生物
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第一篇（reptil）
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) p: N" ]: C# C2 w0 M/ \5 \M：Now I see professor Stone spent alot of the time talking about how animals walk and run. I remember she started by describing how humans move, and later we went over the gaits of different two-leg and four-leg animals. Like cats, camels, lizards...
3 G/ ]- I' t, q3 xW: Wait I think I missed class when you read over how lizards move. At least, I don't have any notes on it.
: N: R G! p+ k( aM:Well, we talked in class about how modern reptiles like lizards run. I think I even copy the diagram professor drew on the board. Here it is. Now , look at this. Lizards run with what's called as sprawling gait, their feet are well out on either side of their body and they move diagonally opposite feet together. The left fore foot with the right hind foot and the right fore foot with the left hinf foot. They use this way of moving when they're going slowly or quickly. When they move, they bend their bodies from side to side. And they time this bending so that they increase the length of their steps.
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kay. That' make sense. But I remember reading that, in general, animals evolves so that their feet are right under their bodies . But I don't see why?
$ o; ?( @7 Y8 M1 x1 r- g! D6 ?) y) }M: Well, that's because even the sprawling gaits suits lizards pretty well, there's a major disadvantage to this arrangement. Reptils can't run and breathe at the same time. They stop briefly between short breathes of anywhere from 2 to 12 strides because when they move from side to side, the muscle, of the left and right sides contract at different times. To breathe though, these muscles have to contract at the same time. Mammals don't have this problem because they don't move from side to side. Their feet are in the different position.
