Monthly Archives: January 2018

Here’s my horse’s leg!

So having acquired a horse’s leg, what do you do with it?

Ignoring some of the cruder suggestions that I know some of you are thinking (yes, I mean you Bill), here’s how I use it in lessons with my Year 11s/12s…

I start the lesson with the story I wrote last week. It’s a good introduction for what follows, if only because it grabs their attention. Huh? here’s this going?

I then ask, what have we got in common with horses?

It doesn’t take much prompting to unleash a deluge of similarities – we’re both animals, both mammals, have two eyes and ears, a mouth, a nervous system. We have a digestive system and a back bone…

Ah! Yes, both vertebrates. And, in fact, both possessors of a fine skeleton.

What do all these points tell us about our respective family trees?

Again, they’re very happy with the idea that at some point in the past, we shared a common ancestor. Which is why we both have, for example, legs….

I fish out the first bone. It’s a whopper. Which leg?I ask.

For some reason, they always think it’s the back leg. But no, it’s actually the front.

Which brings me to the Curious Incident of the Badger in the Night. Because ideally I would not start with the enormous horse humerus, but the horse scapula, because it’s so glaringly obvious what it is and so glaringly similar to our own scapula, that great flat sheet of bone for powerful muscle insertion. It’s perfect for setting the stage of homology, which is of course where this is all heading, as it establishes more clearly than any picture or discussion that their bones are our bones.

So why don’t I have one?

Well, I did. The leg so generously deposited on our drive all those years ago was in full possession of a scapula, and a scapula was certainly deposited, along with all the other bones, into the dustbin of horse-stock that I described last week. But at some point in the Neutrase X-tremo-Stench digestion that followed, some wretched animal –that must have found the smell appealing… – found the dustbin, nosed off the lid, and made off with the top-most bone, a nice juicy scapula. A badger? The neighbours’ dog? We’ll never know. And I never found it, despite extensive searches. Grrrrr….

Still, it adds another nice little detail to the story – they think it’s funny – and we’ve established, via a rather roundabout route, that this is a horse front leg. We’re also standing next to the lab human skeleton.

OK, if this bone was attached to a horse scapula, what is it? What’s the equivalent bone in a human?

Yes, that’s right, it’s a humerus. How are they different? And why?

horse leg 1

It’s a striking contrast. The two bones are pretty much the same length, but the horse one is massively thicker and heavier. Of course it is. Horses don’t use their front limbs for swinging through the trees or picking fruit or grooming other horses. They need load-bearing supports that can hold up half a tonne of equine beast.

OK, if this is a humerus, what’s next? They generally know their skeletal anatomy – yes, we should have a radius and ulna.

Quick aside – which one’s which? This they don’t know. Or just guess. There are groans for my handy aide-memoire – the ulna articulates with the ulbow, while the radius articulates with the rist.

horse leg 4

So what’s going on here? Because the next horse bone seems to bear no resemblance whatsoever to the human equivalent. It appears to be a single, massive load-bearing bone again.

horse leg 7

But wait, look more closely. There are two bones, one articulating with the ulbow, the other with the rist, but they have fused together. It’s a beautiful illustration of the line from the Evo-Devo song – “safer the mutation aimed at regulation, keep the building blocks but switch their activation…”

It’s almost my favourite moment. As evidence for a shared ancestor, it’s compelling. As evidence for evolution itself, it’s hard to beat. No divine creator would make such a bodge job if designing the thing from scratch. The students think it’s seriously cool. Look! A horse embryo develops exactly the same bones that we do, and then glues them together because it actually only needs one, and for a completely different function.

But it gets better. If the broad base to this bone makes it the radius, what bone should come next? A quick cross-check with the human skeleton, and they realise it’s the wrist, not just one bone, but lots, the carpals.

horse leg 2

And here they are, a really pleasing set of bones with an intriguing jigsaw puzzle for anyone sufficiently interested and motivated to try and piece them together.

But how odd! The horse’s wrist is half way up its leg. Again, only evolution can explain the idiocy of having a cluster of blobby bones half way up a load bearing limb. Intelligent design? Give me a break…

On we go. What’s next? The finger bones! The meta-carpals! Again, something seriously weird is going on.

horse leg 9

There only seems to be one meta-carpal, but look closely and there are the others, shrunk and withered and, again, fused either side of the central one.

horse leg 8

We put them out in order, ending with the pleasingly shaped “hoof-secreting” bone.

horse leg 3

horse leg 6

And I ask them to demonstrate their understanding by giving me a simply visual indication of what a horse runs around on. … Yes, that’s right. It’s their one and only chance at school to safely give their teacher the finger…

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Where’s your horse’s leg?

