Knowing the parts of the horse, as well as the internal framework, assures a better understanding of the horse’s biology and, therefore, its care. Furthermore, knowing the horse part names as we call them here is necessary to better understand the teachings in other sections of this school site.
HORSE PARTS
Barrel
BARREL (or MIDDLE SECTION): This is the largest section of the horse’s
body that includes the withers, back, loin, shoulders, chest, thorax, ventral edge,
girth area, abdomen, inguinal region, and flanksBARREL (or MIDDLE SECTION): This is the largest section of the horse’s
body that includes the withers, back, loin, shoulders, chest, thorax, ventral edge,
girth area, abdomen, inguinal region, and flanks.
HEAD
HEAD: When viewed from the side, the horse’s head has the shape of a big
hammer. In contrast to the rest of the horse’s skeleton, the cranial cavity is formed
by several small, semi-flat bones that contain and protect the horse’s brain.
NECK
NECK: The horse’s head is connected to the barrel by means of the neck. One of
the main functions of the neck is to lower the horse’s head until the horse’s lips
and incisors are able to reach the grass on the ground.
HIPS
HIPS: The hips are located behind the loin, in front of the tail, and above the hind
legs. The bone structure of the hip is formed by the “sacrum” and the pelvic girdle
(ilium, ischium, and pubis). Hips have a big muscle mass around the bones,
making them a good place to give intramuscular injections.
TAILS
TAIL: The tail is located behind the sacrum and projects downward. The tail is
formed by the coccygeal vertebrae, many tendons (that provide great mobility),
veins, arterioles, nerves, and skin. Many long hairs (known as the “tail’s skirt”),
similar to those of the mane, grow out of the lateral and the upper surfaces of the
tail, which give the horse beauty and grace.
LEGS
LEGS: The horse is a quadruped, which allows it to reach high speeds when
running. The two front legs, or forelegs, sustain from 55% to 60% of the body
weight, and their main function is for support. The two rear legs, or hind legs,
sustain the remaining 40% to 45% of the body weight. The other function of the
hind legs is propulsion.
- HEAD: When viewed from the side, the horse’s head has the shape of a big hammer. In contrast to the rest of the horse’s skeleton, the cranial cavity is formed by several small, semi-flat bones that contain and protect the horse’s brain.
Each one of the two small ears is erect and shaped like half of an empty cone with the point at the top; the wide bottom joins the top of the head. Each ear may be rotated toward the front, the side, or the back, allowing the horse to locate the direction of the origin of a sound. Movements of the ears are also used by horses to communicate with other horses, as part of a complex body language. The ears are covered by skin and hair of the same kind and color as the coat, although the edges may be darker on horses with black factor color. The hardest structure of the ears is the cartilage.
The top edge of the forehead is defined by the ears, and its lower edge is defined by the eyes. If a horse has a large, flat forehead, this is considered by some to be a sign of intelligence because it appears to provide more room for the brain, although it has not been proven.
The horse’s two big eyes are located on each side of the head, just at the corners of the lower edge of the forehead. Each eye occupies one orbital cavity. The strategic placement of the eyes allows the horse to have a binocular field of vision of about 65 degrees toward the front. In addition, each eye has a large monocular field of vision, toward the sides, almost reaching behind the head. 2 inches above each eye, there is a small oval groove called the “temporal fossa.”
The horse’s face (front profile and cheeks) is located below the eyes. The face is only supported by the nasal and the maxillary bones, covered by very thin muscles and skin. When the horse suffers “big head disease” due to an excess of phosphorus in its diet for an extended period of time, the maxillary bones become weak and rounded out toward the cheeks. The muzzle is the bottom of the head, formed by the nostrils, upper and lower lips, and the chin.
The nostrils are two oval holes located below the face at the front lower corners of the muzzle. Although a horse’s nostrils will dilate during exercise, large nostrils are better than small ones because they are the primary entry way of fresh air to the respiratory system.
The lips, upper and lower, have great mobility, pressure ability, and sense of touch (comparable to a person’s hand). They allow the horse to select food before introducing it to the mouth. When a horse is not eating, its lower lip should be closed firmly against the upper one. The point where the upper and lower lips join at each side is called the “corner of the mouth.” The chin is the fleshy and rounded prominence located behind/below the lower lip.
