Anatomy of the Horse
INSTRUCTOR:
UNIT: Knowledge of the Nutritional Requirements for Horses
LESSON: Anatomy of the Horse
IMS REFERENCE: IMS #8893-A
TOPIC NOTES
ANATOMY OF THE HORSE
A dressage* horse named Cal from Illinois
developed a disease known as high
ringbone, which is an excessive bony
growth around the pastern bone above the
hoof. To determine the nature of the
problem, veterinarians at the University of
Illinois Equine Clinic used a complicated
procedure of X-rays combined with nuclear
scintigraphy, where radioactive materials are
injected in the blood to detect “hot spots” in
the horse’s anatomy. Because the ringbone
made Cal lame even at a walk, surgery was
the only alternative. Cal’s veterinarians
removed the excess bony material and
fastened a metal plate into the bone with
metal screws. Then, they placed a fiberglass
cast on Cal’s leg, from just below the knee
to above the hoof. Cal recuperated from the
surgery after several months, despite trying
to chew the top of the cast and attempting to
remove it by pawing.
A happy ending does not always occur for horses with leg injuries. Before the advent of
fiberglass casts and development of screws and plates strong enough to withstand the pressure
placed on the legs, many horses with broken legs were humanely destroyed. This example
illustrates how crucial the one part of the horse’s anatomy, the skeletal system, is to the health of
the horse.
My name is Cal, and I’m that horse that had ringbone. Isn’t modern technology wonderful? I can
certainly vouch for that. Thank goodness I’m walking and running around with no pain or
limping; it was really a bummer being stove up with ringbone. I’ll be taking you on a tour of the
various parts of the horse’s anatomy, being an expert in that area myself. You’ll need to know the
parts of the horse’s body and its various systems to select a good mount and realize the effects of
illness and injuries on our species and how treatments for injuries and illnesses improve our
health. You’ll have to learn a lot of fancy but necessary words used in anatomy, so I’ll apologize
for that ahead of time. You’ll also need to know these terms to describe a problem to the
veterinarian, or even to discuss horses with your horse-loving friends or horse industry
professionals. Let’s start the tour!
* Underlined words are defined in the Glossary of Terms.
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Anatomy of the Horse
My body consists of a framework called the skeleton that is covered by muscles and enclosed in
the skin. Within the skeletal framework lie the different organs such as the heart, lungs, liver,
digestive system, nervous system, and reproductive organs. You can locate my injured, ailing,
and diseased organs, bones, and muscles if you’re familiar with my anatomy.
PARTS OF THE HORSE
One simple way for you to learn the terms is to study Figure 1. Then you can look at a live horse,
perhaps with a partner, and point out and describe the parts. You and your partner can unofficially
quiz each other by having each of you point to and name each body part. Be careful and don’t
poke and prod me, because I am touchy in certain places.
SKELETON OF THE HORSE
Did you know my skeleton consists of approximately 210 bones? The skeleton provides support
for the muscles and protection for the organs. It has mobility of its parts to allow me to move at
different speeds, lie down, and graze.
I have approximately 54 bones in my vertebral column. This number varies because different
horses have different numbers of coccygeal (tail) vertebrae. Most of my species have 18 tail
vertebrae. In addition, my vertebral column contains 7 neck (cervical), 18 back (dorsal), 6 loin
(lumbar), and 5 croup (sacral) vertebrae. For those of us with correct conformation, the lower line
of the backbone, or dorsal vertebrae, arches slightly upward. If a horse’s backbone arches too far
upward or sags downward, the horse’s conformation is weak. Most humans don’t like that.
Did you realize that a close relationship exists between the length of each vertebrae and the
composite length of other skeletal parts. Thus, a horse with long vertebrae has a long neck, back,
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Anatomy of the Horse
loin, croup, and tailbone. Most human horse folks desire length in a horse. For example, a long
neck on a riding horse makes the horse look balanced and graceful. However, some extremely
lengthy horses are just too long to be strong. For example, a horse with a very long back and loin
is often weak in the back.
