This is an axial view of the shoulder.
2 is anterior to 3, ie the upper part of the film as displayed is anterior.
It demonstrates the os acromiale, an unfused acromial apophysis. The acromial apophysis is a secondary ossification centre which normally fuses aged 18 to 20 years. This appearance is a normal variant which is often mistaken for a fracture on the axial view. It is usually bilateral.