Zeitschrift für Anatomie und Entwicklungsgeschichte

, Volume 136, Issue 3, pp 272–293

The “extraverted neurons” of the mammalian cerebral cortex

  • Friedrich Sanides
  • Detlev Sanides


Ramon y Cajal (1909) adduced evidence that the pyramid cells of the mammalian neocortex have developed from the amphibian stage of the endbrain neurons with only subpial dendritic arborization.

The apical bouquet of the pyramid cells can be regarded as a conservative feature and the basal dendrites as a progressive feature in pallial neuron evolution.

In mammals only neurons of the primitive allocortices, the archicortex and the paleocorticoid, bordering the zonal layer, still represent approximately the amphibian level of pallial neuron evolution. They exhibit the extreme of dendritic extraversion in the mammalian cerebral cortex.

Intermediate forms with relative predominance of the external dendrites over basal dendrites are found in the layer II cell condensations of the periallocortex and proisocortex, i. e., the first and second growth rings of the neocortex (Sanides, 1970). This strongly contrasts with the well-balanced external (apical) and basal dendrites of the pyramid cells of layer II of the isocortex.

For all neurons with predominant subpial dendritic arborization the term “extraverted neurons” was proposed.

In a group of primitive mammals, hedgehogs, bat, and opossum, all over the isocortex moderately extraverted neurons of layer II were demonstrated, corresponding to the type which is found in other mammals only in the older growth rings of the neocortex. Also in these primitive mammals the extraverted isocortex neurons are bound to an accentuated layer II, which resembles the superficial cell condensations of the periallocortex and proisocortex.

Key words

Cerebral cortex Layer II neurons 


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Copyright information

© Springer-Verlag 1972

Authors and Affiliations

  • Friedrich Sanides
    • 1
  • Detlev Sanides
    • 1
  1. 1.Abteilung Neuroanatomie der Rhein.-Westf. Technischen HochschuleAachen(Germany)

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