Thorax one to eight are the sternmost vertebrae of the horse's cantilevered backbone. In their area is the greatest concentration of muscle. In the horse's elevation they rise. Attached to them are ribs one to eight. These ribs, via costal cartilages, connect to the sternum below. Vertebra, ribs and sternum form an elastic basket. It holds the horse's heart and lungs and protects them in rapid changes of speed, such as coming down from a jump. Like the eye of a storm, thorax one to four of this basket and the heart within are the center of equine animation.
Heart
Vertebrae one to eight extend into spinal projections, as do in fact all vertebrae of the equine backbone. There are no spinal projections of neck or tail. Beginning with a small bony extension at thorax one, these projection increase rapidly in size and strength, the strongest being thorax three. The longest projections, thorax four and five, represent the horse's height. Thorax five anchors the long ligament, which - coming from the occiput - runs through the upper line of the neck, and - topping each successive spinal projection - continues to the end of the sacrum.
Thorax projections four to eight support the equine shoulder mechanism. It consists of aerodynamically shaped shoulder blades and strong cartilages held in place by multiple layers of muscle and ligament tissue. These absorb the impulsion produced by a three levers mechanism in the horse's hindquarters. The shoulders are suspended by front legs, which in movement carry the horse's weight while touching down in perfect rhythm for always only split seconds. In the horse there are no collar bones and no joints between shoulder blade and vertebra.
Shoulders and arm bones are animated by three muscle groups. The pectoral connects shoulders, arm bones and elbows with the sternum. The latissimus dorsi via the thoracolumbar fascia proceeds from the arm bones to the back. It is anchored to the backbone between thorax eight/nine and lumbar two/three and pulls the arm bone back. This action is calibrated by two prominent muscles in the lower neck (brachiocephalic and omotransverse). From their attachments to the arm bones just above the elbows, they ascend to the upper neck and head and pull the arm bone fore, up and/or sideways. From atop neck and withers the trapezius connects shoulders and front legs with the back.
Shoulders
A study of deep muscles in the equine forehand points to a concentration of muscle to bone attachments along thorax projection five and the fifth rib under the highest point of the withers. This thorax five axis is situated between the before mentioned skin regions, which - like vertical strips along shoulders and front legs, connecting withers and front heels - indicate a dermatome C8 in the horse.
In the balance of the equine skeleton this thorax five axis corresponds with a muscular concentration around lumbar vertebrae two and tree in the upper part of the horse's Flanken. Along this thorax five axis upper, central and lower neck muscles meet with "...(the ventral serratus muscle system, which) bilaterally forms a sling suspending the trunk between (the shoulders). (They are responsible for) raising the trunk (Peter Goody)."
The ventral serratus muscle is a semi-circular muscle system, which proceeds between shoulders and ribs. Eight strands attach to ribs one to eight. Their attachments are found in the ribs' lower thirds. Four strands hook up to the sides of four lower neck vertebrae. In movement the ventral serratus muscle's punctual fixation to the inside of the upper shoulder blades glides, from a central place on the before mentioned thorax five axis, back and forth along the long back muscle. From this axis emanates as well the fix point of the rhomboid muscle to the shoulder discs.
Several, but not all functions of the semi-circular ventral serratus muscle are obvious. They raise thorax and lower neck, and - in the process - elevate the withers. They carry the weight of the horse's forehand and absorb the impulsion coming from the hindquarters. They maintain the shoulder's lateral balance. The role of the ventral serratus and the thorax five axis in the modern horse's new balance, however, remains to be researched further. It promises to be more than the sum of its physical parts.
It may be mentioned, that involved in the elevation of the forehand are flexions of jaw and poll. These flexions, via fascia trains, connect the balance functions of the hyoid bone at the root of the tongue with the underneath of second and third neck vertebrae and the lowest point of the before mentioned thorax five axis. From upper points of this axis muscles ascend to the occiput. Here also the free bearing long ligament of the neck transits to the thorax.
The elevation of the forehand is hindered by the modern horse's warp. Not the ventral serrate, which was spoken of, however, but another deeper muscle system, the dorsal serrate, plays a major role in irregularities of the forehand. The dorsal serrate also is involved when the horse bends. It will be discussed in context of the ribs below and in context of the German Rippenbiegung again in the next chapter "Flexibility".
Ribs
The horse's eighteen ribs are organized in sets of four. Laid out flat on the floor one notices their different shapes, sizes and curvatures. Ribs one to four are short and strong. With the vertebrae above and the sternum below they form the before mentioned three-dimensional forehold of the rib cage. Ribs five to eight also dock to the sternum. They underpin the shoulders. Ten remaining ribs (nine to eighteen) are free bearing. They hold the costal diaphragm from within.
Four ribs (nine to twelve) permit the horse to bend in what in German equestrian language is called Rippenbiegung. Four ribs (thirteen to sixteen) bear the rider's weight. The two remaining ribs (seventeen and eighteen) provide for muscular attachments to the hip bones, the widest lateral extension of the pelvis. Ribs twelve and thirteen are the longest ribs. They support the rider's seat bones, which are the lowest points of the human pelvis and impact the equine backbone at thorax twelve and thirteen.
