UNDER CONSTRUCTION -- COMING SOON
A good description of anatomical planes in a human can be found at https://en.wikipedia.org/wiki/Anatomical_plane. The transverse or transaxial plane is parallel to the floor (for a human standing on two legs), the coronal plane divides front and back, and the sagittal plane divides left and right.
For a mouse, imagine the mouse standing upright on its two hind legs looking upwards. The transverse or transaxial plane is parallel to the floor (divides head and tail ends of mouse), the coronal plane divides the front and back of the mouse, and the sagittal plane divides the left and right sides. Note that this convention is inconsistent with the conventional name of anatomic planes for the brain.