The Dennis Rectangular maze is a 3 x 4.5 feet (the inside measurements were 36″ x 54″ x 7″) with two removable cross-walls running the width of the maze. The first cross-wall was placed 9″ from the start, and the second cross wall 18″, from the wall through which the rats entered the maze. The opening in the first cross-wall was 5″ high and 8.5″ wide, occurring 18.5″ and 19.5″ from the left and right sides respectively.

The second crosswall was 27.5″ long, leaving an opening of 8.5″ next to the left side