Below the vertebrae are the ribs. Most of us have 18 pairs of ribs, but like the vertebrae, this
number can vary. A horse with nineteen ribs on one side or the other is not rare. I bet you didn’t
know that horses had such variety! Long, well-sprung ribs are desirable in a horse. This provides
a large space for the vital internal organs. Those of us with large, wide chests and middles often
eat better and withstand hard work more efficiently, as we have more room for lung development.
The breastbone (sternum) of the horse consists of seven fused segments. The sternum is flat from
side to side and is canoe-shaped — it’s difficult to see this canoe shape from an illustration, but
the “canoe” is in the middle of the chest and extends backwards to between our legs toward the
bottom of the belly. The ribs are attached to the sides of the sternum by cartilage.
A skull encloses my brain and some important sense organs. The major functions of the skull are
to protect the brain and provide cavities for the eyes and the respiratory system. My skull has
some special adaptations to meet particular requirements. The long face of my skull provides
space for my teeth and their long roots. The openings that house my eyes are well above ground
level when I am grazing, so that I can look around more easily for impending danger.
The thoracic limbs include all of the bones in the front legs. My front legs and feet are very
important because they carry about 60% of my weight and are under a lot of stress. The alignment
of the leg bones determines the way that I move. Humans require us horses to have correctness of
the bone structure of the front legs because it affects our usefulness and value. Crooked bones
turned inward or outward are not allowed by your perfectionist species — you have all sorts of
names for such deficiencies: cow-hocked (imagine that, comparing us to a cow!) and pigeon-toed
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Anatomy of the Horse
(now that really gets my goat; you’re comparing apples and carrots there, horses and birds just
cannot be compared!).
Although I don’t know why anyone would want to do so, some people compare a horse’s front
leg to a human’s arm. They see both similarities and differences. The same bones are present, but
the orientation of these bones is rather different. Refer to Figure 2 for more information. For
example, the radius and ulna are fused together in the horse, while they are separate in a human.
The knee joint in the horse is the counterpart of the wrist in a person. The cannon bone
(metacarpus) and bones of the foot in the horse would be the bones of a person’s hand. The horse
basically walks on the tip of the toe, of course it’s a very big tip at that, not like the small human
toe. The toenail in a human compares with the hoof in a horse, but our toenails are much thicker.
Large muscles cover the bones in our upper front legs. These bones are called the scapula, or
shoulder blade in humans, and the humerus, or upper arm bone. These bones are moveable, but
are not as free moving as the same bones in humans. The scapula does not attach to the backbone
of the horse the same way as it does in a human. Muscles attach the scapula to the backbone in
the horse, contrary to the collarbone and joint attachment in a human.
My hind legs (pelvic limbs) are my main means of propelling myself forward. My stifle joint
corresponds to your knee joint. Did you know that my stifle joint has a locking mechanism that
enables me to sleep while standing? Sometimes this mechanism sticks, and a horse cannot bend
the joint. The common term for this condition is “stifled.” In such a case, a veterinarian must
operate on the horse and cut the ligament that causes the joint to lock. After the surgery, the horse
can no longer sleep while standing, but fortunately it is able to otherwise function normally.
Your ankle joint is the counterpart to my hock joint. The hock is the most important single joint
of the horse. Horses have more serious unsoundness in the hocks than in any other part of the
body. The problem with hocks is that they are the most complex joints in the body. That’s why so
many things can go wrong with them. The hocks must be structurally sound for a horse to move
and perform well.
MUSCLES
The next stop on the tour are the muscles, which may be of special interest to those of you who
lift weights. The muscles that enable us to move consist of muscle masses attached to bone at one
end and tendons at the other. Muscles move bones by contracting and relaxing. As a muscle
contracts, it pulls a bone. The opposite muscle or muscles relax and allow the bone to move.
Refer to Figure 3 for the muscles of the horse.
