You may be thinking that a Major is senior to a Lieutenant so surely it should be Lieutenant General before Major General? Wrong...over the years Major General became a shortened version of the original Sergeant Major General. They obviously scrapped the Sergeant because it is a non-commissioned rank.
|Commissioned Officer ranks|
|Second Lieutenant → Lieutenant → Captain → Major → Lieutenant Colonel → Colonel →|
Brigadier → Major General → Lieutenant General → General → Field Marshal
|Junior & Non-Commissioned ranks|
|Private → Lance Corporal → Corporal →|
Sergeant → Staff Sergeant → Warrant Officer Class 2 → Warrant Officer Class 1