However, animal models may be insufficient to elucidate the complexity of these systems. Pyramidal cells in CA1, for example, are 30 times as thick in humans as they are in rats. The entorhinal cortex is also subdivided into as few as 8 and as many as 27 sections in humans (depending on the system used), whereas there are only 2 in rats and 7 in monkeys. The connections of the dentate gyrus and entorhinal cortex are also more sophisticated in humans. In rats and cats, a very large reciprocal connection exists between the entorhinal cortex and the olfactory system. In primates this connection is absent and there are highly differentiated connections between the multimodal parasensory and paralimbic cortices and the EC which are not as evident in rats and cats. The increased size of the primate subiculum may proportionally enhance its effects on the entorhinal cortex.