Cell counts for the stratum pyramidale of the hippocampus of the rat

The number of neurones in the stratum pyramidale of the hippocampus of the rat has been estimated as 260,000. The neuronal populations for the various sub-fields of the hippocampus on sections transverse to the long axis of the structure have been found to be in approximately constant ratio to each other - $\text{CA}\text{1:}\text{CA}\text{2}\text{3}\text{:}\text{CA}\text{4 = 2:4:1}$. The constancy of these ratios provides quantitative evidence in support of a regular organisation of the hippocampus in lamellae transverse to its long axis.