Ventral
View:
The membranes are back and now
we'll start our trip through the cranial nerves.
- The olfactory nerves (I)
are not visible. They bristled in a fine fuzz out of the bones
just ventral to the olfactory bulbs and when the brain was
exctracted from the skull they ripped.
- The stumps of the optic
nerves (II) are clearly visible as they course into the optic
chiasm. About half of the axons of each optic nerve
decussate (cross) at the chiasm. The optic tracts run
dorsally up the sides of the thalamus (not visible here)
heading for the lateral geniculate bodies (nuclei).
- The occulomotor nerves (III)
are distinctively flat and lie on the ventral surface of the cerebral
peduncles.
- The trochlear nerves (IV)
are like little strands of spaghetti that dangle down from the dorsal
surface of the midbrain.
Before moving on, note that in this
brain you can't see up into the third ventricle because the
soft tissue of the infindubulum has folded shut just caudal to
the optic chiasm. Also note that the mammillary bodies
in this brain create distinct buldges on either side of the
midline.