'How comes it' or 'How come is it'?

I was reading this paper and I came across this sentence, which I found quite odd.

In the words of Bertrand Russell, the problem is this: “How comes it that human beings, whose contacts with the world are brief and personal and limited, are able to know as much as they do know?”

Shouldn't it be 'How come is it' ? It just doesn't sound right, maybe because I am not a native speaker.

No. How come is it doesn't make sense.

How comes it is an example of an older syntax of English, which you can find readily in sources such as Shakespeare and the King James Bible. In modern speech this has been entirely replaced by How does it come, but we still use the older syntax with auxiliaries: how is it, how can you etc.

I think that in Russell's day, though this form was in general obsolete, how comes it had survived as a literary idiom.