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Omohyoid
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David Genadek
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 Posted: Thu Oct 18th, 2018 05:24 pm
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Deb, I am at a loss as to why you would connect the Hyoid to the scapula with the Omohyoid muscle? Give me a clue.

DrDeb
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 Posted: Fri Oct 19th, 2018 07:02 am
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David, the Omohyoideus muscle connects the hyoid apparatus backwards to a point where it attaches to the fascia that enwraps the brachiocephalicus, i.e. functionally the omohyoideus attaches TO the brachiocephalicus. The brachiocephalicus then runs backwards and downwards to attach to the shoulder "area" (not the scapula, but rather to the humerus).

This rather peculiar arrangement (but then again, the horse's whole body is full of peculiar arrangements, isn't it) opens the possibility that the rider, pulling on the horse's head, is also pulling on its shoulders; and that the hyoid, caught between the two, can be sprained if enough tension develops.

'Enough' tension can occur, and I believe not infrequently does occur, when a right-handed jockey pulls the horse's head off to the right when, at the same moment, the animal happens to step with its left forelimb into a deep spot in the underlayment of the racetrack; or else for some other reason the breakover of the left forelimb is delayed. The tension developed from stretching the distance on the left side between the horse's muzzle and its left forelimb acts to also stretch the left recurrent laryngeal nerve, and this I believe is the usual cause of paralysis of the horse's vocal cord of the left side, a syndrome that horsemen refer to as "roaring".

When you read about the etiology of roaring in a veterinary book or magazine, universally they will cite the fact that on the left side, the recurrent laryngeal nerve loops around the aorta, which it does not do on the right side, and thus there isn't much slack or room for that nerve to be stretched. As you remember from anatomy class, nerves are composed of individual nerve cells having very long axons, and those axons cannot tolerate being stretched because stretching ruptures their cell walls and causes the cells to die. But the cause of roaring cannot, logically or probabalistically be merely due to this asymmetry in the anatomy, caused by the fact that the heart is not centered in the body but is usually found to the left side. Horses that aren't raced or ridden develop roaring with extreme rarity. Therefore, we expect the rider's actions must be a necessary element. The cause of "roaring", therefore, is not anatomical asymmetry but rider error, or at the very least, rider error combined with circumstance.

Hope this little review of what was taught in our anatomy class brings it all to mind again and makes it clear. -- Dr. Deb

Aloha
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 Posted: Fri Oct 19th, 2018 09:41 pm
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David, I was at the class in Bend too. I really appreciated lunch time!

Reminds me of what we said as kids, or what was the game?
The foot bone's connected to the leg bone. The leg bone's connected to the knee bone. The knee bone's connected to . . .

It should be so easy!

I googled and I think found this same drawing but couldn't get it to open up. Hope Dr. Deb will comment on it. I'm afraid to study it too closely yet.

DrDeb
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 Posted: Fri Oct 19th, 2018 09:44 pm
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David, you will recall that the horse lacks a collarbone/clavicle. Therefore, many structures that would relate to the collarbone/clavicle in the human have had to change their attachments, shrink, fork, or hook onto something else in the horse. The omohyoideus muscle in the horse, having lost its (primitive or original) relationship to the clavicle and scapula, now hooks onto the brachiocephalicus, a muscle which itself does not exist in the human -- the homologies of brachiocephalicus are not entirely clear, in fact, but it is probably a composite of several smaller muscles which exist primitively and in the human. So you should dispense altogether with trying to draw any direct comparison between human anatomy and horse anatomy; the horse's anatomy is greatly specialized and altered over the primitive condition, which is what is found (for the most part) in humans. Look in Sisson & Grossman for quite accurate and "officially accepted" information as to origin and insertion, as well as spatial relationships to other nearby muscles, of the omohyoideus.

I have deleted the image because it is inaccurate and confusing, and I don't want other readers here to think that's a drawing I would sponsor.

As to the names of the muscles, David you remember that a lot of the terminology of science is in Latin, Greek, or some hybrid of the two; but that you can also, perfectly correctly, call the name of a muscle in English. "Omohyoideus" is the Latin version; "Omohyoid" is the English version -- they mean exactly the same thing. -- Dr. Deb

David Genadek
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 Posted: Sat Oct 20th, 2018 01:51 am
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Thank You Deb!!

DrDeb
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 Posted: Sat Oct 20th, 2018 01:59 am
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This is Dave's post from two above; out of order because I couldn't get the "wrongly drawn" image of Omohyoideus to delete, so I had to delete the whole post. This is what Dave said:

"I have attached the drawing that got me confused. If you do a search for Omohyoid wiki says for a human It arises from the upper border of the scapula, and occasionally from the superior transverse scapular ligament which crosses the scapular notch, its extent of attachment to the scapula varying from a few millimetres to 2.5 cm.
For humans, the muscle is called the Omohyoid but in Sisson and 'Grossman for the horse it is called Omohyoideus. Is this a confusion between human and horse anatomy?"

