View source for Paper - Structural organization of the human cerebral cortex prior to the appearance of the cortical plate (1983)

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| [[File:Mark_Hill.jpg|90px|left]] This 1983 historic paper by Marin-Padilla describes human cerebral cortex development. Only the abstract is shown online for educational purposes.

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'''Modern Notes:''' {{cortex}} | {{neural}} | {{CS18}} | {{CS20}}
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==Abstract==

The early development and the structural organization of the human cerebral {{cortex}}, prior to the appearance of the cortical plate (Carnegie stage {{CS22}}, ca. 54 days), was studied in two embryos: 43 (stage {{CS18}}) and 50 day old (stage {{CS20}}), respectively. 


It has been shown that the human cerebral cortex begins its ontogenetic development around the sixth rather than around the eighth week of gestation as it has been previously assumed. The human cerebral cortex starts to develop soon after the cerebral vesicles have been formed (stage {{CS15}}) and a primitive internal capsule has been established (stage {{CS17}}, ca. 41 days). 

By stage {{CS18}} of human development fibres from this primitive internal capsule have reached and probably have penetrated into the developing cerebral vesicle, through its more superficial zone. Fibres from this primitive internal capsule have been traced backward through the ventral thalamus to the mesencephalic tegmentum. The possible existence of primitive ascending fibres from the mid-brain which terminate in the superficial zone of the developing cerebral cortex (tegmento-thalamostriato-cortical tract) is suggested. The arrival of these primitive corticipetal fibres establishes in the outer zone of the cerebral cortex a primordial plexiform lamina or an external white matter. Horizontal-bipolar cells (embryonic Cajal-Retzius neurons) begin to differentiate by stage 18 of human development (43 days in our case). 

By stage {{CS20}} (50 days in our case), the primordial plexiform lamina is well established, extends throughout the entire surface of the developing cerebral cortex, and is considered to be functionally active. It is, by this age, a superficial, 40 micrometers thick, complex fibrillar neuronal organization composed of numerous horizontal corticipetal fibres (demonstrable with silver methods), horizontal-bipolar Cajal-Retzius neurons and a few other, less defined, cellular elements. This primordial plexiform lamina is considered to represent a primitive "premammalian" cortical organization. 

The next event in cortical ontogenesis is the appearance of the cortical plate or the mammalian neocortical grey at stage {{CS22}} (ca. 54 days). Migrating neuroblasts attracted toward the preexisting primordial plexiform lamina and guided by {{glia}}l fibres start to accumulate within it.