skull

He had a fractured skull.他头骨摔裂了。

(informal) You need to get it into/through your thick skull [=you need to realize/understand] that you can't just sit there and expect everyone else to do your work for you!你这个笨脑袋怎么就不明白，你坐在那儿等着别人来替你干活是不可能的。

(informal) He can't seem to get it through his skull that I don't like him.他似乎怎么都不明白我为啥不喜欢他。