The AC is a compact bundle of about 3 million myelinated nerve fibers connecting aspects of the left and right temporal lobes (including olfactory cortex and the amygdala) across the midline. The AC is a useful marker in CT scans, it crosses the anterior 3rd ventricle just behind the lamina terminalis and about 8 mm above the optic chiasm. In addition to cortical crossing fibers, the AC also has axons from the anterior olfactory nucleus en route to the contralateral olfactory bulb. It is not to be confused with the anterior (white) commissure of the spinal cord. It is much larger than the “posterior commissure” of the pretectal area of the midbrain, but far smaller than the corpus callosum.
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