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托福听力考试背景知识综合辅导(三十三)

来源：网络发布时间：2011-02-17

    下面是托福听力背景知识，育路教育网特别为您搜集整理，内容如下：

    In human anatomy， the vermiform appendix （or just appendix） is a small sac connected to the large intestine. It was once believed to be a useless and purely vestigial organ； but newer evidence suggests it most likely has a function in the lymphatic system. It is one of a number of areas of the colon where lymphatic tissue is present； but in the appendix it is present in a particularly high proportion， although it degenerates with age and comes to resemble other areas of lymphatic tissue in the colon.

    The appendix is a small tube located at the end of the caecum， the first part of the large intestine. It is called vermiform appendix as it resembles a worm. It is usually eight to ten cm. long. Its structure is made of the same tough fibrous outer covering as protects the entire alimentary canal（消化道）。 There is a layer of muscular tissue under the outer covering and further a layer of lymphoid tissue（淋巴组织）。 The function of the appendix， which is performed by this lymphoid tissue， is to neutralise the irritating waste material generated in the body or the organic poisons introduced through the skin or membranes.

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