When I first became Head of Biology at Oxford High, I had a poke around the department and eventually had to ask:

Where’s your horse’s leg?”

“We don’t have a horse’s leg.”

“What do you mean, you don’t have a horse’s leg? You must have a horse’s leg! You can’t teach biology without a horse’s leg! Where is it?”

“We don’t have a horse’s leg.”

“You don’t have a horse’s leg?!?!?!?!?”

“We don’t have a horse’s leg.”

I was shocked. It seemed that they didn’t have a horse’s leg.

Oh well, I thought, that’s quickly rectified, and I started hunting on line for horse legs. By which I mean the bones of a horse leg. This proved harder than I anticipated. None of the educational supply companies stocked horse legs. I eventually found one company that could supply an entire horse skeleton for about £3000, but nothing remotely resembling a single horse leg. Ebay, Amazon, horsesleg.com, all came up short.

I rang the Natural History Museum in Oxford. They were lovely!

“Have you got a horse’s leg?”

“Yes, we’ve got lots.”

Hallelujah!

“Can I have one?”

“Sure. To borrow.”

“Oh. I want to keep it. Can I have it on permanent loan?”

“No”.

Damn! It was back to the drawing board.

So I had a think, and decided to track down people who made a living preparing specimens for museums. There aren’t that many… But I eventually made contact with a chap who had lots of good advice. I would need a container for the specimen that could be filled with water and heated – a saucepan or similar. I would need a thermostatic heater. I would need water. And I would need Neutrase

http://www.ncbe.reading.ac.uk/MATERIALS/Enzymes/neutrase.html

a powerful protease that works best in neutral (hence name) conditions…

Oh, and I would need a horse’s leg.

This last detail seemed a bit of an obstacle, but it proved far easier to source than I imagined.

New to the Oxfordshire area, we had been invited to a lunch party to mingle with local folk and maybe make some friends. I ended up chatting to a man who described himself as a Trainer and Breaker. Of what? Why, of horses, of courses….

Ta da!!!!!!

Well into the second bottle of lunchtime champagne, I said casually,

“these horses you break and train, do they ever, um, die….?”

“Yes, all the time. They break a leg or get an infection or can’t run anymore and they’re put down.”

“Um, the next time, um, one of your horses dies, um….”

“Yes?”

“Can I have a leg?”

He was brilliant. He didn’t bat an eyelid. Yes, of course I could have a leg. No problem at all. Front or back?

I told him my preference, gave him my contact details and we parted on good terms.

The very next morning the phone went at about 6am.

“Were you serious about wanting a horse leg?”

“Yes, absolutely!”

“Because we’ve just had one die. Shall I drop it off later this morning?”

“Yes please!”

Long pause.

“It was rather a big horse…”

I didn’t want to let the moment slip.

“I don’t mind! I’ll take it!”

And so just a little later that morning, my wife opened the curtains to look down at our yard, to see a scene like something from the Godfather – a large hessian sack, containing a freshly hacked off horse leg, bleeding profusely into the cobblestones…

He hadn’t exaggerated. It was huge! Nearly as tall as me, and I’m only just under 6′. It must have been a monstrous great thing.

But, key question, how do you set about dealing with a freshly severed horse leg?

First step, remove as much of the flesh as possible. I was sent to the bottom of the garden where I was able to suspend the leg from a tree with bailer twine and use the large kitchen knife to carve off the skin and muscle. This was pretty gruesome and I filled a wheelbarrow with horse meat. A nearby sett of badgers enjoyed a free feast that night…

I now had lots of bones, still held together with scraps of connective tissue and all covered with small bits of meat and tendon. I disarticulated the main bones and put them all into a large metal dustbin I had bought for the purpose. In the larger bones, I drilled a couple of holes…. I then built a little bonfire under the dustbin and heated it to just below boiling. This melted all the fat, particularly the marrow fat which drained from the holes, and formed a disgusting scum at the top of the dustbin….

I dug a hole in the ground to pour the waste water into, refilled the dustbin with fresh water, added the Neutrase and inserted the thermostat, set for 40’C…. and left it for a week.

Oh lordy lordy the SMELL! It was AWFUL, gut wrenchingly HORRIBLE, quite the most disgusting olfactory experience I have encountered. The resulting dustbin soup resembled something they might serve in Hades.

But after a week, as per instructions, I was able to pour off this liquid to be left with…

my long awaited horse leg bones!

horse leg bones

Now why, the patient reader might be wondering, had I gone to all this trouble? What is the educational value of a horse leg?

For that, you’ll have to tune into my next post where I’ll describe that lesson … along with the Tale of the Curious Incident of the Missing Scapula….

thanks for reading!