehorses.
Did you know? The most sensitive parts of a horse's body are its lips and hooves! Despite their hardness, the hooves are riddled with nerve endings and blood capillaries. The horse seems to feel the road with them when it walks along it, and carries its rider in the safest way. Plus the horse's hooves- this is its most effective weapon. A strike from a shod hoof is considered incredibly painful, while an unshod hoof is more likely to kill an opponent than injure it.
Elbow
A well-muscled, developed elbow at rest should be tightly pressed to the animal’s chest. If the elbow is set to the side or sagging, it means that the horse’s chest and limbs are poorly developed, and such an animal will not be able to work.
Forearm
Connected to the elbow through cartilage. Mobile and long, assembled from the ulna and radius bones. At the level of the forearm there are important extensor muscles that move the metacarpus, so the forearm should be muscular and long. This limb structure gives the animal a smooth, sweeping step. 
Wrist
This is a complex structure that consists of seven bones. The wrist should be wide, dry, and clearly stand out above the metacarpus. The skin on a healthy wrist is stretched smooth and thin. When viewed from the front, the carpal bones should be symmetrical and rounded.
Important! Swelling of the skin on the wrist and the abundance of connective tissue on it indicate developing internal inflammation. Inflammation most often indicates a tendon strain, in which case you need to immediately begin treatment.
Fetlock and pasterns
The pastern is a spring mechanism that, together with the fetlock joint, softens the impulse from the hoof hitting the ground. The grandmother should be straight, not clubfooted. When viewed from the side, you will notice the angle of inclination of the headstock to the ground, which is normally 60°. The pastern is connected by cartilage to the fetlock joints and the hoof. 
The fetlock joints of healthy individuals are dry, sinewy and strong, with a skin swelling on the inside covering small sesame bones. These bones protect the fetlock joint from sagging. As horses grow older, hard guard hair brushes grow on their fetters, which protect the skin and tendons from injury.
Did you know? The Maasai people revered horses as sacred animals. It was believed that a member of the Maasai tribe, killed by a horse's blow, was immediately transported to heaven. The Mordvins also did not lag behind the Masai- their respect for horses was so great that women could ride these animals only by wearing two skirts at once. It was believed that a woman could desecrate a sacred animal by touching her feet.
Pastern
Consists of two bones - metacarpal and slate. The pastern should be short, smooth and wide, with pronounced tendons. Based on the examination of the pastern, the strength of the horse's legs is assessed. 
Corolla and hoof
At the base of the hoof there are three bones: the navicular, coronoid, and ungulate. The meat corolla is located above the coronary bone and is responsible for the blood supply to the hoof.
The hoof on the horse's front limb is wider than on the hind limb. The surface of the hoof is flat, with a large frog (the indentation on the sole of the hoof), and a low heel bone. The darker the color of the hoof, the stronger it is. 
What happens to a horse's limbs when running
Horses' joints act like door hinges and only extend in one direction. During the step, the hoof hits the ground. The pastern and fetlock soften this blow, absorb it through the tendons and transmit it further to the metacarpus and wrist. The wrist bends for the next step, the muscles transfer the impulse higher to the forearm, shoulder and shoulder blade.
Important! The faster the animal moves, the more intense its blood circulation, the better developed and lubricated the joint capsules. A horse that moves little and slowly suffers from rheumatism, swelling and problems with blood supply to the limbs.
There are several types of natural gaits for horses. These are walk, trot, gallop and amble. These species differ in the pace of movement and the order of throwing their limbs. The most familiar and simplest gait for a horse is a step in which the support is made alternately on two or three limbs. The most difficult one is ambling, it is characteristic of some wild horses; it is very difficult to train an animal in this gait. An animal ambling steps first on the left fore and hind limbs, and then on the right fore and hind limbs.
Diseases of limbs and hooves in horses
Trained healthy limbs are the key to productive and successful work of the animal. Most diseases of equine limbs occur due to improper care and poor living conditions.
Brockdown
The most common disease in riding horses. Occurs due to partial rupture of the flexor tendons. One or two tendons on the metatarsus or metacarpus may be damaged. The longer the pastern and pastern, the higher the risk of buckdown. In addition to overload, rockdown can be caused by too tight bandaging of the metacarpus and hereditary disposition. 
To eliminate the rockdown, for the first two days, ice compresses are applied to the damaged tendons, the general anti-inflammatory drug Phenylbutazone is administered intravenously, and local corticosteroids such as Dexamethasone are used.
