Resolving the Confusion
The round can be very confusing. Hopefully this page will help straighten it out for you. In the simplest terms, the Round is the whole back leg of the beast. The photo shows a crosscut across the big end of the Round, Knuckle removed.
Compared to the Chuck (Shoulder) at the front of the beast, the muscles of the Round are much larger, much leaner and easier to work with than the smaller, more complex muscles and bones of the Chuck. They are also tougher, take longer to cook, and with so little marbeling fat they are less flavorful.
First Confusion: Top & Bottom: These designations have nothing to do with the cow. When a meat cutter slams the Round primal cut down on the cutting table to start cutting, the Top Round is up and the Bottom Round rests on the table.
In relation to the cow, the Bottom Round is on the Outside, away from the backbone. The Top Round is on the Inside, closer to the backbone. In other words, the photo shows a top view of the rear right leg of a cow that is facing to your right and tail to your left. Only meat aft of the leg bones is shown. That on the forward side (Knuckle) is much shorter and handled quite separately.
The Ends: The Top, Bottom and Eye rounds all run from the Sirloin End (the big end) to the Shank End (the small end). These muscles are at their tenderest (not really tender, though) at the Sirloin End, and become progressively tougher with more connective tissue (and more flavor) toward the Shank End.
The Leg Bone: It would be in the notch at the right in the photo. All the meat shown is toward the rear end of the beast, behind the leg bones. The Knuckle cut (Sirloin Tip) is forward of the leg bone and is not shown in this photo.
Top Round: This is the big muscle at the top of the slice in the photo. It is on the side of the leg closest to the backbone and is generally more tender than the Bottom Round.
Bottom Round: This is composed of the wedge shaped muscle in the lower center and the block shaped muscle at the bottom right. It is on the outside of the leg, away from the backbone, and is generally tougher than the Top Round.
Eye of Round: This is the oval shaped muscle at the lower left in the photo. It is on the outside, away from the backbone and at the rear of the beast, but is more tender than the Bottom Round.
Knuckle / Sirloin Tip: This muscle structure is on the forward side of the leg bones and is not shown in the photo as it is handled very separately from the meat aft of the leg bones.
Rump Roast: This cut is from the Sirloin end of the Bottom Round - in other words, it's up at the rump.
More on Cuts of Beef.