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False rib, floating ribs, ribs?
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CarolineTwoPonies
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 Posted: Sat Mar 5th, 2011 09:08 pm
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Dear Dr. Bennett,

I recently looked a new saddle on the market and one of the selling points was that it is designed to sit forward on the horse so as not the impede the action of the loin by interfering with the "floating" ribs of the horse which were described as not attached. I questioned what was meant by not attached and I was sent to check a book which used the word "floating" ribs for the last 2 ribs which are shorter and only connected at the bottom by connective tissue or cartilage. In looking around I also saw the word "false ribs" used for these ribs which are not attached to the costal arch. Is the costal arch the same as the sternum?

My question is: Does the fact that the ribs are not attached at the bottom make a difference at the top of the spine/rib attachement?. Are these ribs attached differently to the spine, with less intercoastals, less of a network of muscles then the other ribs? I sometimes get hold up by words, and floating indicates a lack of solidity through the entire rib where in fact it seems these ribs are more flexible.

I also run into the words: supernumerary ribs, does that address the case when there is a 19th rib? When there is a 19th rib, it is attached differently?

I am not arguing for saddles to sit back, just curious about the rib structure.

Last edited on Sat Mar 5th, 2011 09:13 pm by CarolineTwoPonies

DrDeb
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 Posted: Sun Mar 6th, 2011 07:23 am
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Caroline, honestly, the amount of bogus "anatomical information" put out by various saddle-sellers is just astonishing. But, of course, the only reason they can get away with spouting garbage is that they are just that little bit more knowledgeable than the majority of people they aim to sell to. You, at least, along with all the others who read here, are at least interested and motivated to find out the real facts.

Of course, the whole thing would be easier, and probably save you some trouble, if you would just go out and purchase one of the readily-available horse anatomy books. There are two I'd recommend as first purchases: either get the one by Goody, entitled "Horse Anatomy", published by J.A. Allen. Be sure you get the revised 2nd edition, which is the latest version. The other one is Chris Pasquini's "Atlas of Equine Anatomy". Both books are printed in black and white, and for this reason are relatively inexpensive.

As to your specific question, which boils down to "what is a 'floating' rib": This is a layman's term borrowed from human anatomy. People normally have 12 pairs of ribs, of which the last two lack costal cartilages, which are the thin rods of cartilage that connect the terminal tip of the rib back to the sternum. Because the 11th and 12th ribs are not connected to the sternum, but only to the corresponding vertebrae, they are termed "floating".

Horses are quite another species, with very different locomotor capabilities and thus a very different design to the thorax. Horses normally have 18 pairs of ribs, one of the largest numbers of ribs among mammals. All of their ribs, even the last couple of pairs, have costal cartilages which connect forward to the sternum. Horses therefore have no "floating" ribs.

Likewise, in the horse, the intercostal musculature is uniform from front to back; the intercostal muscles are similar between the first and second pairs of ribs and between the 17th and 18th pairs.

As to the saddle design itself, I assure you that all correctly-designed saddles seat the rider as far forward as possible on the thorax. How far forward is "possible" varies from horse to horse, because what limits how far forward the saddle can rightly be placed is the height of the withers and the degree to which their height carries back. The object in all good saddling is to get the rider's weight as close as possible to the stiffer (and thus less oscillating) parts of the thorax, i.e., as close as possible to the withers. This leaves the rear part of the thorax freer, and the loinspan completely free, to oscillate as they need to for the horse to collect, bend, and step laterally, as his work may require.

Dave Genadek tells sad, sad stories about debates that go on elsewhere on the Internet, where one saddle-maker says that the saddle should sit over the 14th thoracic, or perhaps the 17th, because the writer is trying to describe the anticlinal vertebra. The problem is, none of these folks has really had the advantage of being taught anatomy by someone who is qualified to teach it. Thus they struggle, and the concepts and ideas they then put forth are muddy or garbled or wrong.

I'm all in favor of saddle-makers everywhere learning horse anatomy. I just wish more of them besides Dave would show up in my anatomy classes. Why -- it would even be possible for a group of saddle-makers to EMail me and tell me that they would like to underwrite an anatomy class geared just to their particular concerns. As could a group of farriers, a group of horse trainers, or a group of interested riders. Really. It would not be that hard. I've got several specimens in the lab freezer right now. All we need to make the lid to the freezer fly open is....interested and committed students willing to travel to the class and split, among them, the teacher's fee. -- Dr. Deb

CarolineTwoPonies
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 Posted: Thu Mar 24th, 2011 06:18 am
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Is there a difference between how the first 9 and the last 9 pair of ribs are attached to the spine?

DrDeb
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 Posted: Thu Mar 24th, 2011 06:34 am
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No, not really; the ribs diminish in size and stoutness from front to rear. There are slight changes in angulation or the 'aim' of the rib as it diverges from the vertebral chain. These changes are little, and cumulative, so that the fore ribs come off nearly at 90 degrees to the spine, while as you go to the rear, more and more they angle back. At the very rear they are still coming off at 65 degrees or so, so over 18 changes you don't see very much difference from one attachment to the next one back. -- Dr. Deb

CarolineTwoPonies
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 Posted: Thu Mar 24th, 2011 06:47 am
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Thank you for your help in understanding this. I have a couple of anatomy books and I could see that all the ribs look as though they are attached the same but I could not find text about how they attach.

DrDeb
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 Posted: Thu Mar 24th, 2011 10:19 am
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You can review the 'Racinet's tri-dimensonal law' thread and look at the top view of the horse skeleton that I posted there. This view shows the ribs all in the 'forward' position, i.e. as if the horse were frozen in the act of inhaling. When the horse exhales, the rear ribs flatten down 20 degrees or so.

