In today's world of specialized equine breeding and showing, few anatomical features generate as much interest and controversy as the shape of the horse's head.
The head is obviously important. It supports and protects not only the horse's brain, but the organs of sight, smell, balance and hearing. Packed into it with incredible efficiency are the tongue, the powerful muscles required for chewing and a highly specialized set of teeth. On the surface of the head, much smaller muscles move eyelids, brows, ears and nostrils, mediating an array of expressions important to life in the herd.
As if all of that weren't enough, the head also accommodates the crucial functions of breathing and swallowing. The sinuses and a complex system of lymph nodes are the first lines of defense against dust and infective agents. The horse's sensitive yet muscular lips help him explore his environment and gather food. A rich circulatory supply nourishes all parts of the head and a ramifying network channels drain metabolic wastes.
With all this complexity, it isn't surprising that many people have questions concerning head conformation and function. The shape of a horse's head is the direct product of the of its skull. But because the of the horse's skull are vastly from ours, the actual meaning of its shape and movements can be difficult to appreciate.
Years ago, a friend and I were feeding our horses. The stable was a converted cow barn where we fed by spreading hay and grain in long troughs. The central aisle was raised several feet above where the horses stood, so that as they steadily munched their dinner, we observed them from a level slightly above their heads.
My friend pointed to the hollow place just behind her horse's eye and said, "It's nice to see the horses so contented. Look! You can see my gelding's heartbeat." "Uh," I replied, "I hate to tell you this, but that isn't his heartbeat. The appearance of pulsating or throbbing is because of the motion of his jaws as he chews. What you're seeing is the 'pumping,' the on-and-off contraction, of the temporalis muscle, one of the muscles that closes the jaws."
I'm happy to say that the denouement of this story is a good one--my friend eventually signed up for a university-sponsored course in animal anatomy--but she was so convinced that you could see the horse's heartbeat in the hollow behind the eye that she sure didn't want to believe me at the time.
THE POTENTIAL PITFALLS OF THE "EXTREME" HEAD
Over many years of teaching, I have, of course, met lots of people who did not want to believe me. And the basis for their disbelief has typically been just the same as that of my friend: confusion about the architecture and design of the horse's skull, and what the head in the living animal must be able to do to ensure that the horse has a healthy, productive life. It is an error, and I believe also a cruelty, to selectively breed horses to produce any type of "extreme" head.
A recent scientific study has demonstrated that the range of skull shapes found in different breeds of domestic dog exceeds not only that of its ancestor the wolf and its close relatives the fox, jackal, fennec, dhole and African hunting dog, but also that of the entire Order Carnivora, which includes everything from walruses at one extreme to weasels at the other. This huge range of artificially produced variability came about because the dog has been under domestication far longer than has the horse--probably at least 10 times longer--so that over the last 50,000 years, humankind has had the opportunity to perpetuate a wide range of dog head shapes.
This begs the question of how many kinds of dog were actually common in ancient times. In my capacity as the "bone lady" for the Vindolanda World Heritage archaeological site--a Roman fort and village complex in northern England (see "Vindolanda," EGUUS 341)--I have recently been pursuing research on this very question. Numerous well-preserved dog skulls from this dig date back 1,600 to 2,000 years and, fascinatingly, even at this early period there are distinctly recognizable types.
My reason for mentioning this in the context of an article on horse conformation is to point out that, among a dozen different dog types known from Roman times, all but one were viable working Ancient dogs had serious work to do: hunting deer, badgers, boar, wolves, lions and other dangerous game; and herding, tracking and guarding. None of these dogs is pugged, has a bulging forehead, or a tiny muzzle; none have twisted skulls, impacted teeth or nonfunctional tear ducts. None would have had the slightest trouble running, breathing, digging, biting, gripping of chewing. Although injuries such as broken ribs, stomped-on paws, broken legs, severe bites and concussions from being clubbed over the head are common among these skeletons, inheritable skeletal problems are an extreme rarity. Even "pariah" dogs--the mutts of their day--had sound limbs, backs free from arthritis and clean, straight teeth.
The Romans did, however, also breed and keep toy dogs. Some of these were as small as the tiniest toys seen today and they were equally extreme in the shape of the skull. Their skeletons show the whole array of problems that typically come with breeding solely for "cuteness": crowded, impacted and nonerupting teeth; weak, fragile jaws; bulging eye sockets; nonfunctional tear ducts; scoliotic spines; deformed limbs; severe arthritis and dysplasias of the hip and shoulder. Archaeologists agree that these dogs were "status items," kept in the home as pets, protected from danger and fed the only diet they could handle--vittles that had been minced or mashed until soft.
Such dogs cannot be considered working animals, but that is not to say that they had no function: They were called "comforters" because it was believed that they could help ward off disease or help in curing it--and much modern research confirms dogs' value in health and healing (though not for the reasons the Romans thought). In the Middle Ages, it became fashionable for ladies of means to hold tiny dogs close to their bosom, not merely for comfort, but because the animal also tended to act as a "flea magnet."
