阅读下面一首诗歌，完成小题。

帆

莱蒙托夫

                                                                                             那大海上淡蓝色的云雾里

                                                                                             有一片孤帆儿在闪耀着白光！……

                                                                                             它寻求什么、在遥远的异地？

                                                                                             它抛下什么、在可爱的故乡？……

                                                                                             波涛在汹涌——海风在呼啸，

                                                                                             桅杆在弓起了腰轧轧地作响……

                                                                                             唉！它不是在寻求什么幸福，

                                                                                             也不是逃避幸福而奔向他方！

                                                                                            下面是比蓝天还清澄的碧波，

                                                                                            上面是金黄色的灿烂的阳光……

                                                                                             而它，不安的，在祈求风暴，

                                                                                             仿佛是在风暴中才有着安详！

在哺乳动物的骨中，对骨的长粗和骨折修复起着重要作用的结构是（   ）