Did you know? The right to be called the smallest horse in the world belongs to an animal named Thumbelina. In 2006, this baby was included in the Guinness Book of Records. Her height at the withers is 43 cm, and her weight- 25 kg. The smallest foal in the world is considered to be a baby named Einstein. He belongs to the Pinto breed and weighed only 2.5 kilograms at birth.
Rheumatism of the joint
This is extensive damage to the collagen tissue of cartilage by streptococcal bacteria. A rheumatic attack is preceded by acute pain that lasts from twelve hours to a day. The condition for the appearance of rheumatism is keeping in damp rooms, sudden changes in temperature after physical activity. 
A horse suffering from rheumatism holds the affected limb suspended and scrapes the bedding with it. Upon examination and palpation, swelling and increased temperature at the site of the lesion can be detected. Most often the hocks are affected, less often the knee joints. If you do not resort to treatment, the cartilage will increase five times in a day, and lymph may appear on the skin. Treatment of an acute attack is carried out by intramuscular injection of 15 ml of Diclofenac or Reopirin.
Important! To increase the effectiveness of treatment and shorten the recovery period, it is necessary to wrap the sore joints warmly after injections and, if possible, place warm heating pads on them.
Swelling (fulling) of the joints
It is a soft thickening in the joint area. The horse does not feel discomfort when it appears. The reason for its appearance is a sedentary lifestyle, imposition of fetters, disproportionate loads in young animals, bruises. The best way to prevent flooding is to walk animals at least four times a day and limit exercise. 
Calluses
They occur due to excessive pressure on the hoof, a pebble stuck in the hoof tissue, or a broken horseshoe that has not been changed for a long time. It looks like a keratinized, discolored thickening.
If you find a callus on a horse, the horseshoe must be immediately removed, the callus must be carefully cut out, and an alcohol poultice applied to the damaged area. To prevent calluses, you need to regularly inspect and clean your hooves.
Did you know? The most common horse name in the world is Zhu Han, which translated from Chinese means “go to the owner.” China has the largest number of horses compared to other countries. Perhaps this is what explains the popularity of this name.
Laminitis
The second name for this disease is opoi. This is an inflammation of the thin sheet layer (lamina) connecting the coffin bone to the horn. With laminitis, the sheet layer is not supplied with blood, its tissue begins to die and increase in size. A horse with laminitis places his hoof on his heel and immediately lifts it. The local temperature of the hoof rises, the arteries above the fetlock joint pulsate rapidly. 
First of all, it is necessary to restore blood circulation in the hoof, for which nitroglycerin lotions are applied to the corolla area. During the recovery period, the animal is walked on damp, cold sand and given regular injections of drugs that improve blood circulation, such as Heparin and Isoxsuprin.
Scaphoid
The cause of disease of this bone is excessive load or incorrect constitution of the hoof walls. Only the forelimbs are affected by this disease. 
The horse begins to limp, kneeling and arching the front of the hoof toward the ground to relieve pressure on the painful area. There are special orthopedic horseshoes, the installation of which will reduce the load on the scaphoid bone and eliminate pain.
Important! During the period of breaking in new horseshoes, the horse must be injected intramuscularly with local anti-inflammatory drugs. An animal that continues to experience bone pain will put on its hoovesall the sameincorrectly, and the reforging efficiency will be zero.
Osteitis
This is inflammation, and then suppuration of the coffin bone, which is a consequence of laminitis. It occurs due to demineralization of hoof tissues and frequent shocks. The animal develops a shuffling gait, shifting the load from the front hooves to the hind hooves. The infected hoof must be cleaned, disinfected and alcohol lotions placed under clean bandages twice a day.
Classification
The modern horse belongs to the equine family, which also includes zebras and donkeys. The Equidae family, together with rhinoceroses and tapirs, belong to the order Odd-toed ungulates and are descendants of Condylarthra, from which all ungulates originated. The Condylarthra group are dog-like animals with five-toed, padded limbs, long extinct primitive mammals of an ancient Paleocene group.
Scientists have learned how the horse evolved 60 million years ago and how it gradually adapted to changing environmental conditions through the study of fossils.
At this time they looked completely different from a horse and looked more like a dinosaur. The most ancient ancestor of the horse, the remains of which have survived to us, is barylambda. She was quite thick, more than two meters long, her legs were short and ended in five toes with nails that vaguely resembled a hoof. Barylambda fed on grass and small shrubs.