The horse’s teeth have different functions in the mouth. They are located in the sockets of the maxillary and mandible bones, supported firmly by the gums. The function of the incisors, located at the front of the mouth and covered by the lips, is to cut grass from the pasture and to bite while fighting. Premolars and molars, located above the corners of the mouth, chew food. Canines are located in the interdental spaces between the incisors and premolars in males over four years old; however, canines have no purpose for the modern horse.
The tongue is a relatively big muscular organ in the horse. Its function is to taste food and to carry it from the front part of the mouth to the premolars and the molars located in the back for chewing. The tongue also allows swallowing.
Chewing food is accomplished by the movement of the mandible (or lower jaw), of which both upper ends join with the temporal bones. The masseter muscles, and other facial muscles, produce the chewing motion. The mandible has two branches (bones) starting above each side of the masseteric region, which are projected downward and fused in the chin area. These two bones of the mandible may fracture above the chin area if the horse pulls forcefully while tied with a poorly designed halter or similar piece of tack which straps, cords, or ropes around the muzzle area become tighter as the horse pulls (mostrar imagen)
- NECK: The horse’s head is connected to the barrel by means of the neck. One of the main functions of the neck is to lower the horse’s head until the horse’s lips and incisors are able to reach the grass on the ground. Additionally, the horse uses its neck and head together to provide optimal balance during locomotion. Regions of the neck include the poll, crest (upper edge), lower edge, sides of the neck, and jugular groove.
The poll unites the head with the neck, just behind the ears. The joint between the occipital bone (rear of head) and the atlas (first vertebrae) allows the head to move up and down. The joint between the atlas and the axis (second vertebrae) allows the head to move from side to side. In addition to the atlas and axis, the neck has five other cervical vertebrae, which allow the neck to move in different directions.
More than twenty pairs of muscles control neck movements. This abundance of muscles provides a good location for intramuscular injections in both sides of the neck. With age, the neck’s crest of some horses starts to fall to one side (known as “fallen crest”), which is increased/anticipated when horses have been fed in feeders placed above the ground level for several years.
Hypothyroidism may also result in a big crest that falls to one side as the horse ages. However, a horse having a fallen crest does not necessary mean it has a thyroid problem, for which it must be properly tested to confirm. Furthermore, in some horse breeds there has been a selection for decades looking for thick and arched necks as the ideal conformation; this has led that some specimens end with a fallen crest as they age, which worsens when having been fed for long time above ground level as mentioned above.
Numerous long hairs, called the mane, grow in the neck’s crest. When the mane is well taken care of, it may become long and abundant, giving the horse great beauty. The forelock is the part of the mane that grows between the ears and hangs down to cover the horse’s forehead and face.
The jugular vein, located under the jugular groove on both sides of the neck, is the site for injecting intravenous drugs and taking blood samples for clinical exams. Subcutaneous injections are given between the skin and flesh of the neck. The skin of the neck is also one of the best places to verify whether a horse is dehydrated. If the skin returns slowly to its original position after being pinched and released (known as the “skin pinch test”), this is a very distinguishable sign of dehydration (conectar estas areas resaltadas con los respectivos articulos del Chapter 10: “Health basics”).
- BARREL (or MIDDLE SECTION): This is the largest section of the horse’s body that includes the withers, back, loin, shoulders, chest, thorax, ventral edge, girth area, abdomen, inguinal region, and flanks.
The withers is located at the point where the back joins the neck. It also may be defined as the highest point where the back joins the crest. Withers is formed by the upper edges of the third, fourth, and fifth thoracic vertebrae. The highest point of the withers is where the horse’s height is measured.
The back starts at the withers and projects backward to the loin. The back is the upper line of the barrel, where the saddle should be placed, and the rider should sit. The back is supported by the withers, the other 13 thoracic vertebrae behind the withers, and some muscles. Ideally, the back behind the withers should be as straight as possible and very firm. Conversely, a significant downward curvature called “swayback appearance” or “lordosis” is not desirable because it is considered a weak back.
The shoulders, or scapulas, project down from the withers to the corners of the chest on both sides of the horse. Each scapula may be felt under the skin by touching its flat surface.
