书城教材教辅科学读本(英文原版)(套装1-6册)
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第380章 第四册(36)

That part which swells up under your hand as the arm bends, is the great biceps muscle. It is connected at one end with the upper arm, and at the other with the fore- arm. When it contracts it becomes shorter and thicker. This is why you feel it swell up under your hand. Ofcourse, as it becomes shorter, it draws up the forearm. There are more than 500 distinct muscles in the body, and this is their common manner of working.

Lesson 11

The Oak and the Fir (a Comparison)

"In our last lesson on trees we took the oak as the representative of the dicotyledons or exogens," said Mr. Wilson. "There are a large family of timber trees-the firs and pines-which are usually classedwith the exogens, but they differ from

the oak and other timber trees in many important particulars. Let us find out these points of difference. Here are some acorns. These, you know, are the fruit of the oak tree. Take some of themin your hands and remove the seed from the outer shell. If you open it carefully you will see at once why it is called a di-cotyledon. It has the usual double seed-leaves.

"Now look at this pinecone. This,