Golgi study of the isocortex in an insectivore: the common European mole (Talpa europaea).

In the common European mole (Talpa europaea) the isocortex is a six-layered structure representing about 50% of the total cerebral cortex. The internal granular layer is narrow in the occipital region, however, probably reflecting a poorly developed visual system in an animal adapted to life in a subterranean environment. Golgi impregnation of projection cells and most local-circuit neurons of layers III-VI suggests a relatively well-developed isocortex in this insectivore. The presence of extraverted neurons in the so-called accentuated layer II and the amount of local-circuit neurons with very long beaded dendrites, however, probably represents primitive characteristics of the isocortex in mammals.