Breakdown of Liðurinn í þumlinum á mér er bólginn.
vera
to be
ég
I
í
in / into / to (before the hour, in telling time) / per (in frequency expressions)
á
onto / on / in (static location) / on (a day of the week)
Questions & Answers about Liðurinn í þumlinum á mér er bólginn.
Why do we say þumlinum á mér instead of þumallinn minn?
This sentence uses the standard structure for external body parts: the definite noun (þumlinum) plus á and a dative pronoun (mér). Instead of saying 'my thumb', Icelanders say 'the thumb on me'.
Why does þumall (thumb) change to þumlinum in this sentence? Where did the second 'a' go?
Words ending in -all often drop their second vowel when an ending is added. Because the preposition í (in) requires the dative case for a static location here, þumall becomes þumli. Adding the dative definite article -num gives us þumlinum.
Why doesn't the adjective bólginn (swollen) match the dative case of the thumb?
The word bólginn describes liðurinn (the joint), which is the main subject of the sentence, not the thumb. Since liðurinn is a masculine, nominative noun, bólginn must take the masculine, nominative form.
Since the joint is inside the thumb, why do we use á mér instead of í mér?