The pons forms the floor of the fourth ventricle like the open part of the medulla.

Much of the detail is within the H figure, outside it are the middle cerebellar peduncles.

How do you explain the appearance of the portion in the lower half of the 'H'?

What are two elevations in the floor of the fourth ventricle due to? You may guess the answer if you note the fibre bundles coursing down (ventrally) close to the midline.

What has happened to the tracts close the midline in the medulla oblongata?