Anatomy: The Peripelvic Columns
In a simple cross section schematic of the rodent kidney, the inner medulla and papilla can be seen to be hanging within the pelvic space. When we remove this part of the renal medulla, we get a look at the pelvic tissue called the called the septum, which is continuous with the ureter. Each septum has a series of spokes which radiate towards the cortex and form the fornices. Between the spokes, the outer margin of the septum is free and has a semilunar edge.

The Hamster Kidney
Behind this edge the secondary pouches reach downward between the septum and the outer medulla. The bulges of outer medullary tissue seen in the urinary space are called peripelvic columns.

Bulges that are peri-pelvic columns

 
Other sections show that the peripelvic columns have flaps.

Peri-pelvic flaps
The fornices reach all the way to the cortex.

Deep Fornices
Capillaries are located directly under the thin epithelium, and it is likely that exchange of solute and water takes place between these capillaries and the urine reaching the pelvic extensions.

Shallow Capillaries