There is no evidence that neural connections or brain architecture are any different in men than in women, although at all ages the average brain mass of men is approximately 10% greater than in women. That difference can probably be attributed to the difference in neuron size rather than number, and it does not imply differences in performance (Spreen, Tupper, Risser, Tuokko, & Edgell, 1984). Differences in mass between the two hemispheres (right hemisphere has greater mass, whereas the left has greater density) are smaller in women than in men. Thicker cortex of the right hemisphere as compared to the left has been found in male, but not in female, fetuses. The shape of the left lateral (Sylvian) ssure corresponds to the right in more women than men. In women, the left planum temporale is not as frequently larger than the right as it has been found in men. Relative brain size is different at 2 years of age, and in the hypothalamus, sex differences occur around the fourth year of life (Swaab & Hofman, 1995).