In the avian cerebrum and in the spinal cord, sympathetic ganglia, hypothalamico pre-optic area and cerebral cortex of the rat sexually dimorphic' nuclei are clearly recognisable. Similar differences have been described in the human brain. Morphometric analysis has shown a sexually dimorphic nucleus in the pre-optic area. There is continuing controversy over differences in the size and shape of the corpus callosum, but there is accumulating evidence of cerebral asymmetry with more focal representation of language and praxic functions in the left cerebral hemisphere in females. The various sensory modalitites also show gender differences. The significance of these secondary sexual variations in brain structure resides in the developmental and behavioural characteristics of the underlying neural circuits.
