The number and the distribution of the apical dendritic spines was investigated in the layer V pyramidal cells of the human cerebral cortex. This study was carried out in the motor cortices of an 8‐month fetus, a premature infant, and a newborn, 15‐, 19‐ and 45‐day‐old infants; in the somesthetic cortex of a newborn infant; and in the auditory cortex of a newborn infant. This study has shown: (a) that the number of spines increases with the age, (b) that the spines are distributed along the apical dendrites in a characteristic manner which, graphically represented, consists of a curve with three distinct deflexions, (c) that the spine‐distribution along the apical dendrites of the layer V pyramidal cells is similar in all cases studied regardless of their age or their cortical location (motor, somesthetic and auditory cortices), (d) that the distribution of the spines along the apical dendrites appears to depend on the nature of the dendrite, (e) that the sequence of the mean number of spines maintains an exponential relationship with the distance from the cell body for the first and second deflexions of the spine‐distribution curves. The significance of the distribution of the spines along the apical dendrites of the layer V pyramidal cells is discussed. A new method is presented and its possible application to the study of the normal development and pathoIogical conditions of the cerebra1 cortex is suggested.
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Miguel Marín‐Padilla (1967) studied this question.