Open the Horse's Thoracic Cage

impending danger and are responsible for the fightorfight response meaning that a wellfunctioning thoracic cage contributes to a relaxed and resilient horse.
Lets not forget about the sternum which is technically one bone made up of seven separate bones called sternabrae which connect by cartilage and then fuse. Because of the clavicle the human sternum also includes the manubrium the long flat bone that forms the front of the rib cage. In horses the lack of clavicle means the connection between their front legs and torso is muscular with the serratus ventralis thoracis pectorals assisted by the external obliques and brachiocephalicus acting like a sling and suspending the chest between the front legs and lifting the thoracic cage. If this mechanism is not working well the result can be a dropping of the torso and a sense of the horse being downhill on the forehand. 
Getting back to the sternum it can not surprisingly be negatively affected by pressure from a tight girth. The first eight ribs are attached by the costal cartilage to the sternum with the cartilage of the remaining ribs attached together to form the costal arch and connected to the cartilage of the eighth rib and therefore the sternum. In humans our last two ribs tend to be floating ribs with no cartilaginous attachments to the sternum but this tends not to be the case in horses and can be a source of discomfort.
The equine thoracic cage attaches to the spine through the 18 thoracic vertebrae. Youll feel the spinous processes of the vertebrae when running your fingers along your horses spine with the transverse processes buried under muscle tissue to the side of the spine. As you can imagine this area is susceptible to saddle fit issues particularly if the gullet of the saddle is not wide enough or if there are pressure points.
As riders we can often feel an issue in this area from the saddle. First if this region of the horse lacks mobility it may feel like youre riding the equine version of a piece of plywood on one or both sides or a freight train heading downhill. On careful observation you will notice the horse having difficulty standing square in the front a discrepancy between the two sides of the thorax or you will feel tension or reaction when you palpate around this area. Second if there is a problem here such