8 of 44Image
The top of the main case is held in place by tabs. These tabs (red arrows) are released with a gentle twist of a flat-head screwdriver.
The layout is very utilitarian - making judicious use of expansion slots.
It is also very dusty - our poor PC Jr. has obviously been neglected. But it still works - they don't make'em like they used to I suppose.
The 5 1/4 floppy drive in the IBM PC Jr. is remarkable for its size -- it is huge and takes up one whole side of the case.