55 million years ago there was a continent that can be called Euroamerica. At that time, modern Europe and North America were not yet separated by the Atlantic Ocean, and they were separated from Asia by a sea strait that ran where the Ural ridge is now located. It was a prosperous continent, with a tropical climate, covered with evergreen forests. The air was full of thick, intoxicating vapors, and the earth grew a rich harvest of bushes, vines and tropical giant trees, their trunks reaching far into the air. Where sunbeams made their way through the dense canopy of the tropical forest, in the forest clearings lived unusual, dog-sized mammals that fed on the foliage of shrubs and soft forest grasses - Hyracotherium, or Eohippus (from the Latin “horses of the dawn”).
They had a small head on a short neck, a long body and short legs. Eohippus had four toes on the front legs, and three toes on the hind legs. Small teeth with low crowns were adapted for chewing only juicy soft leaves and small invertebrates. The weakness of the masticatory system was also confirmed by the short facial region. The eye sockets were located in the middle of the skull. This creature's legs were bent and low. When walking, Eohippus rested on the pads of its toes, each of which ended in a claw (future hooves). When moving, the animal resembled a modern dog. It is clear that with such legs it was impossible to compete in speed with fleet-footed predators in open spaces, so Eohippus hid in the thicket of the forest, thickets of bushes and was “dressed” in a skin with short and sparse hair, striped or spotted in color, like modern forest and savannah animals.
45 million years ago there lived small horses, less than half a meter tall - Orogippus.
The small manes on the necks of these horses were motionless, but their tails, overgrown with sparse hair, fluttered in the air. Their fur was dun in color, decorated with several inconspicuous longitudinal light stripes. The front legs of orohippus were still four-toed, and the hind legs were three-toed, and all the toes had small hooves. But already in these primitive horses, the bones of the middle toes were more developed than the lateral toes.
The climate changes - the horses change
The remains of Mesohippus, which flourished in the Oligocene era, indicate significant changes in the species: the legs became longer, the back straightened (Eohippus had a concave back), and the size of the animals became larger. One toe disappeared from the front legs, and all four legs became three-toed. The teeth have also changed, the small molars are almost equal to the large ones.
In the Miocene, an event occurred that significantly influenced the development of equine forms. The climate on the planet became more continental, winter and summer became much more distinct, and the tropics retreated to the equator: treeless spaces began to appear. Since there were fewer forests, some of the animals were forced to settle in treeless spaces, and having settled on them, they were forced to somehow adapt to new conditions. Around this time, the three-fingered Myohippus, Parahippus, Merikhippus and Anchytherium appear.
“When three-toed anchytheria went to the large dry meadows of the ancient Miocene, then only legs were needed for support on dry, hard, inviscid soil; the development of the horse and the predominance of one toe began...” wrote the Russian scientist Vladimir Onufrievich Kovalevsky, to whom the world owes knowledge history of the modern horse. However, this did not happen immediately. In the new conditions, the legs of the ancient horses became longer, and now the animals could cross large spaces in search of fresh and safe pastures.
Anchytherium was replaced by Hipparion, a small three-toed horse about the size of a donkey, the remains of which usually predominate over other fossils. For the first time among horses, his teeth are found to be adapted for eating herbs. The surface of this animal's teeth is covered with complex enamel loops that prevented them from abrasion when eating hard food. At the same time, the teeth of the hipparion still had a lower crown than those of the horse, and, therefore, were suitable for abrading not very hard food. The structure of the limbs of hipparions suggests that they were adapted for movement on soft swamp soils. The hipparion's legs could bend at a sharper angle than those of a horse, just like those of reindeer and elk, and thus rose much higher when walking and running, which allowed it to easily move through tall grass and hummocky swamps.
Hipparion represents, according to some new research, a lateral branch, now extinct, although in some areas it even existed simultaneously with real horses. Hipparion was replaced 2–3 million years ago by the one-toed horse, which arose from the closely related genus Pliohyppus, which was better adapted to living conditions in the steppes and spread from North America to all continents.
Pliohippus were quite large, reaching approximately 120 cm at the withers, and, unlike their predecessors, Eohippus, they lived in dry steppes. The hooves on the middle toes of pliohyppus became increasingly larger and wider. They held animals well on solid ground, gave them the opportunity to tear apart the snow in order to extract food from under it, to protect themselves from predators, while the lateral fingers, on the contrary, constantly became smaller during evolution, shortened so that they no longer touched the ground, although they were still clearly visible, and in the end were preserved only in the form of small, rod-like bones just under the skin.
