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Piriformis muscle
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Dorothy
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 Posted: Sun Oct 4th, 2015 09:27 pm
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Hi Dr Deb,
I am wondering about the piriformis muscle in the horse. I can find very little mention of this muscle in my various anatomy texts. In one it is illustrated, but is very different to the piriformis in a human, and the same muscle is named the gluteus profundus in a different text.

Please can you tell me if the horse does have a piriformis muscle?

Thank you
Dorothy

DrDeb
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 Posted: Tue Oct 6th, 2015 09:10 am
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Dorothy -- you don't have a copy to hand of Sisson & Grossmann's "Anatomy of the Domestic Animals"? Better get one -- I recommend any edition between 1920 and 1970 -- what you want is the old one-volume book. It will cost you around $50 to $150, depending on the condition it's in.

Anyway, I quote: "Piriformis -- is not blended with the gluteus medius. It arises from the border and ventral surface of the sacrum and from the sacro-sciatic ligament, and ends on the trochanter major (of the femur) with, or close to, the gluteus medius."

The above description is taken from the DOG section of the book, and there is no mention of piriformis in the HORSE section, not even as a subportion of the gluteus superficialis. I however have seen a subportion that could justifiably be called a piriformis in some dissections; it is not there in others. The piriformis we therefore conclude, like quite a few other muscles in the horse, is being vestigialized.

So that's the authoritative word on the subject. What actually brings you to ask (I can't believe it's just the contrary opinions of people you've asked). Are you trying to pass some kind of test? Cheers -- Dr. Deb

 

Dorothy
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 Posted: Tue Oct 6th, 2015 10:38 am
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Thank you.

No, I'm not doing any test, but I was looking in my books with reference to another matter, and noticed that piriformis is not mentioned or illustrated in any of them (except the one where it is illustrated, but I don't believe that that actually is piriformis).

It sparked my interest because of the importance of piriformis in the human, not least because of its anatomical association with the sciatic nerve. In some people the nerve runs over it, in others under it and in others through it. Piriformis muscle tightness is implicated in many cases of 'sciatica'.

I have rather taken myself by surprise here in that I have not noticed the lack of piriformis in the horse before now in spite of having worked as both a human and equine chiropractor for many years. In all these years I have never heard anyone refer to piriformis in the horse, or problems related to it. If it is becoming vestigialised then that would be why.

Dorothy

Dorothy
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 Posted: Tue Oct 6th, 2015 04:01 pm
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Whilst I don't have a copy of Sisson and Grossman (something that I need to rectify!), I do have a reproduction of the 1683 Edition of Andrew Snape's 'The Anatomy of an Horse'

Snape does describe the 'Pyriformis - or pear- like muscle' 'arising round from the lower and outer part of the Os Sacrum; thence it runneth downward on the backside of the great Rotator, and is implanted into the outside of the lower end of the thigh bone'.


DrDeb
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 Posted: Tue Oct 6th, 2015 07:57 pm
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Dorothy, Snape is an antiquity and a curiosity; not to be used in any serious context as it is far out of date, and full of errors. Note his idea of where the insertion is; sounds like he's actually describing the femoral biceps. Go with S & G, that's the no. 1 modern authority. -- Dr. Deb

Dorothy
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 Posted: Tue Oct 6th, 2015 08:06 pm
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Yes, I do consider Snape to be amusing rather than authoritative. I do like the language though.
Dorothy


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