It's a 23.4SC ref CK 650. Although it is presented as such in AJTT p.126, it isn't what Omega named 'Medicus' in the 30's, this name was only for the first 23.4SC model ref CK651, with square case.
It is however an interesting an unusual model. Serial numbers date it from around 1939. Dial and hands seem original, even if it is difficult to juge on those pictures. The part that keeps the central second hand pinion in place (don't know the name in English) is not original.
Mine (same dial, different but also original hour & minute hands, probably wrong second hand, right crown) says hello :
Click to expand...