Dave, at this point I'd also like to ask -- where did you get that drawing? Who is posting incorrect anatomy on the Internet? -- Dr. Deb

David Genadek
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 Posted: Sat Oct 20th, 2018 04:31 pm
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It was a facebook post from an equine Physiotherapist. I liked the attention the hyoid as so many of the horses that come in here have hyoid issues. I do question this statement: And the musculature that inserts onto them have a huge role to play in moving the tongue, forelimb protraction and scapulae ROM.

"So-and-so's" Equine Physiotherapy and Rehabilitation
October 15 at 6:14 AM ·
Arguably the most delicate bones in equine anatomy- the Hyoid Apparatus!

These bones provide anchorage for the horse’s tongue and larynx. And the musculature that inserts onto them have a huge role to play in moving the tongue, forelimb protraction and scapulae ROM.

Poorly fitted bridles- specifically tight nose bands and incorrect bitting, or restricted head/neck movement caused by bad hands or training aids will directly inhibit hyoid apparatus function, therefore affecting how your horse moves.

Symptoms of hyoid discomfort (which go hand-in-hand with TMJ tension) include; fussing with the mouth, drawing the tongue back, head shaking, unequal forelimb protraction and restricted shoulder movement to name but a few. Breakage of these bones can cause partial, or total tongue paralysis.

With this in mind, it’s quite logical to say that if these tissues are compromised then the horse’s whole musculoskeletal system will be compromised too.

DrDeb
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 Posted: Sat Oct 20th, 2018 10:29 pm
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David, scare tactics are a norm among certain chiropractors and bodyworkers. They do it because they believe it engenders business and more income for themselves. Sometimes it does do that, I think, because not EVERYBODY reads here, and therefore, not every horse owner is empowered by having correct information.

Yes, there is a connection between the hyoid apparatus and tongue and the forequarter, as I outlined in posts above. And yes, Francois Baucher in the 1830's was the first to teach this truth, that if any of the muscles that invest the pharynx and hyoid bones, or the tongue, are braced then there is no possibility of correct collection; just as there is no possibility of it if the muscles that overpass the poll joint are braced. This is because a brace in any of these muscles at the front end of the body tends to engender a brace through the loins; and if the loins are braced, then the horse cannot flex the lumbo-sacral joint and therefore also cannot flex the stifle and hock joints, and thus cannot "sit down" as necessary for collection.

Once again, and I have said this over and over again here: I love it when people see something questionable on the Internet and then write in here to get the straight dope. DO NOT BELIEVE EVERYTHING YOU READ -- just because something is printed does not make it true; and not every string of letters behind a person's name is valid. A lot of letter-strings are totally bogus. One of the most important jobs I have is to teach students of all stripes how to discriminate who they should be listening to. Cheers -- Dr. Deb

David Genadek
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 Posted: Sun Oct 21st, 2018 01:56 am
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Deb, How about a major role in forelimb protraction? That seems like a stretch to me.
I am having trouble getting things to post hence the duplications.

DrDeb
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 Posted: Sun Oct 21st, 2018 04:55 am
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David, the brachiocephalicus (the "composite" or "reorganized" muscle in the horse) is a large muscle and a major forelimb protractor. Humans, because our ribcage is not flattened from side to side as is the horse’s, and also because we do have collarbones, do not have “forelimb protractors” in the same sense as the horse. We do not have a brachiocephalicus; its nearest analog in the human (and it may in fact also be, at least in part, its homologue) is the sternocleidomastoideus, whose lower end attaches to the clavicle. As I mentioned previously, the omohyoideus in the horse has its posterior attachment to the brachiocephalicus. However, the omohyoideus is a very small muscle, either in the human or in the horse, and is not a major protractor of the forelimb. LOOK at the book, yes? All of this should be obvious from what is shown in S&G, or Goody's anatomy, either one.

Again: there is no reason to believe what is unreasonable. There is no reason to engage in discussions that are based on nonsense; it’s a waste of time and a major reason why I do not visit, or participate, in any type of “horse blog” other than this one. We are not responsible for correcting all the garbage that goes down on the Internet. What you can do, if you insist on continuing to read other blogs, is invite the people at those other blogs to come in here and ask their questions on their own.

Yes, sorry about the difficulty with the gateway; it's affecting me too. I don't know the cause and there's little I can do about it, except hope it clears up by itself. Cheers -- Dr. Deb


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