THE POSTNATAL ONTOGENESIS OF THE VISUAL CORTEX OF THE RABBIT

The postnatal morphological development of the visual cortex was studied on the basis of Nissl and Cox preparations. Sixty seven rabbits, with ages ranging from newborn to adult, were used in the present investigations. The following results were noted: The development of the visual cortex in the rabbit was divided into two stages, namely, the rapid developing stage (the period from birth to the 15-20th day) and the slow developing stage (the period from the 15-20th day after birth to adult). During the first stage there was a rapid increase in thickness of the cerebral wall and rapid reduction in cell density of the gray matter, due to the growth of individual neurons, especially, in the upper layers (layers II-IV). The cytoarchitectonic lamination of the cortex became distinct too. During the second stage there was little further increase in volume of the gray matter. The development of the white matter appeared to gain speed, however. No definite relationship between the thickness of the cortex and the weight of the animal was found. At about the 15th day after birth the cytoarehitectonic lamination of the visual cortex already attained its mature pattern, and the cortical neurons also showed characteristics of maturity. It is therefore concluded that the visual cortex of the rabbit matures morphologically at the 15-20th day after birth.