Horse anatomy
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The anatomy of the horse comes with a large number of horse specific terms.
Contents |
[edit] External anatomy
- See also: Equine forelimb anatomy
- back: the area right behind the withers, where the saddle goes, extends to the last thoracic vertebrae
- barrel: the rounded side of the horse, which is due to the rib cage
- cannon: The area between the knee or hock and the fetlock joint, sometimes called the "shin" of the horse, though technically it is the metacarpal III.
- chestnut: a callousity on the inside of each leg
- chin groove: the part of the horse's head right behind the lower lip (the area that dips down slightly on the lower jaw). Area where the curb chain of certain bits is fastened.
- coronet: The part of the leg just above the hoof and below the pastern.
- crest: the upper portion of the neck where the mane grows.
- croup: the highest point of the horses hindquarters, made up of the highest lumbar vertebrae and extending up to the coccygeal vertebrae
- dock: the point where the tail connects to the rear of the horse.
- elbow: the front leg equivalent to the stifle. The joint of the front leg that is right at the point where the belly of the horse meets the leg. This joint extends backward when a horse jumps an obstacle.
- fetlock: Sometimes (incorrectly) called the "ankle" of the horse, though it is not the same skeletal structure as an ankle in humans. Known to anatomists as the metacarpophalangeal joint.
- flank: Where the hind legs and the barrel of the horse meet, specifically the area right behind the rib cage and in front of the stifle joint.
- forearm: the area of the front leg above the knee and below the elbow. Consists of the radius, ulna, and all the tissue around these bones.
- forelock: the continuation of the mane, which hangs from between the ears down onto the forehead of the horse
- frog: the highly elastic wedge-shaped mass on the underside of the hoof, which normally makes contact with the ground every stride, supports both the locomotion and circulation of the horse.
- gaskin: also known (incorrectly) as the "second thigh," the large muscle on the hind leg, just above the hock, below the stifle.
- girth: the area right behind the elbow of the horse, where the girth of the saddle would go
- hindquarters: the large, muscular area of the hind legs, above the stifle and behind the barrel of the horse
- hock: The tarsus of the horse (hindlimb equivalent to the human heel), the main joint on the hind leg.
- hoof: The foot of the horse. The hoof wall is the tough outside covering of the hoof that comes into contact with the ground.
- jugular groove: the line of indentation on the lower portion of the neck, can be seen from either side
- knee: the carpus of the horse (equivalent to the human wrist), the large joint in the front legs, above the cannon bone
- loin: the area right behind the saddle, going from the last rib of the horse to the croup.
- mane: long and relatively coarse hair growing from the dorsal ridge of the neck, lying on either the left or right side of the neck (See illustration.)
- muzzle: the chin, mouth, and nostrils make up the muzzle on the horse's face.
- pastern: The connection between the coronet and the fetlock. Made up of the middle and proximal phalanx.
- poll: the portion of the horse's neck right behind the ears.
- splints: bones found on each of the legs, on either side of the cannon bone (8 total). Thought to be vestigages, serve no known purpose to the horse.
- shoulder: made up of the scapula. Runs from the withers to the point of shoulder (the joint at the front of the chest). The angle of the shoulder has a great affect on the horse's movement and jumping ability, and is an important aspect of equine conformation.
- stifle: The patella, corresponds to the kneecap of a human.
- tail: consists of both the living part of the tail (which consists of the coccygeal vertebrae, muscules, and ligaments), as well as the long hairs which grow from the living part
- throatlatch: The point at which the windpipe meets the head at the underside of the jaw.
- withers: the highest point of the thoracic vertebrae, the point just above the tops of the shoulder blades. Seen best with horse standing square and head slightly lowered. The height of the horse is measured at the withers in "hands."
[edit] Teeth
A horse's teeth include incisors, premolars, molars, and sometimes canine teeth. A horse's which grow throughout the animal's lifetime. Horses, depending on age and gender, have between 24 and 42 teeth.
[edit] Feet/Hooves
The hoof of the horse encases the second and third phalanx of the lower limbs, analogous to the fingertip or toe tip of a human. In essence, a horse travels on its "tiptoes." The hoof wall is a much larger, thicker and stronger version of the human fingernail or toenail, made up of similar materials.
[edit] Skeletal system
The skeletal system has three major functions in the body. It protects vital organs, provides framework, and supports soft parts of the body. Horses have 205 bones. Both pelvic and and thoracic limbs contain the same number of bones, 20 bones per limb. The vertebral column has 54 bones and the skull has 34 bones. The sternum consists of only one bone and there are 18 pairs of ribs.
Bones serve three major functions in the skeletal system; they act as levers, they store minerals, and they are the site of red blood cell formation. Bones can be classified into four categories
- Long Bones: aid in locomotion, store minerals, and act as levers. They are found mainly in the limbs.
- Short Bones: Absorb concussion. Found in joints such as the knee, hock, and fetlock.
- Flat Bones: Enclose body cavities containing organs. The ribs are examples of flat bones.
- Irregular Bones: Protect the central nervous system. The vertebral column consists of irregular bones.
Ligaments and tendons hold the skeletal system together. Ligaments hold bones to bones and tendons hold bones to muscles. Synovial membranes are found in joint capsules. Synovial membranes contain synovial fluid, which lubricates joints. Bones are covered by a tough membrane called periosteum, which covers the entire bone excluding areas of articulation.