There are also some pictures in the thread that show the costal facets, where the twin heads of each rib actually attach to the vertebrae. -- Dr. Deb

CarolineTwoPonies
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 Posted: Thu Mar 31st, 2011 06:33 am
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Thank you Dr.Deb. I took a shot of a skeleton last week:

Attachment: 192653_10150243000594988_695629987_9317256_7069509_o.jpg (Downloaded 131 times)

DrDeb
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 Posted: Thu Mar 31st, 2011 07:22 am
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Right, Caroline. And can you tell me -- what's wrong with this skeletal mount? The MAJOR thing that is wrong with it. -- Dr. Deb

CarolineTwoPonies
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 Posted: Thu Mar 31st, 2011 07:28 am
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Are some of the middle vertebras facing the wrong way? 4, 5,6,7,8 and 9 look like lumbar vertebras rather then thoracic vertebras but I have not seen a good skeleton is a while. I am counting from the tiny piece at the top of the screen. I just thought it was old and wonky I did not think beyond that (DUH!)

Last edited on Thu Mar 31st, 2011 07:36 am by CarolineTwoPonies

DrDeb
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 Posted: Thu Mar 31st, 2011 07:52 am
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Caroline, how do you tell a lumbar vertebra from a thoracic vertebra -- absolutely impossible to miss the difference, if you know it. -- Dr. Deb

CarolineTwoPonies
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 Posted: Thu Mar 31st, 2011 09:42 am
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According to the one book I have with pics, lumbar vertebras have a longer wing span to their transverse processes then the thoracic vertebras so the answer is not that it is a misplaced section of vertebras.

I had to edit again because I looked at the Ring of Muscles paper which shows a topline and comparing it to the one above now I am not sure anymore that there is a misplaced vertebrae, the spacing between them still looks wrong but I dont have anything concrete to base that on.

Do you recommend a book that shows real bones and skeletons? I looked at a book called "Equine Back Pathology" published by Wiley-Blackwell but I am not connecting the dots.

Thank you for your help.

CAROLINE -- Thoracic vertebrae have no "wings" at all. Their transverse processes are tiny. The transverse processes of lumbars are formed as large wings that extend out to the side. The ribs ARTICULATE with the thoracic vertebrae, and are what 'stick out to the side' in the thoracic span; the transverse "wings" that stick out to the sides in the lumbar span, are PART OF the lumbars. -- Dr. Deb

Last edited on Thu Mar 31st, 2011 09:28 pm by DrDeb

Ola
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 Posted: Thu Mar 31st, 2011 01:55 pm
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Hmm as for a wrong part with this skeletal mount - I think that in a normal position of standing horse thoracic vertebrae are curved downwards when you look from the right to the left. This slightly upward angle of thoracics looks really extraordinary. I wonder what on Earth this horse could be doing, as I think it's anatomically impossible to lift the base of the neck SO high :-) Am I right? Dr Deb, you asked about the major fault with the skeleton, so I guess there are also some minor ones? If so, what are they?

HorseSpeak
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 Posted: Thu Mar 31st, 2011 04:48 pm
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DrDeb wrote: Right, Caroline. And can you tell me -- what's wrong with this skeletal mount? The MAJOR thing that is wrong with it. -- Dr. Deb

Since Caroline answered this one already I'd like to share what I am wondering about...are the second and third vertebrae from the right hand side of the picture transposed?  (I am looking at the shape and height of the spinous processes.)


NO -- Dr. Deb

Last edited on Thu Mar 31st, 2011 09:29 pm by DrDeb

Dorothy
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 Posted: Thu Mar 31st, 2011 05:07 pm
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I may be being very stupid about this, but, if the furthest left hand spinouses are on the 'downslope' of the withers, I don't think that all the thoracic vertebrae are present. My guess is that there are only 15 or 16 maximum.

Also it is mounted with the spine in a downward arch, rather than an upward arch.

Dorothy


RIGHT -- on both counts. I also think there might be one or two posterior thoracics missing from this mount.

RIGHT -- the MAJOR problem with the mount is that the line formed by the centra sags downward instead of having a slight upward arch. All normal horses stand at rest with a slight upward arch through the freespan of the back. Note that it is the LINE OF THE CENTRA -- not the topline -- that we are speaking of. -- Dr. Deb

Last edited on Thu Mar 31st, 2011 09:31 pm by DrDeb

CarolineTwoPonies
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 Posted: Thu Mar 31st, 2011 06:08 pm
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Dorothy wrote:
I may be being very stupid about this, but, if the furthest left hand spinouses are on the 'downslope' of the withers, I don't think that all the thoracic vertebrae are present. My guess is that there are only 15 or 16 maximum.

Also it is mounted with the spine in a downward arch, rather than an upward arch.

Dorothy



There are 18 thoracic vertebraes for 18 pairs of ribs and in this pic you cannot see the first ones which you can glimpse in front of the shoulder. The shoulder obscurs the bodies of some of the ones with the longest spinous processes.

Now I am looking at the ribs and thinking they look wonky as well, there is no progressive arch and harmony in the cage formation.

Its easy to see a flaw with everything.

Caroline -- if you are right there and have actually counted to be sure there are no thoracics missing, then this animal had an exceptionally nice set of withers that "carries back" quite far. Very desirable conformational feature that is.

Yes, it is easy to see what the major flaw with the mount is, the lack of arch through the whole freespan.

Now I'm going to ask you: what is the next-most obvious problem? There IS definitely a bone missing from the mount. What is it?

Last edited on Thu Mar 31st, 2011 09:33 pm by DrDeb


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