The geometric shape of the silhouette is assessed by stopping the horse balanced on level ground, with fore canon bones vertically positioned.
Let’s imagine two vertical lines (Perpendicular to the ground) the first through the tip of the shoulder and the second by the hock when the hind canon bone is vertical.
The first horizontal line is the ground and the second will close the quadrilateral and is tangential to the top of the shoulder and the top of the croup (sacroiliac joint).
The shape obtained is usually a more or less elongated rectangle. Its height is measured at the withers and its length from the tip of the shoulder and up along the side directly above the hock when the hind cannon bone is vertical (for a hock "in place", it corresponds roughly to the point of buttock).
If the horse has hocks far behind, it has very prominent withers or very embedded, the rectangle may be slightly distorted.
The slope of the tangent line at the shoulder and the top of the croup will help to determine if the horse is uphill or downhill. If withers height is taller than the size at the top of the rump, the figure is uphill. If it is the opposite, it is downhill.
The length / height of the quadrilateral will determine if the shape is more "square" or "rectangular".
If the length / height ratio is below 0.96, we speak of a "square" shape (Fig. 1) until 1.03, it will be "squarish", and will become "somewhat rectangular" 1.04 to 1.10 and "rectangular "(fig.2) beyond 1.10.
In dogs, the Bulldog is "square" and the dachshund "rectangular".
If withers height is higher by more than 3 cm than the height at the top of the croup, the figure is uphill (Figure 3). It will become more or less uphill from 0 to 3 cm, and more or less downhill if the top of the croup is greater than 0 to 3 cm than the withers and downhill beyond a 3 cm difference.
Our Bulldog is "uphill" and the greyhound is "downhill".
The square or rectangular figure may be approximately evaluated at six to nine months after birth, and become more precise from the age of three years. The up or downhill side needs to wait for growth and can scale up or down until 5 or 6 years.
All of the skeletal and muscular chains ranging from elbow through the tip of the shoulder, withers, rump, and croup to the stifle are forming “bows” involved in the vertical and horizontal detent of the horse.
The shape of these bows plays a role in the magnitude of the steps (horizontal detent) and the ability to propel himself upward (vertical jump).
At equal muscle tone and flexibility, longer this set of bows will be, the more horizontal and vertical leap will be powerful.
Like a bow, the more it will be bent, it will be less powerful but least it will be bent, the harder it is to bend.
The more it will have its center of gravity backwards (horse uphill), the more it will help to push up, but it will require more effort to the hindquarters.
Conversely, the more it will have a front center of gravity (horse downhill), the more it will ease the effort of the hindquarters, demanding more shoulders effort (the "kick") and lowering the hips to provide the vertical thrust.
It is important to note that the training of young horses must consider their shape and evolution during the end of their growth.
In somewhat caricatured, we can say that a horse rather square and in fact uphill will have a less delicate balance to manage, especially for an amateur rider than a horse made a long downhill. However, this last one will have a better disposition than the first with long strides and a great trajectory, useful for top riders.
As so often in this book, it must be emphasized that the functional significance of a morphological feature is in interaction with other features.
It is almost impossible to predict the jumping ability by simply looking at the silhouette.
A long silhouette is a "plus" for flexible horse and tonic, and it becomes a disadvantage if he is stiff!
An uphill horse is an advantage if it has a powerful hindquarters and a disadvantage otherwise!
We see that the work plays a key role in the functionality of the silhouette. We do not work the same way a strongly rectangular horse and an extremely square horse, or an uphill horse like a downhill horse.
Apart from the amount of muscle and tone, the flexibility and the natural balance of gaits, the shape and size of the shoulder and croup and jumping technique are the parameters that interfere the most with the silhouette to produce expected results.
Note that all figures are found on the Grand prix paddock. From the "square" Jappeloup to the "horizontal" Touch Of Class and a Milton actually uphill to a rather downhill Electra.