What is an arm and what is a leg?

andy · April 2006

This has been bothering me for some time.

What makes an arm an arm?

For example, a horse has got four legs, but humans have got two arms and two legs.

So what about bears? Have they got arms or legs? What defines a limb as an arm?

It's really been troubling me.

David · April 2006

It troubled me too once you brought it up. I've come to the conclusion that they're defined by their use. A leg is a purely supporting limb, an arm is more a useful limb for climbing or picking things up. But does that then mean that Bears have arms and not four legs?

Liz · April 2006

This is the best discussion thread ever. Maybe if they're used primarily for walking on, they're legs, but for two legged animals the other two are arms (monkeys, kangaroos, etc).

Also, Andy, you might enjoy this (for anyone who doesn't know, Andy is a font geek)...

The arm of a letter is the horizontal stroke on some characters that does not connect to a stroke or stem at one or both ends. The top of the capital T and the horizontal strokes of the F and E are examples of arms. Additionally, the diagonal upward stroke on a K is its arm. Sometimes arm is used interchangeably with bar or crossbar or cross stroke.
Arm is often also used to describe the mostly horizontal top stroke of C, double-storey a, G, and other glyphs, to include the finial, terminal, spur, or other elements of the stroke.

andy · April 2006

But Gorillas, Orangutans and Bears walk on their arms. If, indeed they are arms.

And anyway, 'not walking on it' is a negative definition, I think.

It's a bit like 'not having feet'.

I think I want a definition of arms that allows gorillas, bears, humans and tyrannosaurus rexes to have arms.

It's got to be something about hands, I think.

(i did enjoy the font diversion too)

andy · April 2006

Bears are the ones that throw a spanner in the works.

David · April 2006

Not sure it is a negative definition. Both arms and legs can support the body but legs are solely support whereas arms can *do things* too. Also, bears don't really do that much with their arms do they? Swiping at fish is about it isn't it? So maybe they just have cool front legs.

andy · April 2006

Maybe that's it. Arms are legs that have got hands on the end, instead of feet.

Though I fear all we've done is shifted the terms of the question....

Lucy · April 2006

bears dig into bees' nests for honey with their paws, and they pick berries. Very dextrous.

Liz · April 2006

Lucy, great contribution - always guaranteed to know random facts about wildlife. It sounds as if there are probably three kinds of limbs - legs, which are just for walking; arms, which are not for walking at all; and limbs that do both. BUT WHAT ARE THEY CALLED THEN?

andy · April 2006

No. There's no room in this definition for a third thing.

It's simple enough, you just have to draw a line between arms and legs. The third category just described the grey area between arms and legs. It's not (I don't think) a distinct third category.

So what you have to do is decide whether your definition of arms is 'strict' or 'loose'.

A strict definition of arms only includes humans, t rex and maybe orang utans - the 'not for walking at all' definition.

A loose definition includes the strict definition, plus the 'grey area' - legs that you walk on but that have hands/paws on the end for opening jamjars and killing bees and stuff.

Then legs are still legs.

Lucy · April 2006

orang utans do walk on all fours, although mostly they swing from tree to tree. Ooh ooh ooh, I wanna be like you-ooh-ooh...

Surely chimps, gorillas and other apes have "arms" rather than "legs" even if they do walk on them? We don't say that crawling babies don't have any arms. I don't think the strict definition's a goer.

David · April 2006

Also, you've got the whole kick versus punch thing, which I presume gives legs a strict and loose definition too.

andy · April 2006

What's the kick versus punch thing?

Is that a perfect subset of arms and legs?

David · April 2006

well I was just thinking that a kick is not an act of supporting the body, and therefore a leg doesn't solely support the body.

andy · November 2006

For our new members, I have decided to revive this thread to demonstrate the high quality levels of debate that can occur on this site.

I still don't feel I know the answer to this question, particularly in reference to bears.

David · November 2006

There must be a term out there. Something like _ambidextrous_ but instead of interchanging left and right, its interchanging use of arms and legs for certain actions. Maybe we can invent one if there's not one. Bears and Orangutangs have this capability.

Doug · November 2006

An arm will end in a hand, which in turn may contain a spoon. Feet rarely do this. I think this lets bears in. Chimps and other primates obviously prequalify.
Pretty clear, I would have thought.

andy · November 2006

An arm: An appendage that may have the capacity to terminate in a spoon.

The problem with this definition is that loads of monkeys can pick stuff up with their feet.

David · November 2006

OMG. Someone intelligent has signed up to the forum, welcome Doug, I'd like to say i'd thought of that. But yes, monkeys can do stuff with their feet.

Doug · November 2006

I can pick (some) stuff up with my feet.
Which are attached to my legs!!
QED

David · November 2006

OMG. Someone who can pick stuff up with their feet has signed up to the forum.

andy · November 2006

QED - you've got four arms.

Doug · November 2006

That's nice of you to say so.

Pete · November 2006

Okay, my turn in this discussion, and frankly, ashamed that no-one thought about it. I'm reminded of that scene in A Scanner Darkley where they've lost there cognative processes.

What makes arms and legs?
Ultimately, the joints in them.
Arms are elbows and wrists. Legs are knees and ankles.

Notice how i didn't say shoulders and hips because of something like a horse, who's four legs are attached to hips and shoulders. This is more about muscles structure and the use of that part of the body. Evolution decided shoulders and collar bones are really good for hold necks and heads and hips are good for carrying guts and the like.

So, a horse has four legs because it has four knees and four feet. Apes and relatives have two arms and legs because of two knees and two elbows, but evolution throws another whatsit in the works (through environment) so they've develope MASSIVE upper body strength and longer arms to accomodate tree-swinging. Those short armed apes died out because they couldn't hold themselves for long.

As for the "hands" arguement, i call fowl. (See what i did there). Wings are considered evolutionary-developed arms designed for flight (hollow bones, long fingers, and feathers). I'll also like to mention frogs, no "hands" so they don't pick up stuff.

On another note: Dragons.
Wonderful myth that fails because there is no known spinal column arrangement that would allow for legs, arms AND wings. So they would be more like bats, with skin running from fingertip to hips. Apparently, this annoys animators of dragons, who have to build skeletons to animate the basic movements.

Same thing goes for angels.

Lucy · November 2006

that's the end of this thread then.

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What is an arm and what is a leg?

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