Now to get into the physics of it, muscles that move the skeleton use simple machines, such as
levers, to increase the efficiency of their work. I’m proud to say that our muscular system is very
complex and works amazingly well to produce a large variety of movements. I wonder if you
realize that horses develop their muscles too by lifting weights, such as carrying people and packs
and pulling carts. You would have to say our leverage system works pretty darned good, because
people rate the power of engines in “horsepower.”
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Anatomy of the Horse
Neck muscles should be long, smooth, and flat. Such muscles increase the ease and freedom of
movement of my forelegs. Lack of muscle length reduces the movement of my forelegs and
makes me rough to ride. If I have too much heavy muscling on the underside of my neck, that can
cause problems maintaining my proper head set and carriage. These are things humans deem very
important in their pursuit of various riding styles; I can certainly tell that those things are
extremely important in dressage.
Additionally, heavy muscling shifts the horse’s center of gravity forward, leading to lameness.
The forearm muscles should be long and lean and attach to the bone close to the knee. With this
type of muscling, we produce long strides, especially when the cannon bone is relatively short.
Long muscles make it easier for us to lift our forelegs, thus contributing to ease and freedom of
movement.
We have muscles in our back and loin that help support the weight of a rider. The vertebral
column is the only support for the loin, thus a lack of muscling usually leads to a sagging back
(swayback). The degree of muscling in the hindquarters is associated with the breed of horse and
its purpose. Events that emphasize power require large, bulging muscles, while events that require
speed need long, tapering muscles. Quarterhorses usually exhibit heavy muscling compared to the
lean muscling of racing thoroughbreds. Dressage horses, such as myself, are usually intermediate
in muscling between quarterhorses and thoroughbreds, although you will see both of those breeds
in my sport.
Did you know that muscles are attached to bones by tendons? As the muscle contracts, the tendon
resists stretching and pulls on the attached bone. Tendons are encased in thin, fibrous sheets
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(tendon sheaths) that secrete an oily substance. This tendon oil, or synovia, lubricates the tendon
and so that the tendon can move freely, somewhat similar to motor oil lubricating the moving
parts of an engine. The lower legs contain
several long tendons extending from the muscles in the forearms to the bones in the feet. You can
feel the tendons running down the horse’s leg behind the cannon bone. These tendons are
responsible for moving the horse’s feet, and they must be strong and tight. Weak tendons lead to
lameness and unsoundness.
ORGANS OF THE THORACIC CAVITY
Our next touring station is the thoracic cavity. The thoracic cavity includes the area between the
neck and the abdomen in the horse. The ribs form the sides of the cavity. Our thoracic cavity
contains vital organs of the circulatory and respiratory systems. Our heart lies towards the bottom
of the thoracic cavity (just inside the sternum). The heart lies to the left of center, so you can feel
the pulse just behind the horse’s left elbow. As in other mammals, the horse’s heart consists of
four chambers. The heart acts as a pump, moving blood throughout the horse’s body. Did you
realize that racehorses have hearts that are larger than the average horse’s heart? The muscles of a
racehorse require more oxygen than do the muscles of an average horse, and the heart enlarges to
pump more blood to supply that oxygen.
Our lungs lie to the sides of and behind the heart, filling most of the thoracic cavity. Exchange of
oxygen and carbon dioxide between the blood and the air takes place in the lungs. The walls of
the thoracic cavity expand and contract, forcing air into and out of the lungs, otherwise known as
breathing. The lungs then exchange oxygen from the air for carbon dioxide in the blood. Next, the
oxygen travels in the blood to the muscles and other tissues. Living tissues need oxygen for
energy production. The lungs must be large and functional for a horse, especially a working
horse, to be able to perform adequately. Horses have very efficient oxygen carrying circulatory
systems and therefore are able to exercise long and hard.
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exchange oxygen from the air for carbon dioxide in the blood. Next, the oxygen travels in the blood to the
muscles and other tissues. Living tissues need oxygen for energy production. The lungs must be large and
functional for a horse, especially a working horse, to be able to perform adequately. Horses have very
Anatomy of the Horse
efficient oxygen carrying circulatory systems and therefore are able to exercise long and hard.
Figure 4. Organs of the thoracic cavity (simplified).