The skull contains four cavities: the cranial cavity, the orbital cavity, oral, and the nasal cavity. The cranial cavity encloses and protects the brain and it supports several sense organs. The orbital cavitity surrounds and protects the eye. The oral cavity is a passage way into the respiratory and digestive systems. The nasal cavity leads into the respiratory system. The nasal cavity contains turbinate bones that protect the mucous membrane that lines the cavity from warm inspired air. The skull consists of seven major bones
- Incisive bone (premaxillary): part of the upper jaw; where the incisors attach
- Nasal bone: covers the nasal cavity
- Maxillary bone: the upper portion of the jaw
- Mandible: lower portion of the jaw; largest bone in the skull
- Orbit: bone located around the eye
- Frontal bone: creates the forehead of the horse
- Temporal fossa: found behind the ears near the vertebral column
[edit] Digestive system
- See also: Equine nutrition
Horses and other Equids evolved as grazing animals, adapted to eating small amounts of the same kind of food all day long. In the wild, the horse adapted to eating prairie grasses in semi-arid regions and traveling significant distances each day in order to obtain adequate nutrition.[1] Therefore, the digestive system of a horse is about 100 feet long, and most of this is intestines.
[edit] The mouth
Digestion begins in the mouth, which is also called the "oral cavity." It is made up of the teeth, the hard palate, the soft palate, the tongue and related muscles, the cheeks and the lips. Horses also have four pairs of salavary glands. Horses select pieces of forage and pick up finer foods, such as grain, with their sensitive, prehensile, lips.The front teeth of the horse, called incisors, clip forage, and food is then pushed back in the mouth by the tongue, and ground up for swallowing by the premolars and molars. [2]
[edit] The esophagus
The esophagus is about 5 feet in length, and carries food to the stomach. The esophagus enters the stomach at an acute angle, creating a one-way valve, with a powerful spincter mechanism at the gastroesophageal junction, which is why horses cannot vomit.[2] The esophagus is also the area of the digestive tract where horses may suffer from choke. (see also: choke (horse))
[edit] The stomach
Horses have a relatively small stomach for their size, and this limits the amount of feed a horse can take in at one time. The average sized horse (800 to 1200 lbs) has a stomach with a capacity of only four gallons, and works best when it contains about two gallons. Because the stomach empties when 2/3 full, whether stomach enzymes have completed their processing of the food or not, and doing so prevents full digestion and proper utilization of feed, continuous foraging or several small feedings per day are preferable to one or two large ones.[2] The horse stomach consists of a non-glandular blind sac (saccus cecus), divided by a distinct border, the margo plicata, from the glandular stomach.[citation needed]
In the stomach, assorted acids and the enzyme pepsin break down food. Pepsin allows for the further breakdown of proteins into amino acid chains.[2] Other enzymes include resin and lipase. Additionally, the stomach absorbs some water, as well as ions and lipid soluble compounds. The the end product is food broken down into chyme.[citation needed] It then leaves the stomach through the pyloric valve, which controls the flow of food out of stomach.[citation needed]
[edit] The small intestine
The horse’s small intestine is 50 to 70 feet long and holds 10 to 12 gallons. This is the major digestive organ, and where most nutrients are absorbed.[3] It has three parts, the duedenum, jejunum and ileum. Bile from the liver acts here, combined with enzymes from the pancreas and small intestine itself. Horses do not have a gall bladder, so bile flows constantly. [2] Most food is digested and absorbed into the bloodstream from the small intestine, including proteins, simple carbohydrates, and fats. Any remaining liquids and roughage move into the large intestine.
[edit] The cecum and large intestine
The cecum is the first section of the large intestine. It is also known as the "water gut" or "hind gut." It is a cul-de-sac pouch,[3] about 4 feet long that holds 7 to 8 gallons. It contains bacteria that digest cellulose plant fiber through fermentation.[4] These bacteria feed upon digestive chyme, and also produce certain fat-soluble vitamins which are absorbed by the horse.[2] The reason horses must have their diets changed slowly is so the bacteria in the cecum are able to modify and adapt to the different chemical structure of new feedstuffs.[3] Too abrupt a change in diet can cause colic, as the new food is not properly digested.
The large colon, small colon, and rectum make up the remainder of the large intestine. The large colon is 10-12 feet long and holds up to 20 gallons of semi-liquid matter. It is made up of the right lower (ventral) colon, the left lower (ventral) colon, the left upper (dorsal) colon, the right upper (dorsal) colon, and the transverse colon.[2] Its main purpose it to absorb carbohydrates which were broken down from cellulose in the cecum. Due to its many twists and turns, it is a common place for a type of horse colic called an impaction.[4][3]
The small colon leads is 10-12 feet in length and holds only 5 gallons of material. It is the area where the majority of water in the horse's diet is absorbed, and is also the place where fecal balls are formed. The rectum is about one foot long, and acts as a holding chamber for waste matter, which is then expelled from the body via the anus.[2]
[edit] References
- ^ Budiansky, Stephen. The Nature of Horses. Free Press, 1997. ISBN 0-684-82768-9
- ^ a b c d e f g h Giffen, James M. and Tom Gore. ‘’Horse Owner’s Veterinary Handbook., 2nd ed. New York:Howell Book House, 1989, 1998. ISBN 0876056060
- ^ a b c d "Horse Nutrition - The Horse's Digestive System." Bulletin 762-00, Ohio State University. Web site accessed February 9, 2007.
- ^ a b Williams, Carey A.,Ph.D., Extension Specialist. "The Basics of Equine Nutrition" from FS #038, Equine Science Center, Rutgers University, Revised: April 2004. Web site accessed February 9, 2007
