The next common anatomical misconception in this series is about the horse’s back.
When people first see the location of the vertebral bodies within the horse’s back and also where the thoracic vertebrae themselves are positioned, it comes as a bit of a surprise.
In the first part of this series we looked at the location of the neck, which is another common misconception. If you’ve not read it – take a look at it - Taking the Mystery out of Equine Anatomy - Part 1: The Neck.
The thoracic vertebrae have very long spinous processes of bony projections which come out of the top of the vertebrae. When you're looking at these vertebrae just lying on a table, for example, it's difficult to always appreciate which bits go up and which go down. It is common for people to mistake these spinous processes for the ribs.
Our human back vertebrae are quite close to the surface, and although we have spinous processes in our thoracic and lumbar region, they're really very short compared to the horse. This is where the misconception comes from - when we look at a horse, we automatically assume that the thoracic vertebrae run along the top of the horse's back, and the ribs come straight out the side. In reality, if you look at the horse side on, the vertebral bodies are much lower down, with the spinous processes coming out vertically from the vertebral bodies and this is what creates the midline of the horse.
“When you run your fingers along the midline of the horse's back, what you're actually feeling are the tops of those spinous processes - not the thoracic vertebrae which are much lower down than many people think.” Gillian Higgins.
Moving from the neck to the back
The next question is how do we get from the low neck vertebrae to suddenly feeling bony projections at the top of the withers? The horse has 18 thoracic vertebrae – the first thoracic spinous process is quite short and they incrementally get longer. The longest spinous processes are of the fourth, fifth, sixth and seventh thoracic vertebrae, and these are what make up the withers. The first bony projection or spinous process that you can feel is the fourth one.
Position of the ribs
The ribs attach into the vertebrae at the level of vertebral bodies and it can be surprising just how low down they are within the horse’s back. This is another common misconception that occurs because we compare our body with the horse’s. Because we can feel our ribs on our back we then assume that the ribs are higher up in the horse’s back.
Looking at a cross section of the back, you will see a long spinous process coming out of the top of the vertebrae, and then either side, there are the ribs coming out from in between each vertebrae. This creates a sort of an upside-down T shape and the rest of the rib curves around the barrel.
When you are looking at the mid-section of the back right underneath where you sit, the ribs come out more or less horizontally from in between the vertebrae before they curve around the barrel of the horse. This means there’s a triangular shape, when we're looking at cross section between the spinous process, the ribs and the outer surface of the horse. That triangular shape is filled with muscle and the bulkiest muscle that fills that space is the longissimus dorsi.
Saddle Fit and the Horse's Back
The panels of the saddle lie on top of the longissimus dorsi muscle and the other muscles in that area, which are sitting on top of the ribs. Rather than thinking you are sitting on the horse’s back vertebrae, it’s the ribs that support your weight.
The width of the saddle gullet is an interesting thing to consider. If you look at the spinous processes on the horse’s back, they're actually quite narrow, but it’s important that the saddle doesn’t put pressure onto them - if there was no gullet, it would cause bruising over the area. That's why it's important to have a gullet in the first place, but how wide does it really need to be? If the horse isn't moving, it doesn't need to be very wide at all. However, as soon as the horse moves, the back will move relative to the body with each stride taken, and when the horse bends, the shape of the back and body changes even more so. Even when performing a 20-metre circle there is a certain amount of bend within the back and because the saddle doesn't bend we need to make sure that the gullet is wide enough so that in the majority of movements, the saddle panels don’t sit on the tops of the spinous processes.
“When you are riding on a circle, particularly on a small circle, the saddle will always naturally slip a little bit to the outside. Rather than thinking of the saddle slipping to the outside, think of the horse’s body moving underneath the saddle, so the positioning is going to alter.” Gillian Higgins.
Saddle slip
If your saddle is slipping to the side repeatedly, it can mean that the panels of the saddle are either sitting on top of, or just butting up next to the spinous processes on one side. If this is happening each time you ride it can cause tenderness or bruising in that area.
You can check the area for soreness by running your hand along the spinous processes and press on them from above or from the sides. There should be no reaction from the horse when you do this. If there is a reaction, you need to question whether the saddle slipping is causing the tenderness. This highlights the importance of having your saddle regularly checked by a qualified saddle fitter.
Saddle slip – horse or rider?