The thorax is the cage that protects many internal organs. The thoracic vertebrae (on the top of the barrel) are attached to the upper ends of the ribs on both sides of the horse. The lower ends of the 18 pairs of ribs join directly or indirectly (by means of cartilage) to the sternum, a bone at the bottom of the thorax. The ribs should be thick and rounded to provide resistance; additionally, they are arched and long to provide deepness to the barrel and room for the vital organs. In the spaces between the ribs, there are bands of intercostal muscles that allow a slight expansion of the thorax for breathing and for movement.
The chest is the frontal region of the barrel located below the neck. The upper corners of the chest, on both sides, end at the points of the shoulders. The lower edge of the chest ends at the sternum. Keeping in mind that the horse is an athlete, a wide and deep chest provides more room for the organs of the circulatory and the respiratory systems, which has many advantages during exercise.
The loin is located behind the back and supported by six lumbar vertebrae. Although it is not attached to the ribs, the loin is joined firmly to the back and to the hips by strong muscles. The horse should not be sensitive to pressure on the loin; in most cases, this discomfort is caused by an ill -fitting saddle. In more serious circumstances, it may be a sign of kidney problems.
The ventral (lower) edge of the barrel is formed by the girth area and the abdomen. Because the sternum provides a firm structure at the girth area, it is where the saddle’s cinch (or girth) should be placed. The girth area starts just behind the elbows and projects backward to the rear end of the sternum, ending in line with the abdomen.
The front of the abdomen starts at both the rear of the sternum and the lower end of the false ribs. The sides of the abdomen extend backwards to the flanks and its bottom to the inguinal region. Some horses have a big, rounded abdomen, while others have a small one. However, the size of the abdomen may vary depending on the amount and kind of food contained in the intestine; for example, a horse has a bigger abdomen when it is kept in a pasture full- time than when it is fed in a stall or corral with hay and grain on a regular schedule.
The inguinal region is located behind the rear end of the abdomen and between the thighs. The penis and testicles (in the male) and the udder (in the mare) are located in the inguinal region.
The flank (one on each side of the horse) is located a few inches in front and below the hip bone and extend downward to the abdomen, just behind the false ribs and above the inguinal region. The flank is easy to recognize where there is a change of direction in the way coat hairs grow in between the rear end of the abdomen sides and the hindquarters. Flanks have no bones in their structure.
- HIPS: The hips are located behind the loin, in front of the tail, and above the hind legs. The bone structure of the hip is formed by the “sacrum” and the pelvic girdle (ilium, ischium, and pubis). Hips have a big muscle mass around the bones, making them a good place to give intramuscular injections.
The two hip bones, or tuber coxaes, are the hardest points on each side of the hips. These bones are located behind the upper edge of each flank. The tuber ischiies, or buttock bones, are at the back end of the hips, located on both sides below the root of the tail.
The croup is the upper, narrow band on top of the hips. The bone structure of the croup is formed by the five sacral vertebrae that are fused into only one bone, called the “sacrum.” Although the croup should be slightly inclined, a croup with too great a downward incline is less beautiful and presents more risk for a mare when foaling. The perineum is the narrow band between the anus and the scrotum in the male, and between the vulva and the udder in the female.
- TAIL: The tail is located behind the sacrum and projects downward. The tail is formed by the coccygeal vertebrae, many tendons (that provide great mobility), veins, arterioles, nerves, and skin. Many long hairs (known as the “tail’s skirt”), similar to those of the mane, grow out of the lateral and the upper surfaces of the tail, which give the horse beauty and grace.
The tail serves several important functions. The horse may use it to swat flies and as a fan to comfort a friendly neighbor. It also helps the horse maintain proper balance when running and is a very effective cover that protects the anus and the vulva.
- LEGS: The horse is a quadruped, which allows it to reach high speeds when running. The two front legs, or forelegs, sustain from 55% to 60% of the body weight, and their main function is for support. The two rear legs, or hind legs, sustain the remaining 40% to 45% of the body weight. The other function of the hind legs is propulsion.
The bones, ligaments, muscles, and tendons of the legs allow the horse to walk, run, jump, carry, and pull. Each joint is embraced by ligaments to keep the bones involved together. The muscles and the tendons of the legs pull the bones above and below the joints to cause movement. Each leg ends in a single “toe” protected by the hoof, which consists of material similar to human fingernails (see Chapter 7: “Hoof trimming and shoeing”).