Ribs connect to the left and the right side of vertebra one to eighteen. Attachments ribs to vertebrae permit the ribcage to move in all directions. Ribs can move fore and back. They can rise or descend. Directions of movement can be combined. The resulting mobility facilitates not only the horse's breath. It supports posture, position and movement. It accomodates the horse's body weight.
Several muscle systems move and/or stabilize the ribs. The iliocostalis or lower back muscle runs directly below the long back muscle. It spans the ribcage and connects the first ribs with the before mentioned concentration of muscle attachments in the lumbar region. The iliocostalis participates in longitudinal bending, which is initiated by the lateral setting of the head in the poll. It is a relatively straightforward system, which pulls the ribs back. The dorsal serrate, however, is part of a complex system, which blankets the horse's upper line including the lower back muscle from poll to croup. Intercostal muscles and the external abdominal oblique muscle balance the movement of the ribs in the horse's sides.
The sternmost part of the dorsal serrate begins at the before mentioned thorax five axis. It connects to ribs five to twelve and the intercostal muscles between them and pulls these ribs up. They rise to off-set the weight-bearing pressure on the shoulders. In conjunction with neck bending they release ribs five to twelve on the other side, thus uniting the bending of the neck and the release of the ribs. The dorsal serrate's rear part begins at rib eleven and proceeds towards the croup. It attaches from ribs eleven to eighteen and retracts them.
The space between the cranial and caudal dorsal serrate portions provides a place for the rider on the horse's back. Sitting there the attachment of the psoas to the inside of his upper thighs automatically impacts the overlap of the cranial and caudal dorsal serrate between ribs eleven and twelve. They as well impact the lower back muscle below at center. This point of impact calls for attention, for instance in the design and production of a modern saddle, which permits the rider's full contact to the horse's back and ribs.
The particular distribution of upper and lower rib managing muscles speaks for a distinct role of the rider's legs in the horse's locomotion. Not only do open legs permit the horse to move and closed legs restrict movement. One leg at the girth indicates the yielding of ribs under and before the rider's seat. The other leg behind the girth indicates the yielding of ribs behind the rider's seat. Via the dorsal serrate, the action of the leg at the girth corresponds with the action of the rein on the other side of the neck.
The rider's point of rest
The horse's warp represents problems. The leaning of thorax nine and spinal processes before as well as behind it create a three-dimensional irregularity in the forehand. The ribcage rotates right. The ribs of the right side are flat. On the left they bulg. The right front leg carries more weight. Energy lines coming from the horse's hindquarters do not match the rider's energy lines. As a result he can't be in full control of the horse.
Making the horse straight, however, does not necessarily change things for the better. The horse's sense of corporeality is challenged. Balance is at risk. As a result it tends to rush or hold back. Identity and well-being are marred. The horse is in doubt. Straightness, in other words, not only effects the body. It gravely impacts the horse's mind and emotions.
How does the rider best address the need for having a straight horse under his saddle?
The matter will have to be settled between hind legs, thorax, C8 and the poll. In this context the famous, if dated German Ausbildungsskala makes sense. It permits for the development of the horse's new identity on the basis of well regulated paces (Takt), a free flow of core energy (Losgelassenheit) and trust in the rider's hand (Anlehnung). Only after mobilization (Schwung) and elevation (Aufrichtung, which the Skala does not mention) will the horse be made straight (Geraderichtung). Only then it can collect (Versammlung).
The Skala, despite its fame, does not answer equestrian questions. Nor does it provide information for the horse's, leave alone the rider's training or how to deal with the modern horse's warp in the early stages of training. It says nothing about the choice of gait and/or tempo. It does not indicate at which point and in which context the horse profits from bending, nor does it elaborate on the two types of bending the horse. It makes no mention of self-carriage (Selbsthaltung) and permeability (Durchlässigkeit, or "the passing of body internal information in and between horse and rider").
Without these two concepts, however, no quality equitation exists. In addition the Skala provides no information on, for instance, lateral work and/or the reason for continued bending. It does not elaborate on physical needs and/or available exercises that might help the mounted horse be at its best. It makes no mention of best progressions in using them. It does not address the imperative not only to win the horse's trust, but to protect its motivation.
In addition, another widely accepted concept calls for trouble. Riding forward alone, without stopping, standing and work on the spot neither makes the horse straight nor light. Continued working trot or canter is not useful nor intelligent. In the long run it causes a loss of balance. The horse responds with a continuous flight into a balance, which forever eludes it. By contrast a new modern equitation calls for communication in the walk, while building up strength and mutual respect. It develops the flexibility of the haunches and prepares for the engagement of the psoas to assist elevation. it communicates in the stand-still. It permits for the stretching of legs, and air in the lungs, on straight lines in the outdoors. Free schooling and jumps are part of the fun. The true position, which in this text I call the second gear, is the standard of excellence.
In general application the rider uses the actions of reins on the neck and legs on the ribs to safe-guard the horse's lateral balance. He makes sure the horse's jaw yields to his ring fingers and the horse's ribs yield to the touch of his leg. He balances the touch of the inner leg with the action of a diagonal neck rein. A light contact to the mouth informs him of the horse's mental, emotional and physical state. He waits until both hind legs track evenly and enjoys the horse's elevation, which - as a result - it often produces sooner than expected. He knows how to assist the horse's elevation.
