Hate to be an anatomy geek, but the humerus is the bone of the upper arm, not leg. The femur is the thigh bone.
The second bone from the left is a humerus, severed near the shoulder joint. It's upside down in the photo, the elbow at the top, but you can see the anatomy here:
http://en.wikipedia.org/wiki/File:Humerus_post.jpg
The third bone is a left tibia (shin bone) with a chunk taken out of it. It's upside down. You can see the malleolus of the ankle at the top right of the bore. That's the bump on the inside of your ankle. The blow would have been to the outside of the left lower leg, as one would expect for a guy fighting with a shield, his left foot forward.
Here's a picture:
http://en.wikipedia.org/wiki/File:Gray258.png
A femur has a big ball to fit in the socket of the pelvis to form a hip joint. None of these bones show that.
http://en.wikipedia.org/wiki/Femur
Bones aren't all that hard to cut through with a sharp heavy piece of steel. Butcher do it all the time. I have no trouble believing a blow to an unarmored limb could sever it.
But you generally don't have to cut through bone to incapacitate your enemy. The guy with the divot in his tibia probably had muscle and blood vessels severed by that blow, and likely was out of combat bleeding to death pretty quickly.
Sorry to be pedantic, but there are no severed thighs here.