- Forelegs: From bottom to top, the foreleg is described as follows: The hoof covers the third phalanx (also known as “coffin bone”), the navicular bone (or distal sesamoid), and the very lower end of the second phalanx. The upper end of the third phalanx joins with the lower end of the second phalanx at the coffin joint.
The upper end of the second phalanx joins the lower end of the first phalanx at the pastern joint. The pastern is the lower end of the leg above the hoof, which includes the first phalanx, located on top, and most of the second phalanx, located at the bottom. The pastern is inclined forward in the same direction and approximately the same degree as the scapula of the horse.
(3-2b) about 3.9” wide and centered ????
The upper end of the first phalanx joins the lower end of the cannon bone, at the fetlock joint. In addition, the two proximal sesamoid bones are located at the back and the bottom of the cannon bone. The ergot is a callous, cone-shaped structure at the rear of the fetlock, made of the same material as the hooves, but slightly softer. The long coat hairs on the skin around the ergot are called “feathers”; they allow the sweat, coming down from the body, to drain. When the feathering is cut for aesthetic reasons, the sweat drains through the rear of the pastern and may irritate the skin of some horses.
The cannon bone projects straight up from the fetlock joint, and has two small splint bones attached to it on each side. The upper end of the cannon bone joins the lower articulating surface of the carpus joint or “false knee” (also known as “horse’s knee”). The carpus is a joint formed by two rows of four small bones. The upper articulating surface of the carpus joins the lower end of the forearm. The forearm projects straight up.
The chestnut is a 1 to 2-inch-long, oval-shaped, callous structure made of similar material as the ergot. The chestnut of the foreleg is located on the inside surface of the forearm, 1 ½ to 3 inches above the carpus joint.
The forearm’s bones are called the “radius” (the longest bone) and the “ulna” (a small bone that is joined to the top end of the radius, also known as the “point of elbow” or “olecranon process”). When the horse is viewed from the side, the “point of elbow” is easy to identify where the rear edge of the foreleg joins the lower edge of the barrel.
The upper end of the forearm joins the lower end of the arm at the elbow joint. The arm projects up forward and joins the shoulder. The arm’s only bone is the humerus.
- Hind legs: From bottom to top, the hind leg has the same internal structures of the foreleg: hoof, pastern, fetlock joint, and cannon bone.
The hind cannon bone projects straight up from the fetlock joint, and has two small splint bones attached to it on each side. The upper end of the hind cannon bone joins the lower articulating surface of the tarsus or hock. The hock is a joint formed by seven small bones. The chestnut of the hind leg is located on the inside surface of the tarsus at its bottom. It is usually slightly smaller than the chestnut of the foreleg.
The hock joins the lower end of the gaskin. The tibia (the longest bone) and the small fibula (a bone that is joined to the tibia on one side) are the bones that make up the gaskin. The gaskin projects up and forward to the stifle joint. The patella is a small bone at the front of the stifle joint. The thigh has only one bone, called the femur. The lower end of the femur joins the stifle joint. The thigh projects diagonally up to the hip joint.
- SKIN: It is formed by the epidermis (the most external layer) and the dermis (under the epidermis), and hypodermis (under the dermis). The skin covers the entire body and is excellent protection from outside agents. The skin has nerve endings that make up part of the sense of touch. Additionally, the skin has a blood supply (capillaries), hair follicles, glands (sebaceous and sweat glands), and muscle fibers in some areas. Even though the horse’s skin is strong, it often takes a long time to heal after being wounded or burned.
When the horse’s internal temperature gets high, the warmer blood is taken through veins that are close to the body’s skin and the sweat glands release sweat on the skin surface. Through the evaporation of sweat, the blood cools down. Therefore, a ´web´ of veins around the neck, shoulder, belly, and thighs are easy to see under the skin after several minutes of physical activity; this is a sign of good thermoregulation, which keeps the horse more comfortable during exercise.
- COAT: One of the primary functions of the coat is to provide protection from cold and hot weather. Thousands of small hairs cover the entire skin, except on the nostrils, lips, anus, genital organs, udder, inside the thighs, perineum, and underneath the tail. The colors of coat, mane, and tail are defined by genetic inheritance.
Where each hair grows, there is also a small sebaceous gland that secretes a kind of oil that protects the hairs and provides luster to the coat. The condition of the coat indicates the general condition of the horse and is a good indication that the horse lives in a favorable environment. When the coat is in optimal condition, the hairs are short, shiny, and silky.