At approximately day 1

CNS cellular proliferation and migration, most prominent in 2nd trimester (peaks during the 6th month), but continues to term.

Duration: 26 weeks

Reference

Evans OB, Hutchins JB. 1997. Development of the Nervous System. Chapter 5 In: Haines DE, ed. Fundamental Neuroscience. New York: Churchill Livingstone.

At approximately day 1

Interhemispheric, Sylvian, and transverse cerebral fissures of the cortex are recognizable.

Reference

Evans OB, Hutchins JB. 1997. Development of the Nervous System. Chapter 5 In: Haines DE, ed. Fundamental Neuroscience. New York: Churchill Livingstone.