"yadehoo" "Duh, ok, no muscles in the fingers, that explains a lot why my fingers are still skinny after doing rock climbing, guitar and bass for so many years. So, they are in the forearm?"
Yes, according to Dorothy Taubman, Edna Golandsky, and every hand surgeon that has ever existed.
And, as far as "hardypractice" is concerned, the interossei muscles (located at the top of the hand) are used to twist the hand from side to side, and some think may aid in trill technique.
As any body builder can tell you, if there is not a parallel development of the ligaments and tendons associated with a particular muscle or set o0f muscles, then there will eventually be an injury. That is why anabolic steroids do not work - the muscles develop at a faster rate than the corresponding ligaments and tendons.
As a second year student, you are treading on very dangerous water by focusing on this for now. At the age of 64, I just got to where I can freely play any repertoire with my small hand with its thin and spindly fingers.
Give it time and patience, and it will get you there. Force it, and you may just ruin your hand.
And, you certainly will not be the first one to make this huge mistake.