Admittedly, horses are not useful for drawing off fleas, but there is no question that today some are bred to fulfill the role of comforter. The modern term for this is "pasture ornament'--a pretty horse who is not a good weight carrier and is not very strong or very sound. In more than one breed, it has happened that the national champion in halter competition was exactly that.
It is not my business to dictate to any horse club or breed what they should value, but it is, I think, incumbent upon me to advise and warn consumers that an "extreme" head in a horse is no healthier, no more functional, and ultimately no more valuable than one on a toy dog. In horses as in dogs, the more extreme the head, the higher the chances of problems with tooth eruption, breathing and tear ducts.
As inbreeding intensifies, genetic diseases and congenital malformations of all types multiply, and problems with development, cognition, hypersensitivity and behavior can also make the horse difficult to work with. Extreme refinement may make the horse's spine too long or too weak to bear any load, and past a certain point, refinement of the limbs predicts unsoundness (see "A Sense of Proportion," EQUUS 388).
Magnificent examples of quality heads
Left: This Mustang stallion of the Pryor Mountain herd in Wyoming has a bite wound on his nose, but that does not detract one bit from the beauty of his head. Note the breadth between the orbits, clean attachment to the neck, large distensible nostrils, firm lips, alert expression, and lively, intelligent eye.
Below: This skull is from a horse who died 1,900 years ago. He probably belonged to one of the commandants of the Roman fort at Vindolanda. Despite cracks and breakage caused by its long burial in the ground, this skull has the shape, and crispness that are the marks of quality. A quality head so reflects the underlying bone structure that it looks almost as if it had been "carved of wax."
QUALITY IN HEADS: MORE THAN SKIN-DEEP
The bottom line is that unless the only plan you have for your horse is to admire him, pet him and nurse him, avoid extremes. Instead look for quality in a head, by which I mean look for one that is beautifully shaped. Although "extreme" does not equate with "quality," it's important to note that "functional" may not either; a head can be functional without having much quality. Quality heads must first be functional, but must also show:
* breadth across the bony orbits, so that when viewed from the front it presents a long diamond shape
* orbits placed fairly low in the head, so that the eyes do not appear high and the face and muzzle do not appear excessively long
* eyes of normal size and clarity, having an alert, intelligent and calm expression
* symmetry, so that left and right halves of the head appear equal and aligned
* large, distensible nostrils
* neat ears, carried alertly
* firm lips
* wide ganache, the space between the left and right branches of the jaw
* a chiseled appearance to the bony orbits, cheekbones, nasal bone, facial bones, forehead and bars of the jaw--giving an appearance almost as if the head were carved of wax.
Note that "bulging forehead" does not appear on this list. Nor do a dished face, tiny muzzle, short muzzle, small head, ears whose tips curve inward, small ears or eyes that appear large and bulging.
Breed isn't specified in the above list, either. Quite a few folks in the horse world today think that the "dished" type of head most desired by American Arabian breeders is the only "good" kind of head, but quality heads come in all shapes. Some have a convex facial profile, while others have straight profiles or profiles that undulate.
A horse of any breed may have a quality head. In the end, there is only one really appropriate place for an Arabian head and that is on the end of the neck of an Arabian horse. The near-total loss of the head shapes that used to distinguish the Morgan, Appaloosa, Tennessee Walker, American Saddlebred and Quarter Horse--all of which have in recent years gone over en masse to the Arabian head shape---is, in my view, really sad and a reflection of lack of knowledge about and pride in the unique history of these American breeds.
DECONSTRUCTING THE EQUINE HEAD
Modeling the horse's skull helps to simplify its innate complexity and to teach us how its components fit together to create the external shape we see. The most important and yet the least visible of the skull's parts is its "main support rod"--anatomically, the fused-together basioccipital, sphenoid and vomer bones that run straight through the center of the skull. In the development of the fetus, these bones form early to create the floor of the braincase and to support the snout. In the living animal, the main support rod is not visible because it lies between the skull above and the jaws and throat below.
The shape of the support rod is crucial because it dictates the angular relationship of the face, muzzle and jaws to the braincase. The rod is always bent downward to some degree, but it is bent more in horses with arched skull structure and less in those that have dished structure. The diagram of the horse's skull on page 51 shows the amount that the main support rod is bent downward in horses, such as most Thoroughbreds, that present "straight" skull structure--about 9 degrees.
The main support rod in the skull of a mustang or Lipizzan with convex skull shape would bend down about 13 degrees, while that of a Welsh Pony or Arabian with concave skull shape would bend down only 5 to 8 degrees. In terms of numbers, these differences may seem small, but they provide the foundation for spatial relationships among all the other parts.
