The meaning of "so lain"

English as a Second Language English Vocabulary, Grammar and Idioms
1

Hi teachers,

Please look at this extract.

[color=blue]…; in other word, that the entire family lay in the direct line of descent, and had always, with very trifling and very temporary variation, so lain.

What does “so lain” mean?

Thanks beforehand

Jupiter

2

Hi Jupiter,

In your sentence ‘so lain’ means had always lain (been in that position of lying in a direct line) in this way.

Alan