My hair is already thinning on top.

我的头发已经稀疏了。

His hair is quite thin on top.

【thin，thinness】他头顶上的头发很稀疏。

His hair is quite thin on top now.

【quite】他现在头顶的头发很少了。

He was thin on top and thin-skinned about everything.

他是秃顶并且对任何事都很敏感。

But his legs look really thin on top and thick on the bottom, with kneecaps that stick out.

索尼娅：但他的腿看起来真的是上细下粗，膝盖骨突出。

Sonia continues, " But his legs look really thin on top and thick on the bottom, with kneecaps that stick out." Your legs connect your feet to the rest of your body, we could say.

索尼娅继续说， “但他的腿看起来真的很细， 下面很粗，膝盖骨伸出来。 ”我们可以说， 你的腿将你的脚连接到你身体的其他部分。