Fudgy
The simple answer is as Notso and Lancer say.
Additionally, the longit one is EITHER aligned with the body of the aeroplane in which case the set of axes are termed the Body Axes OR aligned with the airflow approaching the aeroplane when the set are called the Wind Axes. In the case of the wind axes you have to know angle of attack and angle of sideslip to position them.
All axes go through the CG – which answers Milt’s concern