Once the angle between snout and braincase is set, the orbits can be viewed as "goggles" that attach to the forward sides of the braincase. The orbits can be set closer together or farther apart, higher or lower. The frontal sinuses are placed between and below the orbits, bridging over the junction between the "box" that represents the snout and the "ball" that represents the braincase. The frontal sinuses can be nearly flat or they may be "inflated." The external shape of a correctly formed Arabian head, with its jibbah0 and dish, is the combined result of the main support rod having little downward bend plus inflation of the frontal sinuses to form the bulging jibbah. Next month's article in this series will say much more about Arabian and Arabian-like heads.
The main purpose of this article is to familiarize you with the close relationship between the shape of the bones forming the horse's skull and the shape of the head in the living animal. Some things might appear on a horse's head that seem worrisome, such as frontal horns, a bashed-in forehead, or a wavy row of bumps along the lower margin of the jaw. But as the accompanying photos show, despite the fact that all of these derive directly from the condition of the underlying bones, none are normally great cause for concern. On the other hand, such subtleties as the symmetry of the head, the width of the ganache, and the overall quality of the skull are of paramount importance. Coming next: Jive on the Jibbah
A quality head has a wide ganache: The ganache is formed by the separation of the left and right branches of the mandible. Between them must fit the base of the tongue, the pharynx, larynx and upper part of the trachea, which underpin the important functions of swallowing and breathing. A wide ganache becomes particularly important in horses who are expected to perform with their head in a "tucked" position. (Photos by Deb Bennett, PhD)
A quality head is symmetrical when viewed from the front: A large number of horses have asymmetrical heads, and this defect unfortunately often goes unnoticed. When evaluating a horse's head, check to see whether the eyes are on the same level and placed equally far around to the left and right sides of the head. The asymmetrical horse on the right has one normal orbit and one facing downward and backward. The low eye continually "weeps" because of malformation of the tiny channel in the skull that forms the tear duct. The unevenness of this mare's head was made worse when she smashed into a fence post, but the reason she hit the post in the first place was her poor depth perception--the asymmetry of her orbits creates non-overlapping fields of view. It would be unreasonable, as well as unsafe, to ask a horse like this to negotiate jumps, trail obstacles or traffic. (Photos by Deb Bennett, PhD)
Component parts of a horse's skull: Once the parts are put together, the "main support rod" is not visible, but its position is evident in the see-through view at the bottom.
Internal view: The skull of an Arabian has been carefully sawn through from front to back, revealing an internal view of its actual structure. The flexure of its main support rod measures 7.8 degrees.
Convex architecture: The Mustang and Appaloosa have mildly convex architecture, while the Thoroughbred has straight construction. This, by the way, is another high-quality skull, showing great depth through the face and jaws. It belonged to the 19th century racing champion The Flying Dutchman. (Photos by Deb Bennett, PhD, and courtesy, The National Museum of Australia)
Concave architecture: Note that the pony's skull does not bulge in front of the orbits because there is no inflation of the frontal sinuses. The Quarter Horse--an individual who died recently--actually has a larger "jibbah" than the Arabian. In the Middle East, where the Arabian breed originated, large jibbahs are not particularly valued. (Photos by Deb Bennett, PhD)
Distinctive features: An American-bred Arabian mare (A); agrade horse from Canada (B); the author's part-Mustang gelding, Oliver (C). Oliver's arched facial profile is due solely to the downward flexure of the "skull's main support rod" within. While he has no inflation of the frontal sinuses, those of the mare at top are large. If her sinuses were added to the center horse, he would look like an Arabian; conversely, if they were removed from the Arabian, her head would clearly reveal the underlying concave structure that actually creates the "dish."
Lumps and bumps: This Andalusian stallion shows undulating bumps along the lower margin of the jaw. As the view of the jaw below shows, these bumps are due to the eruption of cheek teeth. Called "eruption cysts," the bumps are sometimes rather thin-shelled; if they are broken open, the tooth developing within will be killed.
To the point: Rarely, some horses develop "horns." These painless bumps directly under the skin are cold and feel hard and immovable. They may differ in size. "Horns" develop as a result of overactivity of cells in the fetus which produce the frontal bones. This photo also shows the hollow behind the horse's eye, which houses the coronoid process of the skull to which the temporalis muscles attach. The temporalis is one of two substantial muscles that move the jaws and help the horse bite down on its feed.
A hard knock: The author's mare Sadie at the age of 38. When she was 33 years old, Sadie got into a tussle with another mare who was wearing hind shoes with heel calks. The other mare kicked Sadie square in the forehead, crushing the right frontal sinus and creating a two-inch-deep divot. Skin quickly healed over the wound, and Sadie lived for years afterward. Such a mark may look alarming but is not grave unless the braincase itself, which lies behind the rear wall of the frontal sinus, is broken.
By Deb Bennett, PhD