Science Interviews


Sun, 20th Dec 2009

Dissecting Christmas Dinner

Dr John Brackenbury, Cambridge University Vet School

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John -  Now, the result is a lovely tasting bird but the muscles are completely useless for flying.  Itís just too big.  Itís lost all its natural strength.  And itís only good for eating.  Now, the other one we mentioned, the deeper one, thatís used for the up stroke.  So that does the opposite movement.  When a bird wants to beat its wings back up but after the down stroke, it uses that smaller one.

So these are two pectoral muscles.  (c) TreblRebl@Wikipedia" alt="Roast Chicken" />And theyíre used in flying.  Now the other thing that weíve exposed by separating the meat along the midline, very easy to do, are several things.  First of all, right in the midline, and if your Christmas listeners are doing this, youíll see a ridge, a ridge of bone.  Actually in this chicken, itís a ridge of cartilage.  It should be bone.

Helen - Oh, right.

John -   But nearly all chickens are slaughtered so early in their lives, all of them.

Helen - So actually because itís young, it hasnít become bone yet.

John -   Exactly.  Itís not yet trying to turn into bird.  

Helen - Right.

John -  So itís just gristle.  So thatís one thing.

Helen - Almost up to where the muscles are attached to.  Is that why itís there?

John - Thatís where theyíre attached to.  And thatís why it is so deep.  Itís actually about two centimetres deep because this great big great muscle is attached into it.  But anyway, thatís one of the things we could see in the midline.  Now if we move towards the front, towards the neck of the chicken, we see something else which everybody well know: that is the wishbone.

Helen - Right.  That V-shaped bone.

John -  That V-shaped bone right at the front.  In fact, technically, this is called the little fork or forcula.  I mean, it is a fork.  Itís shaped like a fork.  Anyway, thatís one of two sets of collarbones the birds have.

Helen -   Oh, so this is the bird's collarbone.

John -   Thatís right.

Helen -   Right.

John -   Thatís the little collarbone.  And actually, it doesnít do much.  But deep down under that second layer of muscle I mentioned earlier is a second set of collarbones.  These are much stronger.  And theyíre essential for flight.

Helen -   Is there two collarbones because thereís two sets of muscles?

John -   There are two collarbones because the wishbone itself is a bit of an apology.  It wonít really do the job, which any flying bird needs to, which is to stop its shoulders crunching towards its breast when it makes a powerful beat.  And the function of that deeper collarbone is to stop that happening.

Helen -   So would we get an even better wish if broke the inner collarbone?

John -   I knew we would.  You would be.  It takes a bit of getting to.  And I think by then, youíll be so tempted to eat this thing that I think you would have forgotten the functional aspect.

Helen -   Well we certainly  are getting into the grips of this chicken.  And if we were looking at a turkey, would it be very different, or would it have a structurally very similar once you get inside them, or goose, or a duck?

John -   Yeah.  There are differences, many on accounts of size.  Now the turkeyís going to be very similar to the chicken whereas the goose is going to be quite different.

Helen -   Right.

John -   The turkey and the chicken have white meat.  It has a distinctive taste because itís full of something called glycogen.

Helen -   And thatís what makesÖ So we have white and red meat.  Is that right?

John -   Thatís right.

Helen -   Yes.  Why are those different?


Theyíre different as I say, the white meat has glycogen.  And theyíre tend to be used when a muscle beats very quickly but exhausts very quickly as well.

Helen -   So itís for a very, very fast moves.  Right.



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