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This study aimed to clarify the development of sulci and gyri on the external surface of the cerebrum of cynomolgus monkeys. Sulcus formation began with the appearance of the lateral fissure on embryonic day (ED) 70, followed by delineations of four cerebral lobes by the emergence of the parietooccipital sulcus, central sulcus, and preoccipital notch on EDs 80-90. The following primary sulci were then visible until ED 120: the superior temporal sulcus on ED 90; the intraparietal sulcus, lunate sulcus, inferior occipital sulcus, and arcuate sulcus on ED 100; and the principle sulcus on ED 110; the occipitotemporal sulcus, anterior middle temporal sulcus, and superior postcentral dimple on ED 120. These sulci demarcated the superior temporal gyrus on ED 90, the precentral gyrus, supramarginal gyrus, and angular gyrus on ED 100, and the inferior and middle temporal gyri, postocentral gyrus, superior parietal lobule, superior, middle and inferior frontal gyri, and inferior occipital gyrus on ED 120. Except for the intermediate and lateral orbitofrontal sulci, the sulci that appeared on ED 130 and thereafter were not related to the gyrus demarcations. Intriguingly, the brain markedly gained weight on EDs 100 and 120, corresponding to the embryonic ages when almost all gyri were visible. The results suggest that a rapid growth of the cerebrum involves convolutions of the gyri by a regular sequence of the sulcus formation in cynomolgus monkeys. This study further provides a standard of reference for normal development in the cerebral cortical morphology of cynomolgus monkeys.

The present study aimed to clarify sulcation and gyration patterns in the developing cerebrum of ferrets. While the brain weight and fronto-occipital length of the cerebral hemisphere reached a plateau by postnatal day (PD) 42, the cerebral width reached a plateau at the rostral region by PD 21, and subsequently at the caudal region by PD 42. The ferret cerebrum already showed a convoluted surface with indentations of coronal and rostral suprasylvian sulci on PD 4. The presylvian and cruciate sulci emerged by PD 10, resulting in convolutions of gyri in the rostral half of the cerebrum. The caudal half of the cerebrum was infolded by the emergence of the pseudosylvian sulcus and the rhinal fissure by PD 10, and the caudal suprasylvian and lateral sulci by PD 21. The emergence of those sulci allowed a gyration in the caudal half of the cerebrum. Sexual differences in sulcation were detected by a more distinct convolution of the visual cortex in males than in females on PD 90. Those results, therefore, suggest that the ferret cerebrum experiences cortical maturation with sulcation and gyration in a rostrocaudal gradient manner. The present paper provides neuroanatomic references for normal development of cerebral sulci and gyri in both sexes of ferrets.

Our article summarizes a series of studies about fetal gyrification and its relation to cerebral growth in cynomolgus monkeys. Based on the cerebral growth (i.e., brain weight, cerebral volume, and frontooccipital length of the cerebral hemisphere) and the developmental pattern of gyrification in each sulcus of cynomolgus monkeys, we divided the gyrification process into four stages: Stage 1. Demarcation of cerebral lobes and limbic gyri; Stage 2. Demarcation of neocortical gyri; Stage 3. Emergence of secondary and tertiary sulci; and Stage 4. Growth of sulcal length and depth. Each stage of those gyrification processes was influenced by different developmental events, such as the emergence of corticocortical long-associative fiber tracts, cortical maturations, and subcortical white-matter development. This is the first report to systematically propose gyrification processes closely related to the order of phyologenetical development of the cerebral cortex in primates.