Around the bone chain, there were 3 layers of structure: skin, subcutaneous tissues and muscular layers.

尾椎链的外面覆以三层结构，即皮肤、皮下组织和肌层。

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Secondly project relevant background introduced the N-layer Architecturein software development, The software developer has put forward the concepts of 3-layers of structure in recent years.

其次项目的相关背景材料中介绍了软件开发的N-层体系结构，近年来软件开发商提出了3-层结构的概念。

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Secondly project relevant background introduced the N-layer Architecturein software development, The software developer has put forward the concepts of 3-layers of structure in recent years.

其次项目的相关背景材料中介绍了软件开发的N-层体系结构，近年来软件开发商提出了3-层结构的概念。

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