If you do have saddle slip issues, as well as considering your own symmetry, you need to question how sound the horse is. If you're not 100% sure whether the saddle slip is caused by rider or horse asymmetry, this simple exercise will help.
Ask a friend to film you.
Ride your horse down a centre line in trot away from the camera, this will give you a good view of how the saddle is sitting
Ride down the centreline off both reins
Repeat steps 2 and 3, but this time lead your horse from the ground down the centre line
Watch the video footage back and see if the saddle slips more or less with the rider on board.
If the saddle slips more without the rider, this is an indication that the saddle slip is caused by the horse’s asymmetrical movement.
If you see that the saddle stays fairly straight without the rider, but slips with the rider, this is an indication that the saddle slip is caused by the rider.
This is a really useful assessment that highlights where the issue is, giving you a clearer idea of where to look and what to do next.
How does understanding back anatomy affect the way we train and care for horses?
Having the knowledge about the correct anatomy of the back rather than the incorrect misconceptions, can affect how we feel the horse's back.
"You should feel your horse’s back on a regular basis, maybe as part of your grooming routine, or before or after riding. Doing this regularly gives you a valuable insight into what your horse's back feels like normally. Make note of what the muscle feels like, the tone, the condition, and is there any tenderness." Gillian Higgins.
On the Horses Inside Out Academy there is a FREE tutorial video called Test for Sore Muscles, where Gillian guides you through the process of checking your horse's back. This tutorial video is FREE to view for Academy members. If you aren't a member, head to the Academy and sigh up today (it's FREE to join).
Also, if you're interested in learning more about this, definitely check out the Horses Inside Out Online Massage Course for Horse Owners. This goes into detail on not just how to feel the muscles of the back, but how to assess the other structures, giving you the confidence to recognise if your horse is comfortable to be ridden.
Position of the Saddle
The other reason for appreciating the true anatomy of the horse's back concerns saddle fit and knowing where the back of the saddle should sit. If the saddle is put too far back, because of the change in the mechanics of the thoracolumbar junction, this can cause problems.
It’s important to understand the difference between the thoracic and lumbar vertebrae. Basically, what we're looking at is a change from the attachment of the ribs in the thoracic vertebrae which are mobile to help the horse breathe in and out.
Going back to the lumbar region, instead of a rib, there’s a fixed transverse process which comes out of the sides of the lumbar vertebrae. This means there is a mechanical change in the horse’s back at this point. If you press down on the muscles on top of the thoracic region, they'll squish up against the ribs, and the ribs will move a little bit. If you press down on the muscles in the lumbar region, you're pressing that muscle against the fixed transverse process, which is part of the lumbar vertebrae. So you'll get quite a different feel.
Thinking about the back of the saddle, the weight bearing part and the back point of the tree, if this is sitting on top of the lumbar vertebrae and the lumbar transverse process, it can create a pressure point because of the change in the mechanics of the back.
It's really important that horse owners and riders really understand where that point is on their horse and how to find it, so that we can make sure that we put the saddle in the right place, and make sure that the saddle that we're riding in isn’t too long, because that can cause discomfort in that area too.
Back Posture
The other reason for understanding the true anatomy of the back is that it can help us to achieve our goals and help the horse's way of going. As riders and trainers if we want our horses to work well over their backs, we really do need to understand the anatomy and biomechanics. For the horse to move in a correct way of going, they need to have good posture. In order to understand what good posture is, we need to know the anatomy the back.
Posture is a complete topic on its own. If you want to learn more about posture, you will find lots of great information about back posture in our on-demand online recorded webinar – Understanding Your Horse’s Back.
Also, have a read of a few of our previously published articles that we've written on back posture.
"All riders need to take responsibility for learning about equine anatomy. Horses do so much for us, we sit on them and ask them to carry us. I think it's up to us to take responsibility for their musculoskeletal health. We must take responsibility for their posture and conditioning, to make sure that they are in the best possible place, both physically and mentally, to be able to do the job that we're asking them to do."
Keen to further your learning about equine anatomy? Join us for a Live Painted Horse Lecture Demonstration at Moulton College, Northants on Saturday 21 September 2024 where you will quite literally see the horse inside out.
These demos are always great fun, educational and interactive. You will see your horse in a whole new light thanks to Gillian's anatomical paintings. Discover which exercises will boost our horse's comfort and way of going, and go home with a new found appreciation of how amazing horses really are.
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