...th and South America in a ave of extinctions that occurred near the end of the Pleistocene Epoch, about 15,000 years ago. They ere not seen in the Americas again until 1494, hen Italian explorer Christopher Columbus transported them on ships from Spain on his second voyage to the Ne orld.Przealskis horse, hich is believed to be the only truly ild horse to survive to modern times, probably became extinct in the ild in Mongolia in the 1960s. About 1,100 Przealskis horses survive today in captivity in zoos and ildlife parks.IIPHYSICAL CHARACTERISTICS As a result of deliberate breeding by humans, horses display a remarkable variation in size, body shape, and coat color. Traditionally, a horses size is measured at the ithersan elevated part of the spine beteen the neck and the back. The measurement is made in hands one hand equals about 10 cm 4 in. Typical riding horses stand 14 to 16 hands high and eigh 400 to 500 kg 900 to 1,100 lb. The smallest horse on record, a Falabella miniature pony, stood 48 cm 19 in, or just under 5 hands, and eighed 14 kg 30 lb. The largest horse on record as a Belgian that stood 1.8 m 6 ft tall, or 18 hands, and eighed 1,450 kg 3,200 lb. The horse has a hairy coat and a long mane and tail. A heavy inter coat gros in the fall and sheds in the spring. Typical coat colors include black, bron, gray, cream, gold, and hite. The mane and tail can be the same or different from the body color, and many variations in color can result from inherited traits that cause spotting, dilution of the basic coat colors, or a sprinkling of hite hairs in the coat. Many color patterns have specific names, such as bay bron ith black mane and tail, chestnut reddish bron ith mane and tail of the same or lighter color, and palomino gold ith a creamy hite mane and tail. A horses head is composed of the cranium, hich encloses the animals large, complex brain, and the face, distinguished by a long muzzle consisting of the nose and lips. The muzzle provides enough distance beteen the horses mouth and its eyes so that it can graze and atch for danger at the same time. Horses have the largest eyes of any land mammal. The large eyes protrude from the sides of the head, enabling horses to see almost directly behind themselves, even hile facing forard. Their night vision is excellent. Horses have limited color vision, hich appears to be similar to one of the less common forms of color blindness in humansthey perceive red and blue, but they cannot distinguish beteen green and shades of gray.Horses have poerful teeth and jas to grind and break don plant fibers. Their teeth gro continuously as their surfaces ear don. Male horses usually have 40 teeth and females have 36. Beteen the front incisors and the rear molars is a gap called the diastema, here the bit is placed. Horses can close their ide nostrils against dusty inds, and they can move their large ears to detect sounds from various directions.A horses head is held up by its long, flexible neck, hich lets the horse reach don to the ground to feed, rise to a high vantage point to sight danger, and bite itches on the front part of its body. The horses body has a ide chest, hich holds its enormous lungs and heart and a muscular back, beneath hich lie the horses internal organs for digesting food and reproducing. A horses long, floing tail helps keep its hindquarters arm and is used to sish aay insects. The specialized structures of the horses legs make the animal a very efficient runner. hat e think of as the horses knee is actually the equivalent of a humans ankle, so from the knee don the leg is really a highly elongated foot. The loest part of the foot is the tip of a single toe, hich corresponds to the tip of a persons middle toe. This large, strong toe tip is ell protected by a tough, curved hoof. By standing on its toes, the horse has a very long leg for an animal of its size, but also a very light leg, since toes are lighteight structures, carrying a minimum of bone and tendon and no muscle at all. Like a persons foot, a horses foot has a sole. In the horse, the sole includes a rubbery, V-shaped structure called the frog, hich helps absorb the impact of the foot against the ground.Many of the joints in horses legs are comparable to hinges that permit forard and backard motion only. This type of joint requires feer muscles than are needed for the kind of ball-and-socket joint that occurs in the human hip, hich can rotate in any direction. This yields a further savings in eight. Long, light legs allo a horse to move very efficiently. A long leg produces a long stride, and a light leg allos the horse to sing its limbs back and forth quickly ith a minimal expenditure of energy. The top speed of the horse is about 70 kmh 45 mph.AInternal Organs The horse has very efficient respiratory and circulatory systems that enable it to race at high speeds ithout running short of air. hile alking, a horse consumes only 1 liter about 0.25 gallon of oxygen a minute, but at a racing gallop, its oxygen consumption can approach 60 liters nearly 15 gallons per minute. At the gallop, the horses head and neck move up and don in rhythm ith each stride. This motion tends to squeeze and expand the lungs, so that a galloping horse automatically takes exactly one breath per stride. This mechanism ensures that the faster the horse gallops, the more air it takes in.The horse has a single stomach and a large digestive organ called the cecum, hich forms a dead-end alley at the junction of the large and small intestines. Microorganisms that live in the cecum break don cellulose, a tough substance ithin the alls of plant cells, making it possible for the horse to digest grasses. The cecum has a comparable role to the rumen, a specialized stomach chamber present in ruminants, or cud-cheing animals, such as cos and sheep. Horses cannot extract as much energy out of food as ruminants do, but they are able to digest food more quickly. As a result, a horse can eat more food each day than a co of the same size. Due to this difference, horses can survive on stemmy, high-fiber roughage that ould not sustain a co. IIIREPRODUCTION Horses reach sexual maturity at about one and a half years. The estrous cycle in the marea mature female horsetypically lasts 21 days. During the first five days of the cycle, the mare is usually receptive to mating. The estrous cycle stops during inter and resumes in the spring, hich is the start of the breeding season. A stalliona mature male horseapproaching a mare in estrus engages in various courtship rituals. These include uttering nickering sounds and sniffing and licking the mares genital area.The gestational period in the horse averages 11 months. Mares generally give birth to a single offspring, or on rare occasions, tins. Young horses that have not yet been eaned are called foals. Young female horses are called fillies, and young males are called colts. Among feral horses, stallions guard a harem of mares and compete ith other sta...
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