ORGANS OF THE ABDOMINAL CAVITY
-6Next we’ll go to the abdominal cavity, which extends from just behind the thoracic cavity to the
pelvic region. The diaphragm separates the abdomen from the thorax. We’ve got some very
important organs in this area. The abdominal cavity contains the liver, spleen, kidneys, and
organs of the digestive system. The liver lies just behind the diaphragm. The liver is a large
organ, extending all the way across the abdominal cavity. The liver is a fascinating organ and has
many functions, including metabolism of several nutrients, detoxification of many drugs and
poisons, and storage of some nutrients. The spleen and stomach lie behind the liver and in front of
the small and large intestines. These organs are part of the gastrointestinal (G.I.) tract and
function in the digestion and utilization of food. Digestive disorders, something to which horses
are prone, occur most often in the abdomen. You can sometimes tell if a horse has a G.I. tract
problem by listening to noises in the abdomen. Unusual noises or the lack of normal noises can
indicate that something is wrong. Normally, a fair amount of gurgling goes on in our guts.
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Figure 5. Organs of the abdominal cavity (simplified.
Our kidneys are in the loin area, one on each side of the backbone. They lie under the last ribs and
first lumbar vertebrae. Kidneys remove wastes from the body and conserve fluids and important
components of blood. When we have sensitive and sore backs, it’s sometimes caused by kidney
disorders.
ORGANS OF THE PELVIC CAVITY
Next on the tour is the pelvic cavity; it is continuous with the abdominal cavity. Several organs lie
within both the abdominal and pelvic cavities. For instance, the rectum, the terminal portion of
the intestine, continues from the abdominal cavity into the pelvic cavity. The urinary bladder is
another example. When empty, the urinary bladder lies within the pelvic cavity. However, the
bladder extends into the abdominal cavity when it is full.
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Next on the tour is the pelvic cavity; it is continuous with the abdominal cavity. Several organs lie within
both the abdominal and pelvic cavities. For instance, the rectum, the terminal portion of the intestine,
continues from the abdominal cavity into the pelvic cavity. The urinary bladder is another example. When
Anatomy
of the
Horse
empty, the urinary
bladder
lies
within the pelvic cavity. However, the bladder extends into the abdominal
cavity when it is full.
Figure 6. Reproductive tract of a mare (simplified).
Figure 7. Reproductive tract of a stallion (simplified).
Our pelvic cavity also contains the male -or8 female
reproductive organs. The male reproductive
organs lie toward the back and at the base of the pelvic cavity. The female reproductive organs
extend from the back of the cavity to near the abdominal cavity in the horse. Veterinarians often
palpate the reproductive organs to detect abnormalities. The veterinarian can feel the cervix,
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Anatomy of the Horse
uterus, ovaries, and even the left kidney in the female. In the male, he or she can feel the left
kidney and part of the bladder to check for urinary tract abnormalities. The veterinarian can also
feel some glands of the reproductive system to check for problems in the male horse.
SELECTED WEB SITES FOR INFORMATION ON HORSE ANATOMY
http://members.aol.com/JaniceBr/anatomy.htm http://members.tripod.com/cavanaughc/id231.htm
http://www.angelfire.com/tx2/horsecorral/horseanatomy.html
http://www.circlekhorsepavilion.com/circlek/horseparts.html
http://www.circlekhorsepavilion.com/circlek/anatomyquizans.html http://www.eclectichorseman.com/interactive/horse_anatomy.php http://www.spequine.com/anatomy.htm
http://www.theponycrazyclub.com/anatomy.html http://www.timberoaksfarm.com/quiz.htm
http://www.upperegypt.com/vet_services/horse_anatomy/horse_anatomy.htm
ACKNOWLEDGEMENTS
Sabrina Tuttle, Graduate Technician, Department of Agricultural Education, Texas A&M
University, researched and developed this topic.
Larry Ermis, Curriculum Specialist, Instructional Materials Service, Texas A&M University,
reviewed and edited this topic.