This change in the limbs during the evolution of the horse is due to the fact that the descendants of primitive horses more and more often moved from swampy and swampy forests to the solid soil of dry steppes overgrown with grass and shrubs. While for the earliest ancestors of horses, a greater number of toes on the limbs was justified, since it gave them greater safety when walking on soft, marshy soil, life in changed conditions made it more advantageous for their side toes to gradually die off, and the middle toes to develop, because in the steppe the soil is strong, hard, suitable not only for safe walking, but also for a rapid gallop. Fast movement was vital for pliohippus, as it served as their only defense against attack by predators.
A million years ago the real Equus appeared
During the Pleistocene and Ice Ages, Equus, the ancestor of the modern horse, migrated to Europe, Asia and Africa along the isthmuses that existed at that time between the continents. Subsequently, about ten thousand years ago, with the end of glaciation, these isthmuses (in their place are now the Straits of Gibraltar and Bering) disappeared, and this meant that animals that had become extinct on one of the continents could no longer repopulate it - at least without human help. This is exactly what happened in America: for some unknown reason, horses disappeared there. All members of the modern family Equidae are excellent runners and have one functional toe on each foot (the vestigial toes of the modern horse - bony growths on the back of the fetlock joint - apparently only a reminder of the structure of the foot of Eohippus). All of them lead a gregarious lifestyle, and all of them have molars adapted for grinding herbaceous food.
Every modern horse and pony, by all characteristics, traces its ancestry to one of three types, formed in different climatic conditions. Northern Europe was the birthplace of the heavy, slow-moving horse (Equus silvaticus), from which all known heavyweight breeds originate. In addition to it, there was a primitive wild horse in Asia, specimens of which were discovered in 1881 (Przewalski's horse); and in Eastern Europe lived more graceful tarpans.
It took many centuries before a living creature, in its amazing development, went from a small eohippus to a modern horse - our most noble animal and man’s faithful assistant. Between them is a whole series of ancient horses - from a five-toed horse the size of a fox to the European tarpan.
Look at the photographs showing the three ancestral forms of the modern horse. Arrange these elements in the sequence in which the evolutionary changes of the leg took place.
1. Write down in the table the corresponding sequence of numbers that indicate the photographs.
2. Using knowledge of the physiology of movement, explain why the evolution of the horse followed the path of reducing the number of toes.
Explanation.
1. Having studied the causes of the evolutionary process using the example of a horse, O. Kovalevsky (1842-1883) concluded that changes in its structure are associated with changes in its habitat. With climate change, forest areas decreased, and the increase in open steppe spaces contributed to changes in the living environment of the ancestors of horses. They began to adapt to the conditions of the steppes. To escape from enemies and find pastures with rich vegetation, it was necessary to learn to run quickly. Movement over long distances contributed to a change in the number of fingers on the limbs. Not only the limbs underwent changes, but also the shape of the body, skull, and structure of the teeth - due to chewing grass. A complete restructuring of the horse's body took place. Such changes were: a decrease in the number of fingers from five to one, strengthening of the body, and complication of the molars. All this indicates the process of evolution of the horse.
V. O. Kovalevsky studied the evolution of modern horses and named the stages of their development with the names of the centuries of the Tertiary period of the Cenozoic era. The horses were arranged according to the decrease in the number of toes on the limb.
1. Phenacodus (existed in the Paleocene), five-toed, the size of a fox.
2. Eohippus (lived in the Eocene), height 30 cm, with four-toed forelimbs, three-toed hind limbs.
3. Myohippus (lived in the Miocene), the middle finger is well developed, the second and fourth fingers are short.
4. Parahippus (lived in the Miocene), the middle finger is highly developed, the second and fourth fingers are shortened.
5. Pliohippus (existed in the Pliocene), one-fingered, the remaining fingers are atrophied.
6. Modern horse.
The discovery by V. O. Kovalevsky of a systematic series in the study of fossil horse species is a typical example of an evolutionary process. The presence of successively replacing each other makes it possible to construct a series with a high degree of reliability of evolution, which is called phylogenetic.
Answer: 312.
2. The smaller the point of contact with the surface, the faster the speed of movement. When we walk, we rely on our full foot, and when we run, we rely only on our toes. The horse became one-toed, because in the steppe expanses one-toed gave advantages in speed of movement.
Answer: The smaller the point of contact with the surface, the faster the speed of movement.
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