Brain – Optic Chiasma

On the ventral side of the sheep’s brain, several nerves and structures are visible after the careful removal of the dura mater.   The image below shows the brain with the dura intact and the eye socket attached.  The blue reflective surface of the sheep tapetum can be seen, though the other parts of the eye have been removed.

brain and eye

When the dura is removed and the eye has been cut at the optic nerve, it is possible to see where the two optic nerves cross at the optic chiasma.  Images from the left eye are conveyed to the right side of the brain and vice versa.    Also visible in the photo are the two olfactory bulbs attached to the olfactory nerves, much larger in sheep than in humans and account for the sheep’s keen sense of smell.

The pituitary gland is usually removed with the dura, but the pituitary stalk (infundibulum) can be seen just anterior to the mammillary body of the midbrain.   Mammillary bodies are thought to be related to spatial memory.  optic chiasma