Vickie Marriott, Office Software Associate, Instructional Materials Service, Texas A&M
University, edited and prepared the layout and design for this topic.
Christine Stetter, Artist, Instructional Materials Service, Texas A&M University, prepared the
illustrations for this topic.
REFERENCES
Bradley, M. Horses-A Practical and Scientific Approach. New York, NY: McGraw-Hill,
1981.
Edwards, E. H. Encyclopedia of the Horse. New York, NY: Crescent Books, 1994.
Ensminger, M. E. Horses and Horsemanship. Danville, IL: Interstate Printers and
Publishers, 1999.
Evans, J. W. Horses: A Guide to Selection, Care, and Improvement. New York, NY: W.
H. Freeman and Co., 2001.
McCurnin, D. M. Clinical Textbook for Veterinary Technicians. Philadelphia: W.B.
Saunders Company, 1994.
Shively, M. J. Veterinary Anatomy: Basic, Comparative, and Clinical. College Station,
TX: Texas A&M University Press, 1985.
Williams, A. (2002). The Story of Cal. IDCTA Newsletter. [On-line]. Available:
www.idcta.org/newsletter/ February/Cal.htm [2002, October 11]
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Anatomy of the Horse
GLOSSARY OF TERMS
Abdomen – The part of the body between the thorax and the pelvis (the belly region).
Cartilage – A translucent elastic tissue that composes most of the skeleton of embryos and very
young vertebrates and which is replaced by bone as the animal matures.
Detoxification – The act of removing poison or the effects of a poison.
Diaphragm – A body partition of muscle and connective tissue that separates the thoracic cavity
from the abdominal cavity.
Dressage – The guiding of a horse through a series of complex maneuvers by slight movements
of the rider’s hands, legs, and weight.
Metabolism – The physical and chemical processes in an organism by which living matter is
produced, maintained, and destroyed, and by means of which energy is made available.
Nutrients – Substances that provide nourishment for the body.
Palpate – To examine by touch.
Scintigraphy – A diagnostic technique in which a two-dimensional picture of a bodily radiation
source is obtained by the use of radioisotopes.
Thoracic – Of or pertaining to the thorax (the area between the neck and the abdomen).
Vertebrae – Any of the bones or segments in the spinal column.
Vertebral column – The backbone.
TOPIC ACTIVITIES
TRUE/FALSE: Circle the “True” if the statement is true or “False” if it is false.
1. The hock is the most complex single joint in the horse.
a. True
b. False
2. Muscles of the horse move the bones by contracting and relaxing.
a. True
b. False
3. Muscles in the horse’s neck should be large and bulky for strength.
a. True
b. False
4. Muscles in a horse’s back and loin support the rider.
a. True
b. False
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5. The horse’s thoracic cavity contains circulatory and reproductive systems’ organs.
a. True
b. False
6. The diaphragm separates the horse’s thoracic cavity from the pelvic cavity.
a. True
b. False
7. The kidneys lie in the horse’s abdominal cavity.
a. True
b. False
8. Unusual noises in the abdominal cavity indicate that a horse has a G.I. tract problem.
a. True
b. False
9. Sensitive backs in horses may be caused by kidney disorders.
a. True
b. False
10. The rectum lies within the horse’s abdominal and pelvic cavities.
a. True
b. False
11. The urinary bladder lies within the horse’s abdominal and pelvic cavities when empty.
a. True
b. False
12. Label the parts of the horse using the following illustration.
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SHORT ANSWER/LISTING: Answer the following question or statements in the space
provided or on additional paper.
13. List three organs that a veterinarian can feel when palpating a female horse.
14. List three organs that a veterinarian can feel when palpating a male horse.
15. Indicate the equine counterpart to the human bone or joint by inserting the names of the
bones.
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ADVANCED ACTIVITIES
1. Research and report on the uses of medical technologies (such as scintigraphy) in equine
science.
2. Using a gentle horse, identify and discuss the parts of the horse for the other students in
the class.
3. Secure bones of horses for identification.
4. Develop a working model that illustrates the actions of horse muscles.
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