To determine the development of the convolutional pattern of the cerebral hemispheres, we have examined multiple gross photographs of 507 brains and serial sections of 207 brains from infants of 10 to 44 weeks' gestational age. The sequential developmental changes of the individual fissures, sulci, and gyri of the cerebral hemispheres throughout the gestational period are tabulated. Schematic drawings made from enlarged photographs show the major changes associated with each month of the second and third trimesters.

The brains of twins between 19 and 32 weeks' gestational age show a delay of approximately two to three weeks in the development of convolutional markings compared with the brains of nontwins. There is no significant difference between male and female brains.

We found left-right asymmetries of the transverse temporal gyri, sylvian fissures, and planum temporale. In general, the right cerebral hemisphere shows gyral complexity earlier than the left. Our findings allow speculation about the significance of left-right asymmetry of the brain as it affects speech and language development.